Porsche 928 Electrical FAQ
Porsche 928 Alarm
Question
Hi Folks,
I have a fairly major delimia at the moment. Our ’81 auto apparently has the factory “anti-theft” option, as it has decided to activate itself. As described in the owners manual, when we open a door, the alarm (beeping horn) sounds for 30 seconds, and of course the car won’t start. The problem is, we do not now, nor have we ever had, the “long S key” required to activate and deactivate the system. Can someone please tell me how to deactivate the system without the “S key”? It is possible to easily deactivate the system altogether in order to eliminate this happening again?
Thank you one and all for your consideration of this matter.
– David Moody Jr.
’78 5sp
’81 AT “secure in the driveway”
928OC & PCA
Response(s)
David,
The alarm is activated by momentarily ground of the activation lead on the back of the door locks. It is possible that one of these leads got grounded and activated the alarm. This would suggest that there is some kind of short in system. The alarm horn is under the right front fender and is accessible by removing the blower fan, which is no small job. The control unit for the alarm system in located under the dash up high. I think the only way to get at it is to remove the dash Porsche buried these components for the obvious security reasons.
The alarm unit is integrated into the ignition switch and the dome light switch in the doors (which I would clean just for drill). For some reason that I have yet to figure out, Porsche put preference on the passenger side door switch to reset the system. Go figure. You can have a long key made from the VIN number – 928 International provides this service. There are also local key shops that will make a long key from your passenger lock and the short key – I have the name of one in the SF area that is set up for this. Now I have told you all the proper ways to fix the problem here is a couple of work arounds. The blue, green and brown wires going to the door control the alarm. These can be accessed by removing the door panel and are attached to the lock with a plug along the top of the door. They can also be accessed in the kick panel by the door as the wires go through the plastic shield to the door. This is the best place to look for a short as well. If you contact one of these wires – I can not remember if it is the green one or the blue with the brown wire momentarily the alarm will turn off and everything gets reset. To hack things you might want to rig up a momentary contact switch to act as a dead man’s switch and thus have a way to disconnect the alarm system the next time you get stuck. If you combined the hidden two way center off monetary contact switch along with clipping the wire to the alarm horn you would have in effect a safety silent alarm that you could activate when you needed it without the use of the long key.
Hope this helps
Dan
928
Question 2
Dan,
Can’t you also disable the alarm by disconnecting the blue/green/brown wires in the door? There is a connector about midway back on the top of the door (after removign the panel) where you can disconnect them.
Mike
86 5spd
Response(s)
Mike,
That is exactly right and I did mention this connector. But you do have to remove the door panels and there is a possibility that the activation of the alarm is coming from a different source. Disconnecting the alarm and not having a way to turn it off again should it ground out once again is a bit short sighted – especially if you are planning on trusting the car to get you someplace reliably. The question becomes – without the long key how did the alarm get turned on in the first place??
My conclusion is that there is a short in the alarm system somewhere. It could be in the doors or any other place. The next suggestion I would make is buying a signal tester (Fox and The Hound is the one I use) and trace down the source of the real problem.
Dan
In a follow-up message dated: 9/7/00
To everyone who responded to my alarm self activation problem – Thank You!
1. I now have more alarm wiring info than in contained in the manuals, which can only help in the future.
2. Based on comments made and a look at the manuals, and realizing that the last alarm system related area we were in was the rear, as we had the tools and everything else in the rear of the car out for last weekend’s “open track AX” at Gingerman, I found a badly corroded plug at the rear hatch latch. I unplugged it – Car now runs!! Which is good, as we have a three day PCA DE starting tomorrow mourning.
3. I am going to go ahead and order the long “S key” any way, in case the door contacts ever act up.
Thanks again and have a great day.
– David Moody Jr.
’78 5sp
’81 AT “secure in the driveway”
928OC & PCA
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SECTION 2: Windows
In a question dated: 10/25/00
My passenger side window is stuck in the down position. If I press the down switch, I can see it drawing current, however it doesn’t seem to draw anything when I try up. Similarly, the drivers side draws power both ways. So I’m thinking I must have a bad switch.
All I want to do is get the window UP for now. (No garage. You can imagine the ramifications of leaving a window down, especially this time of year in Missouri.) There are four wires going to the switch: red, black, green, and brown. Is there a way of shorting them in order to get the window motor to push the damn window back up?
Julian Cates
86.5 928S
Response(s)
Julian,
It is possible that your window switch “points” are just carbonized (the same goes for seat switches too). The older 928 model window switch top can be gently pried open to exposing the switch frame – points. I’m not sure of the MY for the change in switch design. Be very careful, you’ll destroy the new type switches when trying to remove those caps, no cleaning for these.
There are actually two sets of copper frames in the switch, one for up and the other for down. They are in opposite orientations. Be sure to note the orentation before removing them. Use a fingernail file to lightly remove the carbon on the copper arm side and just use a screw driver for the opposite side.
Rich
’93 GTS [new style switch]
’83S [old style switch]
Response(s)
The big change in switches was 1990 model to a low amperage switch that talks to a control unit . The older style has two iterations the original very early unit with coil springs and ball bearings or the replacement superceded version with the flat contact plates . If you pry open the coil spring / ball bearing contact style you will immediately know that it had springs and balls . What you will not know is where they are now !!!!
Jim Bailey
Response(s)
Rich,
I would be real careful when doing this procedure. First disconnect the battery or the switch. If a ball bearing from the switch falls down in to the switch it can short out and cause the plastic to melt. The second bit of caution is to be in a place where you can collect all of the parts without dropping them down behind the seats or having springs bounce off the headliner and go who knows where.
For cleaning I would recommend something with finer grit than a finger nail file – like maybe 600 Wet or Dry.
When putting the switch back together I have found that a bit of super clue helps to hold things in place during assembly. I will be damned if I know how the factory got these assembled. Sore like the final ad in “Crazy People”.
Dan
SECTION 3: Dash
Question
Hello all! I was driving today and my ampmeter needle droped to nine and the red light came on. Car ran fine, but the needle would not move above 10. When I would use an electrical system such as lights or brake lights, the needle would drop to nine, but never return to anything above 10. Should I continue driving the car with this light on? Does this sound like a problem with the voltmeter or the alternator? Diagnosis anyone? Thanks for your help in advance.
David Lustick
’82 928 auto
In a response dated: 9/21/00
I had a similar problem when a diode broke off inside my original alternator. I think your ’82 uses the same Paris-Rhone alternator that was also OE on my ’83. The design of that alternator leaves a lot to be desired and it wouldn’t have a prayer of passing for mil-spec. The diodes look like the wheels on a Hot Wheels car and are precariously soldered on top of what looks like a rejected Bic pen spring. I ended up replacing my alternator with a rebuilt Bosch unit that has been great for the past 5yrs. I’d be inclined not to drive the car until the problem is fixed.
Jim Stadter
’83 928 S 5-speed (U.S. spec)
’88 928 S4 5-speed
Lone Star Region PCA (Austin) 928 Owners Club (http://www.928oc.org)
In a response dated: 9/21/00
first i would check all the simple stuff. like battery cable connections tension of the alternator belt, blown fusesets. then if you still don’t find anything, take it to a reputable electrical shop and they can diagnos a bad alternator or voltage regulator etc….. just a place to start, wish i could be more help… Bobby ’91 GT
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Faulty Console Lights
In a question dated: 3/4/99
Body:
I’m not sure (just got car Tuesday), but at night the lights on the console for the windows, sunroof,rear wiper, do not light up. Is this a bulb problem or a fuse problem? And if a bulb problem, how do I replace it? I don’t want to tear it apart until I know what to do.
TIA
Christine
“Save the Flash”
In a response dated: 3/4/99
Hello Christine,
Welcome to the 928 world. I think I recall that you purchased an ’84 model (please include this info, it helps troubleshooting).
First, there are three switch settings on each light, on controlled by door switches, manually “always on” or manually “always off.” Check this first, you want the controlled by door switch setting. [The door lights have rocker switches, the whole lens rotates for the windshield/roof/luggage compartment]
If tinkering with the switch settings don’t produce light, the next step is to check the fuse. The fuse box is under the passenger compartment VERTICAL-most footrest (unhook the carpeting straps and peel it back, there is a wooden panel that either swings up (hinged at the top) or pulls completely out. A great fuse chart can be found on Dave Roberts’ website: www.928gt.com click on tips, 928 specs and technical info section, fuse chart. For an ’84 the revelent fuse number is #23 (upper left being #1), it supports Inside Lights, Clock, & Tailgate Release, and is an 8 Amp fuse.
If the fuse is good, next check the door/hatch switches.
I hope you’ll see the light!
Rich
’93 GTS
’83S
CM 928 OC
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Stop Warning Lamp Doesn’t Go Out
In a response dated: 8/1/99
I had the following happen on my 89 S-4 5 speed yesterday. I started my car about mid day and noticed that the stop lamp warning light didn’t go out after I tapped the break pedal for the first time. Along with the lamp remaining on, the headlights wouldn’t raise, the sun roof and windows were inoperable, the windshield wipers were dead, neither speedometer worked, the odometer didn’t work and the fuel calculations on the digital display didn’t compute. I shut the car off after driving several miles and fired it right back up. Everything has been working fine from that point on. If anyone has any thoughts they would be appreciated.
Thanks,
Mark R.
In a response dated: 8/1/99
Mark:
This sounds a lot like the ignition switch. The ignition switch can be diagnosed if/when the problem happens again. Try jiggling the key in the lock/switch and see if the “X”-functions return. The switch is a little bit of fun to replace, so you may find that “adjusting” the key in the ignition lock will suffice as a cure.
The “X” bus is tasked with providing power to all the car’s functions that normally associate with the “accessory” key position. The “X” bus is energized directly through the “accessory” contact on the ignition switch. Once the “X” bus is energized, each of the accessories you mention is switched through individual subsequent relays and switches. The ignition switch is the only point where a single failure will cause the multiple symptoms you describe, absent a failed wire.
dr bob
’89 S4 AT
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Speedometer, Odometer Repair
In a question dated: 11/12/00
Okay, I’ve been to Greg Nichols excellent site and have managed to get the instrument cluster out of the car…no problems. Now, I am trying to get in to find the source of my malfunctioning odometer (it’s probably those notorious plastic gears). However, I can get totally in. The screws on the back of the speedometer portion of the cluster won’t get me to where I need, so I have to (I think) go in from the front. Question: How do I get the speedometer needle off so that I can remove the faceplate and get all the way to the odometer gears and motor? It seems to be on really tight, and I’m afraid of breaking the thing. Could someone please tell me if I’m on the right track here?
Guy DuHamel
81 5spd
In a response dated: 11/12/00
Guy,
The Speedo needle is a light press fit on a sewing needle sized hardened steel shaft. If just pulls straight off. Then the face plate comes off with I think two microscopic screws (slotted head style). Then you can get the front bits off to isolate the cause. There is one gear that is notorious. If there is one that looks like yellowed old smokers teeth (sorry if that offends anyone I couldn’t come up with a better description) it shouldn’t be and that’s the problem. When that gear is new it is translucent white and a bit rubbery. Look at the smaller inner teeth of the double gear and you should see about 2/3 to 3/4 of the width chewed away. That’s why sometimes the car will clock miles after hitting a bump in a hard turn. Normally the plastic holders are a bit loose and the gear spits out of alignment and the teeth are ground off. A proper repair will also look at alignment as well as replacing the old gear.
Jay Kempf
In a follow up message dated: 11/12/00
Thanks guys! I’m in. The speedometer needle simply popped off after I threw the unit against the wall in frustration……just kidding. The problem does seem to be the first gear after the worm drive just as Jay Kempf described. Everything else looks to be in order except for that gear missing three teeth. Now for question number two: Does Porsche or anyone actually sell these gears? I guess I could spend the winter trying to whittle one out of a block of hickory or something, but this doesn’t really have much appeal. The only part number I can find is one the whole odometer/trip meter assembly, and I can just imagine what Porsche will charge for that. Anyone have any suggestions?
Guy DuHamel
Kitchen table covered in little gears (wife unamused)
81 5 spd
Voltmeter
In a post dated: 3/29/2000
Jason D Wheeler wrote:
Is this the beginning of the end for my alternator? Or is it something much simpler (read: less expensive)?
A couple of days ago, the voltmeter guage on the dashboard starting going haywire. It would be fine for a while giving off a reading of just under 14 most of the time, but then suddenly would jump through the red zone to the top of the guage (16) and beyond(!?) for a matter of seconds before settling back to it’s normal reading. I thought at first that perhaps the guage itself went on the fritz (as they are known to do); however, these increased readings were actually accurate judging from the intense brightening of the headlights and the higher pitch whine of the fuel pump and/or cooling fan (if any of them happened to be audible at the time). So my guess is that something in the electrical system is no longer doing its job of ensuring that only the right amount of charge flows to the various systems and back to the battery. Forgive me if my knowledge of electricals (like most things mechanical) is elementary at best.
Could this be a problem caused by the impending failure of my alternator, or is there a regulator in the system somewhere that is no longer monitoring the charge shooting through the components?
It’s nice having supercharged components, but I’m afraid at this voltage, many components are doomed for failure, or even worse, could I be sitting on a timebomb (potential battery explosion)? Fortunately, the surge in electricity only last a few seconds at a time, but I noticed it getting longer in duration
Good job of observation and reporting, and a good guess on the problem.
In a response dated: 3/29/2000
The alternator sounds fine. Yes, there is a voltage regulator mounted on the alternator. Either that regulator is failing, or it is not accurately measuring battery voltage due to a wiring problem. The regulator/alternator uses the battery as a reference voltage and voltage stabilizer, and having the battery come disconnected while the alternator is charging the system can cause serious voltage spikes that can damage almost any of the electrical components on the vehicle. Murphy’s Law assures that the damage components will be either the most expensive (such as a computer) or most difficult to replace (such as a major wire harness).
A brief spike won’t hurt the battery, and long term slight over-charging is more likely to damage the battery than brief high voltage.
The suggestions that you have received thus far about accurately checking the system voltage are right on the money, but I’m afraid that the bright light and fast fans tell the tale. The voltage regulator is the easiest answer, but if a new regulator doesn’t solve the problem, you may be in for a frustrating gremlin hunt.
As a simple first step that may or may not solve the problem, but should be done periodically anyway, open the battery box, remove the ground strap (which on your ’84 should be held by the infamous wingnut!), then remove and carefully clean the battery posts and terminals and the chassis ground cable and connection point.. Disconnect the chassis ground first, then the battery ground cable, then the positive cable. Replace in the opposite sequence, ending with the chassis ground. If you are luckier than you can expect, that will solve the problem, but don’t count on it.
You can buy an alternator from us or any of the other suppliers, or you can have the alternator rebuilt, including a new regulator, brushes and bearings, locally at any good automotive electrical shop. Be sure that the alternator cooling cowl and hose get reinstalled.
Wally Plumley
928 Specialists
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Section 4: Seats & Doors
In a question dated: 7/3/00
hello Renners…I have a seat problem…It gets stuck moving forward & back sometimes …I can hear the motor clicking like it’s trying to move..but no go…
doesn’t look like anything is obstructing it like carpet..etc…I’ve heard of the tedious taking the switch apart fix…I think my mechanic will have that pleasure…
Is there any advice out there?
In a response dated: 7/3/00
You may be hearing the relay under the seat clicking, rather than the motor.
If you hear a clicking, the switch is probably OK.
Since you hear a clicking, the switch and relay are probably OK. It sounds like either a problem with the motor or its wiring, or a mechanical binding. First thing to do is to try to find why the seat isn’t moving.
If you can see under the seat with the aid of a mirror, you might be able to tell whether the cables are trying to move or not. You can also try the emergency manual drive on the front of the seat, and see if there seems to be any binding. You may need to remove the seat so you can check it out.
One bolt in front, two in the rear on each side.
Wally Plumley
928 Specialists
Locking and Unlocking Doors
In a question dated: 10/30/00
Hello,
It probably doesn’t sound strange. Took a while to believe it until I actually saw it with my own eyes. You know, you leave and lock the car, come back and it’s unlocked. Alarm is still active. I’ve lockedthe door, stood there and watched it somewhat quickly unlock on its own after 15 seconds or so. No, no keyless entry system. This seems to occur more often in hot weather. Happens pretty consistently. Live in SW Florida where it gets pretty hot and humid.
Jason 87 S4 AT RMB’d
In a response dated: 10/30/00
Hi Jason, i live in the Northeast part of Florida and the same thing happened to me last month, the problem was a low battery, 2 days on a trickle charger and driving the car more often fixed the problem, i know it is strange you think your crazy!, like i did lock the car and then locks pop back open on you, good luck!, Mark
In a response dated: 10/30/00
Hi Jason!
Can’t tell you for sure what is going on, but I had the same problemon my ’82 and eventually traced it to flaky contacts in the passenger door lock motor. A replacement cured the problem.I also had the symptom, of the passenger door lock cycling from time to time when the SO tried to exit the car… She swore the car hated her until I fixed it. 🙂
-Larry Ware
82 auto Moosgrunmetallic (Moss Green Metallic)
928OC charter member
Florida plate: “V8 SHARK”
lrware@pipeline.com
In a response dated: 10/30/00
I had a similar problem. Turned out to be the microswitch in the keylock which controls the central locking that was faulty. Had to exchange it.
Johnny Billquist
In a response dated: 10/30/00
Porsche likes to use motors as switches – door locks , headlight motor , rear hatch motor ,windshield wiper motor. The door lock motor is moved when you manually lock the door . The motor of the door you locked tells the other door motor “Ok I am Locked now you also should lock” so the second moves electrically but if it does not move far enough it tells the first lock . “Hey I am not locked so you should open ” when it is really not working correctly they will cycle open ,close, open, close . Using the round knob on the inside of the door may change how the motors respond as it moves the motor .
-Jim Bailey
Seat & Mirror Connectors
In a question dated: 5/23/99
Took off both door panels yesterday. Needed to glue the top vinyl that lifted. I noticed the passenger side had the same connector as the drivers side for the seat and mirror memory buttons. Does anyone know why this connector is inside the passenger side without being connected to anything? Is their a memory setting for the passenger seat on a newer model? What is the typical oil consumption of the 928? Leakers excluded 😉
John Veninger
1990 928GT
928OC
In a response dated: 5/23/99
That is indeed the wiring connector for the passenger memory seat option, since all 89 and up have the drivers seat memory standard (excluding Sport Seats) , they are pre-wired for the passenger option to save Porsche the hassle of making 2 different wiring harnesses. All you need is a memory passenger seat and the door panel switch to upgrade your passenger seat to have the memory function, sort of like a “plug n play” thing 😉
David Roberts
928 SPECIALISTS
SECTION 5: Headlights & Seats
In a message dated: 7/27/99
Just a thought for those thinking about high-powered bulbs–
On my ’89 US car with H-5 (9004) lamps, the sockets died a slow agonizing death around the ground terminal at the bulb. This is with 80/100 bulbs and otherwise stock wiring. The sockets have been replaced with better (so far…) aftermarket parts, and everything seems fine. On my list this weekend is the 100w fog and driving bulb upgrade, along with replacing that cracked lens. Fortunately, the H-3 fog/driving bulbs don’t have sockets, so all they need is a little Kynar wiring inside the housing to keep them happy.
The H-4 type bulbs used in the non-USA lamps used to be available in ceramic, and are currently available in higher temp plastics. May be worth investigating as part of the whole lamp system upgrade with high-power bulbs.
As always, check the wire sizes for capacity before you make a big upgrade. The stuff in my headlights doesn’t look to be big enough for extended 140w service, especially in warm weather. A few users have suggested adding separate power feed and relays for the lights, a task made convenient by the power cable terminal in the engine compartment. Users should also keep an eye on the total electrical loads in the car. Running the big 140w main beam lights on top, with 100w aux main beams on in the bumper, in the rain with the AC running and the high power stereo playing… Check your alternator’s rating and consider the derating factors with low-speed driving and high ambient conditions. Got Juice?
dr bob
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Headlights Won’t Go Down
In question dated: 11/10/00
The car is an ’87 and I’ve never had any headlight problems before. I went out tonight and when I got to my destination my headlights did not go down. They turned off but would not fold down (and yes, the car was still turned on). On my way home I noticed that they were pointing a little skyward. Maybe that’s why I was flashed three times. While driving I flicked them off then on, and once again all was normal. When I got home they retracted just fine. Any helpful hints? What could be loose?
Thanks
Doug
In a response dated: 11/11/00
Could be an electrical problem – that circuit is VERY complex! – or could be mechanical. Check th tightness of all of the fasteners on the retraction mechanism, etc.
As an aside – it bears repeating that there is a possibility of a potentially serious problem with the headlamp linkage on ANY 928.
Open the hood (bonnet to some of you). Look in front of the radiator/condensor on the left side of the car (the right side as you are facing the front of the car) and locate the headlamp retraction motor, which is a rubber-covered cylinder about the size of a drink can. Attached to the motor is a crank, and fitted onto that crank is a flat linkage bar that runs down to the headlamp actuation bar. This flat link bar should be retained at each end by a metal clip, commonly called an “E clip”, from its shape.
If the top E-clip is missing, the headlamps could unexpectedly retract at any time. That could ruin your night!
If the bottom E-clip is missing, the same thing could happen. In addition, if the link bar comes off and you then turn the headlamps on, the link bar can very easily be driven thru the A/C condensor and radiator, destroying
both.
Either result is drastic and expensive, and one is potentially fatal. Quite a reaction to a missing fifty cent clip!
I would suggest that you consciously form the habit of looking at the clips every time that you open the hood.
Wally Plumley
928 Specialists