blandis

Having issues after stereo install.

Head unit was working, now is not. Happened after we pushed unit in all the way in. Thought we were very careful, but realized the wire on my new unit (yellow) that is hooked to the small red wire from the harnees got pinched and most likely shorted out. It has a cut and was bar. But it blew no fuses in the fuse panel.

I now have no power from the white or small red wire out of the factory wires. Larger red wire is hot. Again, no fuses blown in the fuse block.

Door chime never worked before we put this new stereo in, replaced a JVC cassette head unit. Now it does.

Here is where things get weird. Door chime works as it should when key is turned on, doors open, etc. Volume and frequency are normal. Once started still chimes but is very muted, and really can only hear it if setting still as it is not very loud. Same frequency as if doors are open. Sounds like speaker blown and it "volume' is very low.

If you turn parking or headlights on it chimes a bit louder, but frequency slows down (does not chime as fast).

Another strange thing is if you turn the interior light on between the visors, it will affects the door chime. It clicks three ways, toward windshield, middle and towards rear hatch. If you click it towards rear hatch door chime comes on at full volume as it does when doors are open or key is just turned on. Same frequency and volume.

The interior lights in the doors now do not work at all, regardless of what position you switch them to.

Dont notice any other issues with anything else.

Oh, the MB 210 Quartz install was fairly easy in the doors. Funny how I thought this was going to give me fits while the head unit was going to be the easy part.

Only other things I did was to tap into the wire on cigarette lighter for the illumination.

Appreciate any help you guys can give me.

WallyP

When wired correctly each of the interior lights has a three-position switch:
- OFF Light does not burn regardless of door or hatch opening.
- ON Light burns regardless of door or hatch opening.
- AUTO Light burns when door or hatch is open, goes off after closure.

The red warning lights in the door edges should go on when a door or the hatch is opened, and go off after closure. There are no switches for these lights. (This makes them a prime suspect in cases where the battery is being discharged.)

The interior light above the rear view mirror is notorious for having shortages in its wiring. The red power wire tends to short circuit to the body metal. This can cause problems with the interior lights and the instruments.

The normal power wiring for the sound system head unit is:
- Brown: Ground (Earth) connection.
- Red/Black: Main power. Fed from ignition switch (15 Bus) thru noise suppressor (looks like a small transformer) and sometimes thru an in-line fuse.
- Red (Usually): Memory (constant) power. Source varies by year, but for you is probably shared with the hatch opening system from F4.
- White: Antenna trigger.
- Black/Blue: Instrument lights. Some aftermarket units allow connection to a dimmable source for the display light.

You have probably either lost one of the power sources, or have a wire connected incorrectly.

blandis

Wally, thanks.

i have lost power to the small red (memory constant power) and the white (antenna). Rear hatch does not work either? That interior light between the visor also does not work, but will change the door chime still when switched.
What is F4? I assume I blew something somewhere, but sure cant figure out where.

All interior lights and hatch worked fine prior to stereo install.

dprantl

Are you absolutely sure your fuse for the radio/interior lights is good? This exact same thing happened to me when that fuse blew (both my former '86 and my '91). Maybe replace with a known good fuse even if it looks ok?

Dan
'91 928GT S/C 475hp/460lb.ft

blandis

dp it looks good.... have not tried changing it.

will when I get home and test it out.

Alan

This is an interesting comment.... there is no central electr8ic panel fuse for the radio on any model year. There is one on the back of the radio for some models ('84+) and some <'84 models have optional inline fuses near the (optional) supressor - however most have exactly nothing... ergo: the wiring is unprotected.

The radio mounted fuse does nothing to protect the head unit wiring - its most likely you melted a wire if it shorted out...

Based on your symptoms I'd guess you melted a ground wire and that is causing interaction issues on other circuits.

Fix the interior lights first so they work (the hatch release is related to this and will likely work when you fix it) this may just be a fuse...

Open up the console - take the side panels off & radio out and see if you can see what burned up... look for an inline fuse at the same time.

Screwing with the radio on these cars is risky - Porsche seems to have virtually booby trapped them...

And yes I really do mean it - there is no CE fuse for the radio

Alan

WallyP

The power on the white antenna trigger wire is supplied by the radio, and if the radio doesn't turn on, there will be no power on the white wire.

F4 is the plug terminal where the red constant-hot wire usually connects. That is, Terminal 4 on Plug F at the bottom of the Central Electric Panel. This terminal is fed thru Fuse #23. Check this fuse and its connections very carefully.


As Alan says, there are a surprising number of circuits on the 928 that are totally unprotected. Porsche also has a habit of putting switches on the ground side instead of the power side sometimes.

blandis

Alan, I have it all open. I put inline fuses on every wire. Problem is with the yellow one that got knicked (not sure if it shorted or not) but did so between the fuse and the head unit.

Any idea of where to start looking.

Why would both the small red and white power wires go dead at the same time?

blandis

Thanks Wally.
Headed home know to torture myself for a few hours and try to figure this out!

Alan

What wires do you have connected to what - the Red/white on the car is usualy not a small wire by any imagination..?

The only car wires you need for power are a solid Ground (brown), a switched power (Red/White) and a constant Power (Red) - everything else is optional... as Wally says the radio supplies some things - anttenna power, amp turn on signal etc.. and it may want illumination and speed inputs but these are not critical to getting it to turn on.

The Red/White switched suppy comes from the ignition switch via the supressor on your car - the supressor should be below the radio on the drivers side and look rather like a transformer with just 2 wires.

There probably is no stock red wire on an '84 - so who knows what may have been spliced into if this had previously been provisioned by an aftermarket installer!! - look around the CE panel for a splice (possibly the interior lights based on what you saw?). However you can link to the battery power bus bolts on top of the CE panel and use an inline fuse instead.

Alan

dprantl

Hmm, interesting. On my '91, there is fuse #21 labeled "Radio - Amplifier". When I remove this fuse, my head unit gets no power. I was just messing with that fuse a couple of days ago. I don't remember exactly what it was on my '86, it was a few years back.

Now that I think about it more, it may have been fuse #24 on the '86 (Current Pulse-Tailgate, Interior Lights). With that fuse removed, the head unit would not power up, the interior lights and rear hatch release did not work, and the door chime made funky noises with the car started. On the '84 it seems that this fuse is #23 as Wally mentioned above.

Dan
'91 928GT S/C 475hp/460lb.ft

blandis

Attached is a pic of how its wired up.

Im working on checking fuses and wiring.

blandis

dp wally and allen.

was fuse in 23. The fuse looks fine, but must have somehow went bad?
Swapped it for one from the high beams and everything works fine for now.

Yellow wire which is hooked to battery (constant power) red wire only has a 1 amp inline fuse. That to small?

For now working. Im going to take my time and put everything back in slowly.

You guys saved me hours of searching. Lesson here is to test the simple stuff regardless of how it looks.

Owe you guys a cold one.

dprantl

I knew it was the fuse. Glad it helped you narrow the problem down so fast.

Dan
'91 928GT S/C 475hp/460lb.ft

Alan

The radio amplifier fuse is for the amplifier only... some tap into this for the constant power (thats what it is). Most years don't actually have this provisioned stock (though it may have been added already)

The switched supply never has a fuse on the fuse panel & this is what every year has.

With the amplifier not connected you won't get sound obviously - some head units will power up without constant power - most probably not so if thats where constant power was tapped into it may make sense... but its not stock wiring

Alan