Lionel S4 - 88

Hello again ... wrong key pressed

Am also a fresh new french owner of a Porsche 928S4 (MY88, AT) , just imported from Japan .

The same fuse for both internal lights and reverse back-up light is getting burnt after 30 seconds when 7A , or 2 minutes when 15A .

During the short time the fuse survives , all works well , interior lights and reverse back-up lights .

Have tried to disconnect some interior lights , not yet all , same issue .

Tried another back-up light block coming from another S4 , seemed ok for a while but the fuse burnt again after few minutes when I reconnected the interior light of the driver-door .

Short of fuses , stopped trials .

Will re-proceed deconnecting all interior lights .

Was wondering if it could be either a short-cut in the back-up light block ?

Regards

dr bob

Lionel-

There's a common problem that is related to the wiring above the lamp above the windshield. Wiring rubs through there to ground. DO NOT substitute a 15a fuse even for diagnosis. Thw wiring is small and will melt even worse if there's a short, and there obviously is in your case. Follow the directions above: Disconnect the battery ground, then remove and inspect each of the lights carefully. Pull a little of the slack wiring with the lamp and inspect for burns, arcing damage. Repair as necessary. The lamp assemblies are rather primitive pieces, carryovers from the early VW and 911 days at Porsche. You need to tave extra care when handling them even for simple tasks like changing a bulb; One false wiggle and you ground an exposed connection to the car body, blowing the fuse.

WallyP

"I also do not understand (as said I am not a proficient electrician...) if by "bridging" the connector and managing by this to lighten up the reverse lights and the R gauge on the instrument panel (as the mechanic claims he did) one by-passes the burnt fuse... I doubt this "

That makes it almost certain that the problem is in the switch. Cleaning or adjustment MIGHT take care of the problem.

Lionel,
A useful tool for finding a short circuit:
- Take one of the blown fuses and cut away a little of the plastic around the tiny metal tabs on the face of the fuse (where the number is).
- Solder two insulated wires to the connections of a small 12 volt light bulb, such as an instrument panel bulb. If the wires are 0,5 m or longer, you can put the bulb where it can be seen more easily while you are testing.
- Install this bulb in the circuit that is blowing the fuses. Have everything on the circuit off or disconnected. If the circuit is powered through the ignition switch, turn it on. (The interior lights don't need this.)

With everything off or disconnected, there should not be any current flowing through the circuit, so the bulb should not be glowing. If there is a short circuit to earth (ground), the bulb will glow. The bulb limits the current to a value that will not burn any wires or cause any damage. When you remove the short circuit, the bulb will go off.

vsalvato

I did check this morning and all the iterior lights work perfectly; therefore the fuse is not the culprit and the only option left is the Neutral Safety Switch to replace! My only hope is that 1) I find a repalcement part quickly and 2) this is not a too difficult task for my mechanic. Tks for help, in any case, excellent responses...

belgiumbarry

that's coincidense... replacing my transaxle seemed the backup switch was broken. I replaced it with the "old" one. ( '82 to '88 swap)
seems the same , only the push tip is more "shaped" on the newer model. It's only a loose steel rod , so i could reuse the new style one with the old switch.

Attachment 331492

SharkSkin

Barry, the switch on the later AT cars makes the ones on our MT cars look like a stone axe. See the pics in the thread I linked in post #6 above.

belgiumbarry

who the f*ck drives a AT car ?

SharkSkin

A few people, apparently.

vsalvato

Belgiumbarry, it may sound strange but even some italians today have converted to AT; besides the fact that both my every-day cars are AT since several years in my case when I screened a few 928's to buy I was suggested to consider AT rather than manual because: the AT mounted on 928 is from DaimlerBenz and amazingly reliable (x-fingers...). AT, is also supposed to prevent abuses on the engine and sporty style drive typically adopted with manual transmission. When you buy a 20 yrs old car with 100 Thousand miles and more this counts...

belgiumbarry

sorry vsalvato, just kidding... on the contrary i never had a AT and never won't... i have now 6 cars.. all MT... just a obsession..
My daily now is a BMW 650 which i bought last year and the factory via the dealer ! was requiring if i was "right on my mind" choosing a MT... i told them who the f*ck must drive it the next years... ..so yes, i have probably the only one in Belgium...

Alan

On an '88 there are actually separate fuses for Interior lighting (7 & 24) and backup lights (12).

Which one is giving you issues?

NB Fuse 12 also supplies the mirror controls
Fuse 7 also supplies some dash lights/diagnosis connector
Fuse 24 also supplies the diagnosis connector

Alan

vsalvato

Alan, I guess your question is for Lionel? As to me do not seem to have problem with any the fuses; they all seem to be ok, interior lights are all OK, the mirrors adjustment also OK but still the reverse lights do not work and so the R gauge on the instrument panel. I will get the mechanic to replace the Neutal Safety switch tusting that this is the last option to try.

vsalvato

Barry... no problems, I kind of envy you for your 650 and indeed it must be the only one around in Belgium. I did enjoy most of my past cars with manual gears; I was so keen that I ended up owning half a dozen of off-roads with plenty of gears and fun. But as time goes by I ended up changing my driving style as I drove many hundreds of thousands of Km (and a few thousands inBelgium too, back and forth from Zaventem to Waterloo and Charleroi, and ended up losing some of the faith with it. Now I like driving more relaxed and lazy, hence AT!

belgiumbarry

getting old vsalvato ? ............

ROG100

Just bringing this one back to the top.

I have the same problem on my GTS and so does another local on his 87 S4.
We checked all the usual possibilities with no success.

On my GTS the PRND lights were intermitant with no logic to the failure.
The reverse lights did not work at all.
My conclusion was the neutral safety switch. Changed it out with the correct Porsche one.
So far the lights on the dash now work all the time but still no reverse.

Any other ideas?
Roger