550 wiper, fuel lid, brake light failure

Hello, long time lurker first time poster here. As an introduction, I bought a German spec 1998 550 sight unseen with almost no planning during covid; a few years later, I am fully up to speed on international car shipping, sticky buttons, and removing and reupholstering a dash!

After a prolonged storage time (a year), I installed a new battery and everything works except the wipers, tuel lid, and brake lights. All run off the same 20 A fuse (number 4), so not a coincidence. Unfortunately the fuse is still good -- I tested with a multimeter. This leads me to suspect the fuse board?

But other than a visual inspection, I'm not sure how to debug a fuse board. Should I check connectivity between the power in and an output pin on the bench?

Any help appreciated, and thank you in advance!

 

Are you getting power (12 volts) at either end of the fuse? If not, check that there is continuity between the key relay "N" (pin 87) and the fuse.

If you have power at the fuse, check to see if you also have power at pin 1 of plug J.

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Current path:
Relay N pin 87 >>> bottom of fuse 4 >>>> top of fuse 4 >>>> plug J (pin 1)


The inside of the panel will look something like this:

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Check the soldering of the fuseholder and plug J pin 1. The relay soldering should be ok, because it also feeds lots of other components (and they are ok).

 

Actually, the photo of the internal circuit board may be flipped horizontally. Relay A should be in the top right hand corner of the photo:

Corrected, but I haven't flipped the plug and relay lettering... it would look too messy.

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I can confirm power to the fuse and pin 1. I guess this must mean wiring after the fuse board? Where is the last common electrical connection?

 

Thanks for the update...

Good question. Unfortunately, Ferrari don't tell us where they put their splices. However, keeping in mind that the splice has to be at a convenient spot for all 3 devices, the issue can't be far away from the relay panel. Maybe no further than the front of the centre console (It has to split off here to feed the fuel lid button). But it will probably be hidden in a large bundle of wires. Power goes to both the steering column and the Wiper Module in the passenger footwell (for wiper control). Power also goes to the switch on the brake pedal.


I have heard of partial shorts on wiring which haven't blown the fuses, but if you are getting 12 volts at J-1, then it's less likely there is a partial short. Anyway, it wouldn't hurt to try to isolate the issue by disconnecting plugs. e.g. the plug on the brake pedal switch or the wiper module.

The wiper module appears to be under the dash on the driver's side.

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Actually, the wiring on a LH drive car goes up the RH side of the car first...

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So unless the issue is a partial short, the fault must be before the wiring bundles split into two.

 

When you did your wiring checks, did you remove the J plug to check pin 1 or did you backprobe the plug (with it fitted).

Could the pin on the harness plug be faulty? Is the pin properly located?

 

Ugh... Is the harness wrapped in black plastic sleeving or is it wrapped with Tesa cloth tape?

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Maybe you could try shaking or flexing various sections of the harness to see if it makes a difference?

 

I back probed the J plug with it fitted. Great idea to check continuity through the plug -- that's the next common joint in the system.

Assuming that works, and a physical wire issue is both relatively unlikely and extremely hard to find, I like the idea of unplugging things one by one. Something on the circuit is causing some kind of short.

What is the list?
- brake pedal switch
- 2x brake light
- wiper module
- wiper stalk
- fuel cap switch
- fuel cap solenoid

Did I miss anything? I won't have time until tomorrow to start experimenting.

 

Actually, now that I think about it, it might not be a useful diagnostic method.

It seems unlikely that the brake light (tail) wiring would cause the issue as the brake pedal switch sends power to them. e.g. The wipers should work if the brake pedal is not pushed (if there was a partial short on the brake lights). Actually, disconnecting the brake pedal switch wouldn't even check the power wire going to the brake pedal switch for shorts.

I don't have a wiring diagram for the fuel cap release, but if it's like the 456M, the power going to the solenoid/actuator goes through the switch. Again, the wipers should work if the fuel cap release is not pushed. And again, the short could be in the power wiring going to the switch (on the blue/black wire).

Anyway, try disconnecting the wiper module. There might be electronics in there dragging down the voltage.

But maybe your best bet is to buy a cheap wire tracker....

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... although they are not very good for chasing faults in large wiring bundles.

 

Most wiring is shown in this (USA) diagram:

https://www.dropbox.com/t/lP2Su5cLKYzHu7JK

 

Success! It was the J plug. A good wiggle and reseating of the wire into the plug got things working.

Thankyou for you help!

 

Phew... I love an easy fix.

Don't want to jinx you, but is there a possibility that it's the soldering under the J plug that is cracked? Wiggling the plug may be disturbing a dry joint. Anyway, time will tell.