'81 put in reverse and fuse blows

[rjkoop]

Yep. Electrical issues are a real pain.

Got the horn, hazards, turn signals and front lights working. Then, even while not running the car, I put the car in reverse to check the reverse lights and the 1st fuse (the one closest to the middle console) blew right away. This had happened 2x and I'd rather not blow another one.

I checked the connector that comes up through the center console and it's fine. And I cleaned and checked the grounds everywhere else including the rear light housings. Would this problem indicate a missing ground from the transmission to the engine body? My car was missing the bottom bell housing inspection plate and I think others have mentioned this is where a ground should attach.

Or maybe I could check where the wires attach to the transmission under the car.

[spider2081]

The back-up light switch is located on the passenger side rear area of the transmission. It switches power to the lights. It is very common for a wire to brake off the switch and short on the metal. Symptom is blown fuse. You have to craw under the car one more time.

[rjkoop]

A bit more info. I raised the car and looked at the connector on the rear of the transmission. It's fine. Not frayed or broken at all. The ground on the transmission is solid as well. I even disconnected the connector on top of the housing (inside the car) and used a multimeter to test that when I put it in reverse it connects properly and it does.

On a whim I disconnected all the rear light plugs from the housings, put it in reverse and the fuse didn't blow even after 10 minutes or so. I'm thinking there must be a short somewhere on one of the rear light circuit boards. I'll diagnose closer with my new multimeter ($24 on sale at Cdn Tire right now! Great device).

[spider2081]

I made an inline fuse holder with alligator clips on each end so I can use standard automotive 3AG fuses for troubleshooting. I remove the stock fuse and clip in the test fuse.
Is the fuse that blows 8 amps?? That is the value for it in my owners manual
If you don't see anything wrong with the rear light boards
I would put the left bulb in and see what happens. The rear light assemblies should operate out of the plastic housings.
The back up light switch is different part with Automatic transmissions than with manual shift.

[rjkoop]

So I think the issue is with the passenger side rear light circuit board.



I used a multimeter and noticed that 2 of the wires on the large connector on the right (2 ones just to the left of the far right one) shorted out. I couldn't find where they would be shorted and they are feeding the light on the top right. The 2nd one in from the right looked a bit singed as well. I tried sanding the areas in between the current tracts (not sure of the term) and sprayed with electrical cleaner but didn't make a difference. Also I ensured that the contacts for that light weren't touching each other.

Can this be repaired somehow?

None of the connectors on the driver's side light circuit board shorted out so I think that one is ok.

[4uall]

Richard, I have extra tail lights if you are interested in swapping them to see if that is the issue

[spider2081]

Is there a chance the center contact on the light socket is touching the outer ring? When the bulb is in that contact is pushed down quite a bit. The board looks pretty good to have a short in it.
If the problem is in this board the drivers side light should work with this board out of the car

[rjkoop]

Richard, I have extra tail lights if you are interested in swapping them to see if that is the issue

Thanks Jay. I'll let you know if I need them.

[rjkoop]

Is there a chance the center contact on the light socket is touching the outer ring? When the bulb is in that contact is pushed down quite a bit. The board looks pretty good to have a short in it.
If the problem is in this board the drivers side light should work with this board out of the car

Nope. It seems to bend up at the correct angle and no contacts issues. The short is definitely on this board so I think I will try the reverse light with the driver's board in. I think it will work fine.

There's got to be something on the passenger circuit board shorting out. I just can't see it.

[spider2081]

It is a strange one. Usually the boards suffer from open circuits or intermittent circuits because of loose rivets
please let us know your progress.

[rjkoop]

Got it. When I looked at a sharp angle under the light socket part I noticed a connection between the 2 parts of the socket. Must have dropped off an old bulb or something and 'welded' in place.

Once I scraped it with a small screwdriver the short is gone!



Thanks all for your help.

[spider2081]

Good to hear it's fixed.

Enjoy your ride

[RRoller123]

another gremlin put to rest!

[rjkoop]

Got 100% of the lights working on the rear driver's side. No lights working on the rear passenger's side panel though!

I checked the connector from driver to passenger lights and I get voltage on the passenger side at the right times for lights, blinkers, reverse and brake. This is when I use a multimeter on the passenger connectors... + lead on the individual wires and - lead on the ground wire back on the driver's side. Should I see 2 wires at the ground post in near the driver's side light housing? I see a black and a white/black screwed into the ground post. I'm wondering if the PO had issues and started moving wires around.

I'll take a closer look at this...

http://www.artigue.com/fiatcontent/Wiring_1980_1982.pdf

I should be able to figure this out.

[spider2081]

The white/black wire should be the electric fuel pump ground. So yes there should be 2 wires one is the light assemblies ground and the other is the fuel pump.
One of the only complaints I have with the Fiat wiring is the harness that connects the rear light assemblies. I wish the wires carried a color code. Having them all yellow makes trouble shooting more of a challenge. I think you are missing the ground for the passenger side and that ground is made through the drivers side board. I think it's the third pin from the top on the PC board in your last photo ( center next to double pin). On the drivers board it is pin next to double pin near center. The Main connector connecting the driver side board to ground is on the center pin.
The short on the passenger side board might have damaged the drivers side PC board. I would inspect it first.