Brake light problems

[barnesjtsl]

79 Spider 2000 carburetor.

Every time I hit the brakes fuse A blows?

Also, there is a red wire with a blue stripe on it with a push connector at the end coming out of the wiring harness where the wires for the rear lights board are. It isn't connected to anything and I can't see anything to connect it to. Any ideas?

There is also a black wire coming from the same location that looks like a ground wire. But when I connect a test light to it and touch the positive side of the battery, no light, so no current flow.

Any thoughts?

[18Fiatsandcounting]

It sounds like you have a short somewhere. The wiring for the brake lights is pretty simple: Power from Fuse A goes via a white wire to the brake light switch on the brake pedal, and from there it goes via a red wire to the left and right brake lights.

To minimize the number of new 8 amp fuses you'll need to buy, I'd start with removing both brake light bulbs and both connectors to the left and right assemblies. Step on the brake pedal. If the fuse blows, then the short is at or near your brake light switch. Then reconnect one light assembly, test again, then the other assembly, test again, then put in one bulb, test again, then the other. The point at which the fuse blows indicates where the problem is.

As for the red/blue and black wires, I'm guessing that these are for the power antenna if you have that feature on your radio?

-Bryan

[barnesjtsl]

Thank you VERY Brian. I'm finished for the day, but I will try those steps you outlined tomorrow and keep my fingers crossed.

I will post results.

Thanks again!

[DieselSpider]

I cheated and just ran a new wire to the brake lights from the switch on the pedal along with provided power to the brake switch from a different fuse since even though the fuse wasn't blowing it would cause the fuel valve for the Injector Pump on the Diesel to close stalling the engine. What made it harder was that it did this intermittently while driving and never while trying to chase it down at home. Of course it would only do this during heavy rush hour traffic on the commute to work.

The wire from the brake light switch runs from the pedal to under the carpet to the left of the drivers seat and then over the wheel well in the trunk.

[spider2081]

Have you inspected the physical condition of the red wire on the brake light switch. It might be pinched by the pedal movement. If it looks ok un-plug it from the switch,then press on pedal if the short is in the wire or a light assembly when the wire is disconnected the fuse will not blow.

[TX82FIAT]

Agree with some of the prior posts that the previous circuit has a hot to ground blowing the fuse. Since it occurs when driving I would suspect an area/location where the wires in that part of the harness rub against a metal surface based on your movement, the location of the wire or high vibration making contact at the right spot to ground out blowing a fuse. May be worth tracing the circuit to see where the worn wire or wires exist to prevent possible future issues with other wires that may cohabitate the area. Replacing a span of wire and insulating in a loom is a pretty quick fix.


Electrical gremlins can be a bugger on these cars. Once well sorted and maintained, original circuits will function as designed with proper amps at proper times. Makes for a more enjoyable experience and future problem solving that mostly resembles a factory wiring diagram.

[barnesjtsl]

So. Fixed. It was the ground wire on the Drivers side circuit board. I will never try and trouble shoot electrical again with out cleaning up every ground!

Thanks for all the help.

[spider2081]

. It was the ground wire on the Drivers side circuit board.

I don't think a poor ground will make a fuse blow, It can prevent the light from lighting or cause it to be dim. Is the bad ground all you found??

[barnesjtsl]

Sorry, I should have also mentioned that the light board on the passenger side was bad. I had originally though my old one was bad, but the second had one I bought on ebay turned out to be bad.

[spider2081]

the second had one I bought on ebay turned out to be bad.

I have seen some tail light PC boards that appear "new" the have a manufacturing error. There is an extra PC land between the light power and ground. If you carefully inspect the new board to the original board you might see the issue I simply drill a hole through the undesired bridge to remove the short and then the board works fine.