1984 Nissan 720 Brake lights not working.

[Josue Flores Jr.]

I have a 1984 Nissan 720 4x4 king cab, and I'm having a brake light issue. My brake lights turn on and work with the brake switch, but they seem to be dim on both sides. You can really only see the brake lights light up when my actual amber and head lights are off. If my lights are on, then you can't see the brake light flash to let drivers behind me know that I'm braking. So for about a week now, I've been driving with my lights off, that way my brake lights are at least visible. I've tested the brake light switch wiring harness plug thing, to see if it's getting power, and it does when the lights are off, like only on one side of the harness it's getting power, which in the other is just the ground connection. But then when I go turn on my light switch, it seems to pass current to both little pins inside the brake light harness. I feel like It's a ground wire that's bad, or some sort of short circuit that happens when I go turn on my lights. I've been trying to figure this out for about two weeks now, and I need to have that fixed to pass inspection. 

 

One more thing, I replaced the brake light wiring harness because both wires that connect to the brake switch were frayed. If anyone has any ideas or suggestions to help me figure this out please let me know. Thank you.

[datzenmike]

A short is a connection from power to ground around the actual load, be it a light, wipers fan etc. A short will draw infinite power and because all wiring is protected from this, it will simply blow the fuse.

 

 All wires at the back share a common ground so it would affect all lights f the ground was poor.

 

Lets do the easy stuff first...

 

FIRST and more important!!!! Check the rear tail light harness and the exterior body harness under the bed to see if someone has tried to splice or remove a trailer towing wiring harness into the truck. If there is evidence of this it's 100% that this is the cause.

 

 

 

Go to fuse box and swap the 3rd and 4th fuse from the far right hand side. Can't trust looking at the fuse. Did this get the brake lights brighter? If yes replace the fuse that was in the 4th position with a new one.

 

If no change...

 

Measure the voltage at the foot pedal switch. Check both sides. This from from the 4th fuse so it should be good. The switch connects when the pedal is depressed. Everything normal so far??

 

Outside... Find the round 6 wire connector between the rear harness and the exterior body harness, at or near, the right rear tail light.  The brake light power is Yellow/Red. If the connector is making bad contact just unplugging it and plugging it back together may fix the problem.

 

If voltage is low move forward to where the exterior harness passes through the body and connects to the cab harness from the brake pedal. It's a 14 pin connector located under the passenger side seat. Yellow/Red on the exterior harness side and Yellow/Blue on the cab harness side.

 

By now you should have found a problem that is fixable.