[Jmartinez737]

I have a 72 chevelle Malibu ss clone v8 350 small block and I'm having serious problems! first of all when I turn on the car the front lights work but none of the back lights do! tail lights, break lights, reverse lights, signals ect... But when I turn the car off and even take the key out one side back light and the tail lights turn on! I know it makes no sense! Everyone I ask doesn't know why it's doing that and I know nothing about wiring or how to fix this problem! I searched online for diagrams but found nothing! Does anyone know what's going on? or have any tail light wiring diagrams that can help me? I would be sooo grateful!!

Thanks, Josh

 

[blm]

I would start by tracing it backwards. The lights work at some point so the wire bundle is not damaged or cut/broken. The rear harness runs from under the dash,under the drivers side and al the way back to the lights. If you pull the carpet back under the drivers side and up near the firewall you should see the rear wiring harness in the vicinity of the brake pedal. I would check the under dash connector for the rear harness and see if it is loose or perhaps has some corrosion ( that you would have to clean off) or damaged somehow.If you don't find anything there keep going backwards. A multimeter is an invaluable tool when diagnosing electrical problems and not just for cars either they can be used for anything electrical.

 

[Gary56]

I don't know if this would help, but I can tell you what those things have in common if it were on a '67 which is what I have. Mine's been altered somewhat by previous owners to boot. There's a red wire that goes from a block in front of the battery to the horn relay. If it still had an external voltage regulator, that would be in route also. From the horn relay, the red wire goes to the top inside port on the outer bulkhead connector (mine has 2). From there it goes to the headlight switch, and from there every where else you're having problems with. I would do what Brad says starting from the front and working my way back to see where you're loosing it. That red wire to the bulkhead and then to the light switch is what's in common with your problems. Once past the light switch there isn't much in common with all those things except maybe the ground. Start with something obvious like fuses and their continuity. My wild arse guess would be a bad connection at the bulkhead, but that is a way out there wild arse guess, especially since you don't even have the same car as I do. The key off lights on deal is usually a back feed to ground from somewhere due to an open circuit. Makes no sense to me, but that's what I've found in the past. BTW, there's a person on ebay that sells laminated color wiring diagrams for old cars. Good luck.

 

[Jmartinez737]

Thank you soo much brad I'll try what u said and update what happenes! And gary thank you soo much as well! Sorry a few dumb questions what is a bulkhead and what does it look like also what is the block and how can I find the block that leads the red wire to the horn relay also what and where is the horn relay?

 

[Gary56]

Thank you soo much brad I'll try what u said and update what happenes! And gary thank you soo much as well! Sorry a few dumb questions what is a bulkhead and what does it look like also what is the block and how can I find the block that leads the red wire to the horn relay also what and where is the horn relay?

The bulkhead connector is where the wires pass through the firewall. It's on the left side below and to the left of the master cylinder. On my car, there are two plugs side by side, about 1" wide and 3" or so long. The fuse pannel is on the other side of those plugs on the inside. By 'block' I'm refering to a post where a hot lead attaches, and other wires take off from there, often times fusable links are there. On some cars,they're located in front of the battery on the radiator core support. Some cars it's located on the firewall. Some cars it's located on the inner fender.