OK, my tails/brakes have always been on the dim side, so I bought some 3 bulb inserts for them (this is a '68 coupe btw) thinking it was probably just the old orig reflectors not doing much to help that single bulb...

So I throw one side in, and wire it up temprorary style by just twisting the wires together to make sure it all works and I've got something weird happening:

When the parking lights are on, and I hit the brakes, they do not get much brighter, it's clear the "bright" fillament is lighting up, but the overall brightness isn't changing much. I'm also certain I have the right leads for the bright/brake side of the wiring...

I have the car on a charger to be sure it wasn't just a low battery, and same results.

Before I put in the second side of 3 bulbs, I tested each bulb independently on the first side, and noted that as soon as I connected any of the 3 new brake/bright light bulb leads to the hot brake light lead in the car, the other side / single original bulb would dim considerably, and neither side would be much brighter than the running lights alone.

Hopefully I've described this right, but does anybody have any ideas what could be happening?

The brake lights are relatively fine w/o the running lights on, so it will be okay during the day, but I'd like to fix this before I get caught after sundown in it...

 

Make sure you have a good ground on the side you are working on. If you dont it will find a ground through the other side.

 

I thought the same, the new units don't have a dedicated ground wire like the orig. harness did, they seem to be relying on the metal to metal contact to the orig. bucket and it's contact to the body panels thru the mounting hardware... kinda a wierd setup really in that respect, because it's gasketed so heavily that I doubt there's a ground at all... maybe I'll take them apart and drill a hole to attach a ground wire to and try that. at this point though, I've put in BOTH sides, with no supplemental ground, and it is behaving the same exact way... i dunno

 

OK, some addl info...

I ran both brake and parking leads from the lights to just the parking light power source, and it is tons brighter, so I must have a power source problem on the brake light power. I'm going to run a relay to borrow power from the parking lights, but if any of you have an idea aside from running a new power line for brakes, let me know! I'm not sure if the brake light switch could/would have a ground issue as well? or just be bad?

 

I installed the Scott Drake sequential tail lights with the 3 bulb inserts. I think they are proabably the same type of setup as what you have. I ran a seperate power wire for them.

 

Yup, these are the SD inserts, just no sequentials... I picked up wire and relays yesterday

 

Cool. Did that help any?

 

ok so I get my taxes back and picked my 95 GT from a friend for $1950. I drove it home with no radio. this is my first stang. well the fuel gauge is not working least of my worries right now. but I put a radio in it yesterday and now my dash lights and night time running lights don't work. headlights and interior light still work. b/f u say fuses I already checked and replaced any and all fuses that were blown or messed up. and still no lights on dash or at rear of car when headlights are on. HELP

 

Make sure you didn't wire the tail light circuit up to the brake light side of the inserts. That would cause exactly what you are talking about.