Tallights and brake lights

[patrick66]

On the '66 Imperial, I'm having a devil of a time sorting out why the hell the taillights come on when the brakes are depressed, and the brake lights come on when the headlights are turned on.

Ideas??? I'm not seeing much in the FSM that is helping me troubleshoot this.

 

[Big_John]

Bad ground at the rear could do that. Switched wires at a connector is a possibility too.

 

[patrick66]

Here is what I've done so far to try to fix the problem:

1) Replace all of the bulbs
2) Clean the bulb receptacles
3) Spray those with electric grease
4) Fixed two frayed wires that had been hit by critters
5) Replaced the brake light switch under the dash
6) Checked the fasteners that hold the light housings to the body

I figure it's in the rear somewhere. The front parking lamps do NOT come on with the rear taillights when I hit the brakes. The RR turn indicator works, the LR does not.

It was about 100* in the shop yesterday, so I didn't spend a great deal of time on the car.

 

[65Newport]

I had that problem on an (excuse me) 65 mustang I restored for the wife and it was bad ground.

 

[rkrochen]

Definitely a bad ground. The power is looking to ground somewhere so it is channeling bad through the other filament. Try running a separate ground to the socket to see if it helps.

 

[patrick66]

This afternoon, I tried a couple of things, since I burned up my voltage tester yesterday by installing its 9VDC battery with reverse polarity! Toast.

I installed a new tag light socket and bulb, since the old one was pretty rusty. Since the blinkers were operating fast, I swapped the blinker relay with the one in my '68 truck. So, now I have a tag light and the blinkers have a slower cadence...but no change on the ground issue. I've also worked on the ground on the taillight panel, to no avail. Either all of them are brakes when the headlights are on,or the taillights when I hit the brake. All of the lights come on at the proper brightness, either way, so no one socket seems to be at issue.

 

[65sporty]

Bad ground at the rear could do that. Switched wires at a connector is a possibility too.

I am with Big John ck to make sure the wires are not switched

 

[68-300]

Any difference when the turn signal switch is set to left or right? Does it blink with the normal light or with brake light?
Haven't checked the wiring diagram but if someone worked on the turn signal switch and crossed the wires or the switch itself is shorting something like this could happen I think.

 

[Boomer]

I've seen shorts in harnesses do this. Could be moisture inside a connector, too. Can't recall the vehicle now, but I remember something similar happening with a fuse box. Water was getting in from a leaky windshield gasket, fender rust, something.

If other suggestions don't work out, I'd start working my way back cleaning all the connections and connectors (WD-40 works pretty well for this) to make sure they are making good contact. If it's not a bad ground or connector, you've got circuits cross-pollinating somewhere.

 

[polara66hardtop]

I have to admit your problem is Intriguing. I'm thinking about it because my 79' 300 does the same thing. Hit the brakes, keys off, the four way/Flashers on the fender, and running and brake lights around the car light up. I have been messing with the hazard flasher switch, and it comes and goes. Every other time it works right, then it does it. But, it is a newer car with the switch in the steering column.

 

[patrick66]

I'm going to try running two jump wires at the connection where the harness comes into the trunk and see what happens there. Run a pair of jump wires across to the opposite terminal for each wire. If the brake lights and running lights work like they should at that point, then there has to be a cross somewhere in the harness.

 

[polara66hardtop]

I remember rewiring a Superbee 30 years ago with this problem. In that case I had to replace the headlight switch. it has Power all the time, tail light and brake. Another culprit can be the dimmer switch on the floor. A dead short is possible, as the whole car body in a Mopar is grounded. I know it sounds dumb, but a friend of mine had the bulbs in the tail for a single filament, when he needed dual. He also had weird lighting problems.

 

[patrick66]

I've got an extra dimmer switch; I'll have to check that out. Takes about three minutes. Now, a headlight switch might be a problem to source. I have several headlight switches from A- & B-body cars I'd parted in the '90s - does anyone know if a Sixties B-body h/l switch will interchange with the '66 Imperial?

 

[polara66hardtop]

Chrysler maybe. I can't picture what it looks like. I have a parts book, so I'll see if the numbers are the same.

 

[patrick66]

According to the Rock Auto list, they show the same replacement switch p/n for 1966 Coronet, Chrysler and Imperial. If you can double-check your Mopar parts book for me, I'd be appreciative.

 

[polara66hardtop]

The 66 parts book shows 2586598 for coronet.2584928 for Plymouth,Dodge,and Chrysler. 2584929 for Imperial.

That last digit could be just the fact to separate Imperial, could be the same switch.I believe all will plug in, If you just had one to test it, to rule out the switch. That turn signal switch still bugs me. as I had to Install a new one in a 69' Dart In order to get the Brake and tail lights to work right. The power is in the steering column all the time. Have you unplugged the four way flasher, and then try the Brake lights? Then, unplug the brake switch, and try the tail lights? It might shed some light.

 

[patrick66]

I unplugged the four-way and got the same results, except no flashers, of course. Unplugging the brake light switch, same same. Getting around to the dimmer switch swap this afternoon.

I noticed that I have no horn...kinda wondering if that has anything to do with things. I plan on puling the steering wheel later, if the dimmer switch doesn't solve the problem, and check the horn switch and the t/s switch.

 

[jct]

it could be your turn signal switch (wiring)