I am having problems with the taillights on my 65 Cutlass. The taillights are on when the headlight switch is off and go off when the switch is pulled to the on position. The stop lights don’t light up either when I apply the brakes I removed the headlight switch and bench tested the switch and it checked out ok. I have a CSM and will looking at the wiring diagram. Is there anywhere else that I might have to look to troubleshoot the problem?

 

Hello I had problems with my 65 also. Start by looking for alterations to the wiring and check the operation of the brake switch. Should have power at brake switch. Taillight problem I’m not sure, but I think I would replace the switch to be sure. Do the turn signals work correctly?

 

No alterations to the wiring, I’ll check the brake switch. Turn signals not working correctly but that is due to adjustment on turn signal switch.

 

When the tail lights are on are the instrument panel lights on also? Have you determined specifically if its the tail light filament or if its the brake light filament? In other words do you have power on the green or brown wire?

 

Lights, brake lights, turn signals all tied in together and go thru the turn signal switch.
Check one system at a time. There is no adjustment on turn signal switch that I’ve ever seen.
Light switch can check out ok and still be bad. It is 55 years old. I had a similar problem on an el Camino.

 

Taillight filament ok, brake light filament not working. Intstrument lights working. There is an adjustment on a tilt wheel turn signal switch that is located on the lower end of steering column. How would a light switch be bad if bench tested to be good? I have power coming from each connection on the switch.

 

The tail light circuit doesn't go anywhere near the turn signal switch. The only place the tail light circuit and the stop/turn light circuit touch is at the 1157 bulbs where the two filaments share a common ground. A bad ground can cause all kinds of havoc in these two circuits.

 

Is this a problem that just started? If you unplug the headlight switch do the tail lights go out?

 

I second the bad ground. A 55-year-old vehicle needs all grounds renewed...or as many as you can find short of a full tear down.
Did you pull the tail bulbs and inspect the sockets?

 

I don't see how it can be a bad ground when the light come on with the headlight switch off...?

 

Does the taillight socket need to be plugged into the housing to be grounded? Maybe this is my problem. I have the sockets out of the housing while I’m observing the problem. I think the turn signal problem is an isolated problem.

 

If there is no 3rd wire yes.

 

yes , the housing is the ground for the socket normally.