Classic/Antique Car Repair: Inoperative Brake Lights, brake light switch, pontiac bonneville

Question
QUESTION: Hello,

I recently purchased a 1964 Pontiac Bonneville Convertible in great condition.  The only problem that I am having is that the brake lights are not working properly.  Last week, I corrected the problem, perhaps by dumb luck, when I removed one of the bulbs, reinserted it to ensure a good fit, then put the housing back in the hole which also acts as a ground.  Yesterday, the brake lights disappeared, and I am having a tough time identifying the culprit which I believe is a poorly grounded socket.  By the way, the fuse is good because it also operates the tail lights which function well.  Thank you for helping me solve this annoying problem.

Vince

ANSWER: If both brake lights are not working, but your turn signals are working correctly front and back, the problem is not a grounding fault at one of the sockets.  If both brake lights don't work, try bypassing the brake light switch by unplugging the wires on the switch and connecting the two ends together - that should make the brake lights light up.  If that occurs, inspect the brake light switch- if it is the mechanical type it may simply be out of adjustment, but if it is the hydraulic type (screwed into the brake fluid lines), it has probably failed.  These are cheap and easy to replace.

On the other hand, if only one bulb doesn't light when it should, that could well be a grounding problem, as you suspect.   Unfortunately, sockets were not supplied with a separate ground wire on older cars, so as the sockets build up a layer of oxide between the bulb receptacle and the tail light housing, this sort of problem is very frequent.  The sure cure is to solder a ground wire to the bulb socket and run that wire to a known good ground point on the car's body.  Sometimes you can fix the problem temporarily by just cleaning the socket and the area where it is crimped into the housing, but usually the problem returns on the first damp day or large bump.

I hope this is of some help.

Dick

---------- FOLLOW-UP ----------

QUESTION: Dick,

Thank you VERY MUCH for responding to my brake light issue, and for the good advise.  Before I received your response, I decided to remove each bulb, and inspect for any corrosion in the socket. Everything was very clean.  I even noticed that the metal "ring" that is in the plastic housing and that the bulbs sit in were snug against the bulb.  One or 2 seemed loose, so I crimped the ring a bit so that the bulbs would fit more tightly (that could have been a mistake...read on). When I reinserted the socket/housing back in the hole, at times the bulb would go out, and I suspect that there might be a loose connection.  
By the way, there are 3 bulbs per side. Before I began this excercise in futility, both sets of turn signals functioned properly, front and rear.  Now, the right signals work fine, but when I put on my left signals, all signals, front and rear, flash!  Without doing much, I seemed to have exacerbated the issue. I also noticed minor moisture under the trunk mat (it is a convertible, and I gave it a quick wash the other day).  Perhaps the moisture, as you suggested earlier is the culprit.  Do any of these clues/symptoms help in th diagnosis?  Once again, I truly appreciate yourtime and efforts in assiting me.  Oh, one last thiong, I noticed wahat I suspectto be a ground woire running from the trunk, near the lights, and connected to the rear light wires.  There is a metal grounding clip on the lead which I assume should be clipped to a portion of the metal body...which I did...but that didn't cure my problem.

Vince  

Answer
Yes, this points us directly to the problem - the one rear light that does not work has a socket that is not making contact with ground.  If you set the left turn signal to blink, and then touch a grounded wire to that socket metal, you'll see that it will begin to work correctly.  Also, if you set the right side to blink and touch the wire to the socket of the left side bulb, you'll see that the right side begins to work correctly also.  

What is going on here is: Because of the missing ground on the left brake bulb, the return current from the left brake filament has to find some other path back to ground - and the only one available is through the common filament (the bulbs have two filaments, one for running lights and the other for the brake/turn light) which makes all the other bulbs in the circuit light up.

You will have to solder a ground wire on that left brake light bulb socket, and route it to a known good ground on the body.  

The crimped grounding provision for the bulbs was a cheap way to build the cars, back when no one imagined that these cars were going to be on the road for more than the 5 year average life in those days for a car.   

The expensive cars had ground wires, and silicon grease around the bulb bases to prevent corrosion, but all the lower priced cars took the same shortcut.

These days, with the much longer life expectancy for cars, and the increased use of plastics for light housings, all cars have the ground wires, at least the ones I am familar with.

I think this will solve your problem.  The other bulb sockets will probably need this fix sooner or later too.

Dick