p518

So, many years ago, I put a fiberglass bumper on my '72 Supreme car. After I discovered the parking lights weren't working, I put a ground wire from the back of the parking light case to the frame and that cured it. Sometime later, I realized that while I had low beams when I engaged the high beams, I had no headlights at all. I changed the dimmer switch and that wasn't it. What am I overlooking to cure this situation? I am pretty sure it is a ground problem somewhere and may be simple to fix.

Any help is appreciated.

twintracks

High beams use a different filament in the low beam bulb. It's possible that all of your high beams are burned out. Test each bulb directly to the battery.
Otherwise, try running a ground wire directly from the battery, and start chasing voltage loss with a test light or volt meter. Clean all of your contacts on the bulbs and add some dielectric grease to the terminals, too.

oldcutlass

Have you unplugged the lamps and checked for voltage?

p518

I checked with a test light at the high beam plug with the high beams engaged and did not get a light.

To be clear, when I engage the high beams with the dimmer switch ALL of the headlights go out not just the high beams. Under normal conditions (low beam only) the low beam head lights are fine.

I believe this just started after the 'glass bumper was installed.

joe_padavano

What you are overlooking is that unless you have too much money, you should do simple (and free) toubleshooting before spending a dime on parts that you don't need. You also need to spend a few minutes looking at the wiring diagram for your car. The first thing you'll see is that the low beams use the same ground wire for both the high and low filaments, so if the low beams work, but the low beam bulbs don't light on high beam, the ground wires to those bulbs are working.

The headlight switch is fed from the red main power wire off the horn relay terminal. This wire passes through the main firewall connector, but if that terminal were bad, nothing would work. The wire then is split in a splice, where one red wire runs to the headlight switch.

From the switch, a light blue wire goes to the dimmer, where two wires (one light green for high beam, one brown for low beam) run back through the firewall connector to the core support and to each of the headlights. There are also black ground wires from each socket to the core support.

That's all there is to it.

Disconnect the dimmer connector. With the headlight switch on, is there power on the light blue wire? If not, find and fix the break in this wire. If there is power, jumper from the light blue to the green wire. Do the high beams come on? If so, replace the dimmer. If not, reconnect the dimmer and move to the headlight connectors. With the test light connected to the battery negative terminal, check for power on the high and low beam wires in each connector (be sure to properly switch the dimmer). If there is no power, fimd the open in the green wire (which may be in the firewall connector). If there is power but the lights still do not work, check the grounds for each bulb. Also verify that the small ground wire from the negative battery terminal to the core support is in place. And of course, verify that the individual bulbs are good by jumpering them directly to the battery.

At some point, this will uncover the problem, as there is nothing else to test.

oldcutlass

Since the lamps are grounded through the core support, I don't believe you bumper is causing this issue. The inner lamps are hi beam only, the 2 outers are a combination hi and low beam. On the outers there are 3 terminals, 1 ground, 1 for low, and 1 for hi. The inners have just a power and ground terminal. See if you have voltage at the floor switch to the lamps.

p518

Thanks. BTW... there is no such thing as "too much money" and I do not have enough.

joe_padavano

And yet, people continually throw new parts at a problem before even troubleshooting what is wrong. You are by no means the first.

p518

I returned the new part to my favorite-local parts house for a full credit. They are good people.

kjr442

I have had this happen to me in the past, and it was just the dimmer switch.

joe_padavano

I'll say they are! I'm not aware of any auto parts store that will give a refund on electrical parts. I'd say they're a keeper.

joe_padavano

From the first post in this thread:

I'll admit that it's possible for a new part to also be bad, which is why I included jumpering past the dimmer switch in my post above, but it's not that likely.

MDchanic

It sure sounds like a bad dimmer switch, but I agree with Joe (and his painstaking description of the procedure) that a bit of troubleshooting will reveal the trouble.
If it's not the switch, then a bad high beam power wire is pretty much the only remaining option of any likelihood.

- Eric