My headlights seem to be going crazy. All bulbs test ok with a DMM. When doing a continuity test on the switch I think I found the fault. I have a 68 Cutlass, quad light setup, 2 low, 2 high. I am loosing power to the low beam when I switch to high. The dimmer has three prongs. Should I have continuity throught to both the outputs when high beams are on? I only get a complete circuit on on pin at a time. Any ideas?

Adam

 

I not a great electriction or speller. My guess is the floor dimmer is shot. After 40+ years of being stomped on you are bound to wear out. I had to replace mine found at Autozone for about $12. Took about 10-15 mins to change.
Larry

 

This is correct. You either get a blue to tan for low or a blue to green for high.
If they dim erratically or flicker (not flash) when the dimmer switched is disturbed, then the dimmer switch could be bad.

Keep in mind that the outer bulbs have both a low and a high beam inside (3 prong). Only one is on at a time.
The inner ones only have high beam (2 prong) so they are only on when highs are on.
Make sure you have the right bulbs in there or you will appear to lose the lows when the highs are switched on. A previous owner or maybe even a newer 'mechanics' did not know the difference.

Also make sure the grounds from the sockets are clean and tight and the grounds from the body and radiator support to the battery/block are secure.

 

Sooo. Just the high beam circuit runs in high beam mode. It powers both the high beam and the second terminal on the low beam bulb. I thought the HB and LB may have ran together. This is one of those "it all worked fine before it was taken apart," which was April '10.

Adam.

 

This is exactly right. This is the kind of problem that you should not spend more time on than the time it takes to run to the store, buy a new switch, disconnect and unscrew the old one, and then screw in and connect the new one. All power for the headlights goes through the dimmer switch. If there's any kind of problem like the kind you mention, the chances are better than 99.9% that it's the switch, and, given how cheap they are, it's easiest to just swap in a new one and be done with it.

 

The high beam switch is SPDT (Single Pole Double Throw), which means it's either / or.
It connects to the high beam output or the low beam output, but not both (and not neither).

Keep lookin'. Check all connections and grounds. Observe whether the problem affects ALL lights at once or not - it it's all of them, then it's got to be at a point where there's only one wire for them, such as the dimmer switch or headlight switch connections.

Look at the diagram in the manual and just trace it back until you find a choke point that would replicate your particular problem.

Headlight switches are about $12 as well, in case that turns out to be the problem.

- Eric

 

I will troubleshoot some more and let you know. Thanks

 

Here's the update. I had the high beam circuit pin push through on the low beam lamp. This caused the low beam on the driver's side go out when high beams are turned on. On the passenger side the low beam circuit of the lamp itself had an extremely high resistance compared to the driver's. When HB were on there was too much voltage drop across the whole circuit to light the defective low beam. At the LB position, lighting only two lamps, they would work. With all four lamps engaged that high resistance would not let the lamp light. A repaired socket and one new lamp and all is fine. Funny two problems on the same circuit, different lamps.

Adam

 

I have run across multiple issues on the same problem before on different things. Glad you looked at all that first and got yourself a no-cost repair!

 

Almost cost free. It did cost me a headlamp. I am really gald it was solved easily. I really hate electrical issuses.

Adam

 

Me too, but my career is based on them... If there weren't any electrical issues, i would not have a job...