The Stovebolt Site Forums The Shop Area The Electrical Bay headlight Questions I'm stumped!

Ok here is the picture, a 1960 GMC with dual headlights. 1st what are the normal headlights that work on low beam? Outside set or the inside Set. "I" think the outside set are low beam.

At normal night time driving the low beam seems fine, when I hit the highbeam switch the truck headlights change angle and get brighter, but the same two lights are what is switching. (I swear I'm not making this up). The inside pair never come on. I did not notice this until last night when I pulled up to the garage and switched the high beam off.

I wonder how the PO has this wired or are is it simply the wrong bulbs on the truck?

I may be wrong, but I think that on high beam, all 4 are supposed to light up. I know that there's different #s for the bulbs, as I recall the 2 for the outer are dual intensity and the inners are single. Perhaps either there's a wireing issue (inners not hooked up, maybe) or the inner bulbs are shot.

sounds like your high beams are burned out or you have a problem at the dimmer switch. other than part # the bulbs have different plugs, 2 prong for low and 3 prong for high. sounds like 2 of your high beams are burned out.

all 4 should be on on High Beam, check grounds & bulbs & dimmer switch. I like to add grounds on this old stuff.

The outers are High/Low & the inners are High only in the stock configuration. It's difficult to say what the problem specifically. It's time to break out the multi-meter & start checking what has power when.

yep.

The inner ones don't come on at all. The wiring hardness is brand new factory OEM from the Truck and Car shop. I'll see if I can change out the dimmer switch, where would one begin to trace down a problem. I'm swapping cabs and will re-wire everything this winter, I will wait to do major re-wire, but you'd think this is an easy problem to solve ;(

Since the dimmer switch is operating, why would you change it? It switches the outer lights from high to low, so it is OK. Use a multimeter to diagnose your problem, don't just throw parts at it.

Put your lights on high beam then use your multi-meter to see if you have power to the bulb's plug. If you do you probably have bad bulbs. If not you need to find out why.

A test light is also handy for diagnosing lectrical, just poke it into the connector on the rear of the high beam headlight.

fleetside has the right idea on this one I think. You don't need a multi-meter to check a headlight circuit. Go to any FLAPS and get an inexpensive test light. Connect the clip to a good ground, turn the lights on high beam, and poke the probe into the socket. If the test light lights up, the problem is either a burned out bulb or a bad ground. If it doesn't light, start looking at the wiring, the high-beam switch seems to me is working like it's supposed to. Good luck!!

Yer right about being able to use a test light for this but with multi-meters selling for what a test light sells for & a multi-meter giving so much more info I automatically default to using my multi-meter.

My prediction, based on my recent tail light headaches: the left and right are not wired the same "up and down." I had illogically working tail lights (with dual filaments) and learned that I had one of the sockets turned 180° relative to the other one. This fouled up the brake/tail light operation so that I didn't have logical brights and dims.

Using a 12v power source, I learned which contact connected to which filament. Using a test light I learned which prong was for the bright and which was for the dim. One twisted socket later and I was back in business.

Bill

The thing I like about a test light is it works by sight, such as if I gotta step on the brake pedal to check for lights or hook something up temporary, I can see it light up from a distance or have my shop helper tell me, whereas it is hard to see a needle moving or a digital display from a few feet away & lotsa numbers confuse the shop helper .