The Stovebolt Site Forums The Shop Area The Electrical Bay “Winking Headlights”

My ‘47 AD Chev 1/2 tons lights have been puzzling. Alternating from high to low beam, they “wink” . Actually when I turn them on, one light is bright, the other is quite dim. When I hit the dimmer switch, the opposite light gets bright and the other goes dim. Ive addresses ( I think) all of the grounds. I’ve traced wires and spliced a 12 ga. Wire section to a POs splice thinking there was a flow problem.
Battery checks out, headlight switch turns on/off the parking/headlights. The dimmer switch alternates the hi/low beams but not to each headlight simultaneously.
I’m studying the wiring diagram now as the PO did some retiring. Every light works, but it’s the headlights that stump me.
There obviously I’m missing. I just want to throw all new switches at it if I don’t have to but I will if warranted.
Does anyone have suggestions that can lead me down the path to two headlights that are of equal brightness?

Check the ground wires to both headlights- - - - -one is open-circuited or has high resistance.
Jerry

Do the lights vary in intensity or just one on high beam and the other on low? If it's just one on high & one on low, swapping when you press the dimmer, I'd suspect the wires are crossed. I did that very thing as a young body man many years ago and got the embarrassing job of rectifying my mistake.

Check your grounds and make sure the buckets are grounded too.

Three great suggestions.,
Just to be more clear in my description with no grammatical errors!.........
When I turn on the headlights, one side is appreciably brighter than the other headlight. However it is much dimmer than “low beam” brightness. In fact, it’s “dim”. When I depress the dimmer switch, the bright side goes “dim” and the “dim” side becomes bright. I guess if I could pump the dimmer switch fast enough, I’d have continual bright lights! Haha
Tomorrow, I’ll recheck the ground screw/wire to each splash shield AND clean the male/female contacts of the headlight and the socket. I’ll also recheck the splice contacts done by the PO.
The screws holding the headlight bucket to the fender aren’t part of the ground system are they? Doesn’t appear they are to me.
I will have to check the wiring again......comparing it to the wiring diagram. One of my thoughts, too, was that the wires were crossed.
Back to the drawing board...Thanks for the suggestions.

Running the headlight ground wires back to the engine or frame makes more sense than relying on the splash shield to provide the ground, or at least add a ground wire from the splash shield to the frame on both sides. No telling how mush rust that current is trying to bridge on its way back to the battery. I'm also a fan of using relays to carry the headlight current and letting the dimmer switch trigger the relays only.
Jerry

If they are alternating like you said, it sounds like cross wires. I am confused at how it might be a ground if both headlights have high and low (dim) beams. If they have both, yet opposite times (one dim and one high) each time you hit the switch, wouldn’t one light have to be wired backwards?

I am not a smart man, but I accidentally did this when I rewired my truck.

Chris

If I am wrong, please explain so I have a better understanding.

One bad ground will make that headlight try to find a ground by backing up through one of the filaments of the other light. The added resistance causes a very dim glow instead of normal brightness. it also messes with the current flow when the dimmer switch is operated. That's also the reason brake lights, turn signals, and tail lights do oddball things when one bulb socket isn't grounded properly.

To test my theory, try disconnecting the headlight ground to one side on purpose and watch what happens.
Jerry

So what you are saying (in my inexperienced mind) is that if the ground is bad, it can cause one light to be bright and one dim because the affected side will back up and find a different electrical route (ground).

Jim,

Did you ever seen the lights working correctly? You stated that some of the truck was retired, are the lights included with it? Just a thought, Have you put a meter on the wires yet to ensure that the previous owner had it correctly wired or flipped the wires and retested?

Ground or flipped wires is a cheap/easy fix. I am curious as to what the diagnosis is.

Chris

Yes, that's exactly right. Since the high and low beams share a common ground, if that ground isn't there, the voltage will back up through the other filament, go to the opposite light, and seek a ground there. That puts two filaments in series, and dramatically reduces the brightness. In the case of rear lights with one bad ground, both tail lights will appear to be close to normal brightness, but one will go out when the brakes are applied.
Jerry

Bad grounds will make lights do some strange things, especially on a six volt system.

If your truck had eyebrows,,,,,,,,then I would worry about it winking at you.

Here’s the latest from the “winking lights”.
I upgraded my battery cables to the frame and starter with 1/0 cable. Couldn’t locate 0/0.
Then I cleaned grounds. Tried to resolve the problem as per the above suggestions.
Jerry, following your suggestion, did disconnect one sides ground. Darn other headlight was brighter than the sun off my large forehead! Now I must figure out how to clean/establish a better ground the the dim headlight.
However I’ve opened another can of worms......seems now, according to the indicator light on the speedo, I have NO headlights on low beams. When I ran a test light on hi beam it’s barely lit. Same light on lo beam is brighter. Could that reflect then the original light switch is a factor in this also? I’ll Check with the meter in a bit.
Back to the ole drawing board!
Like the mechanic set, “ it’s not acting up now, bring it in the next time it happens........”. Haha

It's possible somebody in the past has mixed up the wiring where the wrong prong of the 3-pin headlight connector is attached to ground on at least one side. When you're looking at the connector plug on the back side of the headlight, the center pin is NOT the ground. I don't remember offhand which one of the side connectors is, but it's pretty easy to figure out.
Jerry

Jerry,
I think that’s likely what happened. I was looking at the ‘47 manual & its wiring diagram and it looks as if the middle connector IS the ground. Anyhow I switched two connections and things worked out.....AFTER I shot some Radio Shack Electronics Cleaner into the original light switch. I knew the rheostat was bad as the dash lights needed massaging before they would light. I sprayed a “liberal amount” into the switch. Then I vigorously opened and closed the switch, meanwhile activating the rheostat.
The result......LIGHTS! So looks as the light switch should be replaced soon. Both the hi and low are lit. One low beam isn’t as bright but I can chase down that easily with a meter.
Thank you and everyone who took time to offer solutions!
The ole girl ain’t “winking” no more! :-)

Another potential problem with dim or inoperative headlights is the dimmer switch. It's down there in a very wet, dirty, salty, and generally hostile environment. I like to use the headlight switch and dimmer to carry very low amperage to switch relays on and off for the main headlight current. That setup makes regular lights noticeably brighter, and it's just about a necessity when an upgrade to halogen or high output LED headlights is done.
Jerry

A follow up to this dilemma:
As stated, I initially made 2 battery cables of 1/0 cable. I made sure I ground the frame to bare metal and even used a star washer as overkill. Then I waterproofed the outside of the connection.
Then I used a meter and traced all wires. Following all suggestions, I determined that two wires were switched by the PO. Once I made the switch, PRESTO! Yep, bright lights.
Then I went and cleaned all wire connections on the splash shield terminals. I did find one loose clip. The wire literally was pulled from the split clip. I replaced the clip.
Went to the fuse box and removed the wire connections and thoroughly cleaned all connections.
BEWARE....if you have original wires as I, the wires covers were very brittle. Had to do some repairing. A new harness is on the agenda.
Finally I decided to eliminate two other potential problems. Ordered a new light and dimmer switch.
Again, thank to everyone for. Your help!

Thanks for the follow-up report.

We should remember your post, and link to it, when future members talk about poor starting and weak "winking" lights.

Congratulations.