The Stovebolt Site Forums The Shop Area The Electrical Bay dim headlights

My headlights on low beam are quite weak. High beam is about what a low beam should be. My tail lights are okay. It is a 12 volt system with an alternator. I've checked the headlight grounds on the inner fender and they are clean and the paint has been removed to make a good ground. The truck is fully restored and all the wiring is new. I considered the ground strap from the motor to the chassis but if my tail lights are okay then it must be all right. Any ideas would be welcomed.

The first thing I would do is check what voltage I have coming from the headlight switch down to the dimmer. Then I would check the voltage going out the dimmer to the low and high beam lights and see if their is a large voltage drop. You could have a bad "high resistance" dimmer switch and it needs to be replaced. Next I would make up a jumper wire and connect one end of the jumper to the ground wire on the fender well going to the headlight and the other end of the jumper to the frame and see if the lights go brighter.....if so then you have a bad ground.

Try running a jumper wire directly from battery voltage to the headlight connections and see if it brightens up. If not, try going straight to the frame or the negative battery terminal with the ground. I second the motion to check the dimmer switch, they're bad about developing high-resistance connections.
Jerry

Thanks guys. I have run a jumper from the ground on the inner fender to the frame but nothing changes. I will try to bypass the dimmer switch with a jumper as well as your other suggestions. Will keep everyone updated.

After you figure out your problem, you might want to consider using relays to get a FULL 12 volts to your head lights, like I did on my 54 -- see Here

Sounds like the wires are misconnected on the headlights,ie,the ground is on the wrong headlight bulb terminal.To check, pull of the bulb connector and hold it with the business end facing you like an inverted U, one terminal on the top,one on each side.the left side is hi beam,top is low beam,right is ground.Then run a separate ground wire back to the battery negative for all lights on the truck,relying on the chassis for electrial continuity is a poor idea,car makers finally wised up on that 15 years ago.
And check the dimmer like mentioned above.

Pulled the headlights and checked the plug and they are set up right. I also emery-clothed the terminals on the light but no difference. I will now try to bypass the dimmer switch to see if it is causing too much resistence. Thanks

Hate to belabor this folks but here is what i've done. Checked the headlight socket wiring to make sure the right wires go to the right places. I cleaned the terminals. I've bypassed the dimmer switch and finally I ran a ground strap from the inner fender ground connection to a spot on the chassis. Still no difference. Thanks all.

Have you tried touching a jumper wire from the battery terminal say on the starter to the headlight wires going into the headlight on the fender well junction block to see if that changes the brightness?

Sounds like you need to do the following. Take a voltage reading of the electrical system with a meter at the battery and record that. Then take a reading at the wire coming from the headlight switch down to the dimmer and record that. Then take a reading on the high and low beam terminals on the dimmer and record those reading. If you don't see a big drop in voltage at the headlight switch or going through the dimmer then do the same test at the headlight with terminal at the back of the headlight to see if the drop is coming from the dimmer thru the junction block on the fender well and to the headlight plug. You might also want to try connecting the ground jumper from the frame to the ground wire coming from the headlight that is attached on the fender well.

I never had any luck connecting my headlight ground on the stock fender well location. I always brought my ground wire down to the frame.

I sure hope to hear you solved the dim light issue. Sometimes those gremlins just don't want to give up the battle very easy and will fight you to the end

Great tips Joe - thanks. I did run a jumper from the fender ground to the chassis ground strap. No luck. Fortunately I don't drive very much at night however having said that I'll be doing my first night cruise in tomorrow. It does stay light here until about nine thirty so I can get back all right I hope. I will follow your other steps on Sunday. One thing I should state is that all of the wiring is new. Thanks.

Just to be sure you're not overlooking something simple, try putting power and ground directly to the headlights with temporary wiring, and see if there's a difference in brightness. If so, there's still a gremlin in there somewhere you haven't found. It could be high-resistance contacts in the light switch! Doing a voltage drop check all the way through the system will isolate the problem, though.
Jerry

Ok, not for nothing, is the battery fully charged? Does the alternator put out around 14.5 volts with the engine running and lights on? Seems you have checked everything,are the headlight bulbs possibly defective?
If you're getting enough resistence to make the bulbs dim,a terminal or switch must be getting warm or even hot,use you hand to feel around.

Battery is fully charged and am getting about 14.5 volts. I had considered the sealed beams being weak but have not checked them. It would seem strange having both weak I thought. I will now try to run wires right from the battery to the lights and will let all know. Thanks again.

If the reflective surface of the sealed beam lights deteriorates, most of the light is lost out the back of the bulbs. I've seen this happen several times. Foe some reason, moisture can penetrate the lights, and cause the silvery coating of the reflector to degrade. Just for a check, try a new sealed beam, and see what happens.
Jerry

I run the halogen sealed beams and that makes a big difference in brightness. We are talking about brightness and not headlight alignment, right? The reason I ask is earlier you said the high beam is like what the low beam should be.

For Dennis M, no it is not an alignment problem but good call. I meant that the high beam brightness seemed the equivalent of a regular low beam. Also I do not think the bulbs are shot as the output bright-wise is the same. Anyway folks I am still trying and will let you know what happens. Many thanks again.

Sorry folks. I'vefollowed all the great tips but the lights are still dim. Dunno! Thankfully I very seldom drive at night. Thanks again. If this gremlin does finally disappear I'll let you all know.

oblu49 for the cost of one head light it might be worth just for the heck of it.

Don't know if this will help; it was made by a 'Bolter here (Chief).

AD lighting/ wiring diagram

I am on my way to buy a sealed beam. And I thank you for the beautifully done wiring scematic. Keep you posted.

Changed both sealed beams, no difference. I re-checked the battery output at the posts. Engine off about 13.5 volts. Engine running gives 13.85 volts and engine running with both high beam and low beam it drops to 13.60 volts. It is alternator equipped.

Hmm,13.8 is a little low but good enough for bright lights. Check the voltage at the headlight lamp,engine running at a fast idle,if it's about the same as at the battery, good.You said you ran a ground, did you run it all the way back to the battery negative? Never rely on the frame and sheet metal for grounding.Check the voltage again at the headlight terminal using the new grounding conductor. After doing that,if it doesn't improve,then there's nothing wrong,huh?

I agree with Truckedup ... check voltage at your headlights ... it's GOT to be lower there; I can't imagine what else could be going on.

If you're getting lower voltage at the lights, then relays will take care of that ... here's How

I did run my ground right back to the BATT neg terminal. Will try it all again. To check voltage at the lamps themselves to I just put a probe into the socket, or I guess I cound leave the lights attached and just run the probe onto the connection.
Alan I did look at your relay info and copied it, thank you. Will that information still apply to a 53 with a different wireing layout?
Thanks guys!

To get an accurate picture of the voltage drop, you need to check at each part of the circuit with the system operating. Even with bad connections, you'll see full battery voltage to the end of the circuit with no current flowing.
Jerry

olblu49 -- yes. The relays would wire up the same.

Ran another 14 ga jumper directly from the headlight ground wire to the battery negative post and the lights are still dim. Tried everything but am going to try to somehow by-pass the dimmer switch. Might be resistance there.

Just remove the wires from the dimmer, and clamp them together with a screw and nut. If the lights get brighter, replace the switch. There should be one hot lead coming from the light switch, and two leads leaving the dimmer, one for high beam, and anothet for low. WITH THE LIGHTS ON, check the voltage from each of the dimmer switch output leads to ground. I'll bet one, or boith of them is low-voltage. The circuit MUST be complete, and operating, before voltage-drop tests work.
Jerry

I was just working on my 50 Chevy pos,the lights have the same problem as yours,ain't that something.Not a grounding problem.I jumped the dimmer, no change,ran a 12 gauge jumper directly from the battery to the lights, still dim.Disconnect one headlight, the other gets bright, hook the wire back up,gets dim again.Reversed the procedure with the other headligh, same results.So for kicks I swapped the hi and low beam wires on one headlight,now both are normal brightness on hi and low beam.
I still question the terminations on your headlight bulbs. If you have a spare lamp, put a rag on it, smash the front with a hammer.Look to see with terminal is the ground,it'll be common to both filiments.Despite what may be supposedly correct, mine had the wrong hook up.

Thanks again guys. Hot Rod Lincoln just confirm how I check the dimmer switch. When I take the wires off I should run the lead from the switch to one output wire at a time - correct? Don't think that screwing them all three together would work or am I wrong? Thanks