Head lights dimming while running

[rhc10]

Not sure how or where to trouble shot. Problem I'm having is that my head lights dim while the motor is running when stopped. When I accelerate they brighten back up to normal. Not really seeing this same issue with the dash lights.
Any tips on what this is or where to start checking?
Thanks.

[Andy4639]

Most likely it's a alternator problem are voltage regulator if your running the factory regulator. Hard to say not knowing which system you are running. Post back what system you are running.

[rhc10]

Originally Posted by Andy4639

Most likely it's a alternator problem are voltage regulator if your running the factory regulator. Hard to say not knowing which system you are running. Post back what system you are running.

I'm running a one wire alternator which I belive would have an internal regulator, right. The alternator is about a year old and its a high out put I think 200 amps. Is there a way of testing this?

[michael bustamante]

have you had the problem since converting to one wire or did it just start?

[gmachinz]

I'd convert to a 3-wire CS alternator and look into one of my headlight upgrade kits!

[rhc10]

Truck has always had one wire since I've owned it. To be honest I'm think it's always kind of done it but recently I converted the head lights from a sealed beam to a H4 set up which is brighter so I'm noticing it more.

[65 C20]

Do a search under headlight upgrades.
I forget how it is done, but if you put in some relays it will draw power straight from the battery not putting a big load on your headlight switch.
Not sure of your year but was mentioned in the 60-66 forum.

[gmachinz]

Your existing 1-wire may be up to the task but to me it appears you are experiencing excessive resistance in the headlight circuit. The reason for this generally is because your H4s are capable of putting out more light and in doing so they're trying to pull more amperage. The problem is when you try doing this through stock sized wiring (problem #1) and also through the factory headlight switch (problem#2). The switch has a built in ballast to restrict the voltage going out to the lights. Installing higher wattage bulbs only serve to make the situation worse since the ballast now has to block even more amperage-now you have a serious electrical hazard. If the ballast gets too hot, best case scenario it cracks and shorts out-no lights. Worst case scenario it melts the housing and starts a fire-no lights.....and maybe no more truck.
Before ditching the alternator (and assuming it has been correctly converted) try running the headlights off relay power and upgrade the headlight wiring too-you should see a big difference. In my harness kits I see about a 1.5V increase in voltage which loosely equates to approx. 20% more light output.

[rhc10]

Originally Posted by gmachinz

Your existing 1-wire may be up to the task but to me it appears you are experiencing excessive resistance in the headlight circuit. The reason for this generally is because your H4s are capable of putting out more light and in doing so they're trying to pull more amperage. The problem is when you try doing this through stock sized wiring (problem #1) and also through the factory headlight switch (problem#2). The switch has a built in ballast to restrict the voltage going out to the lights. Installing higher wattage bulbs only serve to make the situation worse since the ballast now has to block even more amperage-now you have a serious electrical hazard. If the ballast gets too hot, best case scenario it cracks and shorts out-no lights. Worst case scenario it melts the housing and starts a fire-no lights.....and maybe no more truck.
Before ditching the alternator (and assuming it has been correctly converted) try running the headlights off relay power and upgrade the headlight wiring too-you should see a big difference. In my harness kits I see about a 1.5V increase in voltage which loosely equates to approx. 20% more light output.

Thank you, where can I get more info on you harnesses and relays?

[gmachinz]

I'll send ya a PM on what I can offer for HO replacement front lighting harnesses-these are far more robust than even aftermarket offerings.

[earl84]

The headlight relay upgrade is a good one, makes a big difference. It can be done without a kit, but the kit might make it easier. I did my own wiring, but I had more time than money.
Could be totally unrelated, but I had a headlight that out of the blue started going dim. I have installed a new AW wiring harness, and was not too happy to see this after all that work. Turns out the plug was coming loose from the bulb, so it had a poor connection. Plugged it back in, no more dim lights. I need to figure out a way of retaining that on better. With the stock lights it was no problem, but the H4 lights have a little rubber cover, so the connector doesn't slide on as well. Hmmmm....

[Andy4639]

To check the alternator crank the truck up and at idle put a volt meter on the battery and see what reading you get.
Then rev the motor up to 2000 RPM's and see what you have.

At idle I would want 12.5 to 13 volts min.

At 2000 you should have 14.5 -16 volts. If you don't see these numbers then I would look at the alternator but I will say now after your last post it's the system itself. The relays are the best upgrade you can do to these trucks for night driving. If you have upgraded bulbs then you really need the relays.