No headlights make things interesting.

[Hilljack51]

Hey guys, having some issues with the headlights on my 68 GMC. I have lights in the rear (running, brake,and turn), but only the fender and bumper light on the front passenger side.

I checked the voltage on the marker light the drivers side and only measured 3v?
Checked for power on the headlights, and got nada! Have power coming from the fuse but nothing anywhere else on the front of the truck.

But the big question is what the heck are those big boxes mounted on the radiator support? I'm assuming they're some sort of distribution box for the headlights. Is there any way to test them? Or do ya'll think that's where my problem is coming from?

[chevyman91]

Not 100% sure but I believe it is a regulator for the alternator. Someone correct me if I'm wrong.

[swamp rat]

No, the big black box with the 4 wires is nothing to do with the headlights, that the regulator for an externally regulated alternator..

You really need to spend some time in the electrical thread there are schematics and posts about lighting, a FAQ thread ect..

http://67-72chevytrucks.com/vboard/f...splay.php?f=64

[Hilljack51]

Originally Posted by swamp rat

No, the big black box with the 4 wires is nothing to do with the headlights, that the regulator for an externally regulated alternator..

You really need to spend some time in the electrical thread there are schematics and posts about lighting, a FAQ thread ect..

http://67-72chevytrucks.com/vboard/f...splay.php?f=64

Alright, thanks guys. I'll start doing some studying.

[Ol Blue K20]

Try the dimmer switch. should have power going into it (with the switch on) and power coming out of one of the other wires on low and the other on high.

[68gmsee]

I had a similar weird light problems with my 68 and installing several ground straps solved mine. Old rusty grime bolts don't provide a good ground path on these old trucks.

After you check the wiring and the dimmer switch as mentioned, buy about four ground straps at the local auto parts and start by grounding the radiator support, the cab and the bed to the frame.

Then make sure you have the one from the rear of the engine to the cab and make sure you have a clean connection on the battery ground to the engine. Check all other ground cables to make sure they have a clean connection.

[Hilljack51]

Thanks, 68gmsee. That'a definitely something I'll do regardless. I haven't really messed with trucks quite this old in a longgg time. So I was barking up the wrong tree with the regulator. I'm gonna try to do some more trouble shooting tomorrow and let ya'll know what I find....as long as it doesn't snow again!

[chevyman91]

Ya like 68gmsee said ground all the body out and also clean all the ground up so you know you have good contact. I've always grounded from battery to engine then from batter to frame. And rand ground straps to the body

[swamp rat]

I think its in the FAQ section but you could run direct battery voltage to your headlights by incorporating relays, the relays use the existing light wiring to trigger the relays only, once triggered the relays allow direct battery voltage to the lights, the result is brighter lights then the stock system which sends the battery voltage thru the switch, and dimmer on the way to the bulbs.