Head lights

['70GMCStep]

I wanted to run this past you all. I've got parking lamps and tail lights, but no headlights. I put in a new headlight harness and a new headlight switch. It appears to be all grounded right, but the lights don't turn on.

I thought I'd run it past you before I went and ordered a front harness. Kind of got me baffled, but I'm no electrician either. Thanks guys.

'70GMCStep

'65 Chevy C-10 lwb bbw
'70 GMC Stepside

[61_FL_Apache]

Check your connections at the firewall on the engine bay side. See if you have any voltage there.

[Clyde65]

I agree with 61, if you dont have power at the core support, follow the wires back to the firewall. If you dont get anything there, then I would check you headlight switch and how the wiring is done there.

[463]

check for power in and out of you good old dimmer switch. i'am thinking thats the weak point. heres a link on the wire dia http://6066gmcguy.org/headlight.htm

[1Bad62Pro/Street]

Checked Ground wire?


Wiring Diagrams:
http://www.google.com/custom?hl=en&s...iagram&spell=1

[61_FL_Apache]

Your issue is going to start at the headlight switch. Find the pin on the switch for the headlights. Trace that forward thru the firewall to the core support. There should be a plug on the driverside coresupport behind the headlights if I remember correctly.

['70GMCStep]

Thanks for the advice guys. I'll take this to the garage.

'70GMCStep


'65 Chevy C-10 lwb bbw
'70 GMC Stepside

[protrash64]

I've had the connector at the core support come loose after putting on a new grill. Check connections and grounding if everything else appears to be correct.

[Slow Build]

Originally Posted by 463

check for power in and out of you good old dimmer switch. i'am thinking thats the weak point.

That's where I found my problem.
Have you tried both high and low beams?

[markeb01]

It's helps if you also put dielectric grease on all the connectors like at the bulkhead and dimmer switch. It provides a better electrical connection and also keeps them from corroding/deteriorating.

['70GMCStep]

Yeah, I am not getting dim or bright on the headlights. The connection is good at the radiator support and the same result occurs with the new headlight switch and the old one that may have still been ok.

I picked up a voltage checker last night and dielectric grease I will need to pick up. I'll check all that and see where it goes. What I'm needing to do someday anyway is replace the underdash harness as it shows wear and tear. Thanks again for the advice. I'll post what turns up.

'70GMCStep

'65 Chevy C-10 lwb, bbw
'70 GMC Stepside

[Clyde65]

fuse?

['70GMCStep]

Hey as far as fuses go, which one do we need? There are many at parts stores that are the same sizes, I am assuming that a 32 volt or lower is fine? I've not done any upgrades yet (wiring is the only thing not new/rebuilt on my truck)

I picked up a set of these today. I might try to post a picture of my underdash harness and see what you all think.

'70GMCStep

[61_FL_Apache]

Originally Posted by '70GMCStep

Yeah, I am not getting dim or bright on the headlights. The connection is good at the radiator support and the same result occurs with the new headlight switch and the old one that may have still been ok.

Did you get any voltage at the core support connection?

['70GMCStep]

I'll go home and tinker some more. Using computer at work since mine is getting repairs. I'll see what I find.


'70GMCStep

'65 Chevy C-10 lwb, bbw
'70 GMC Stepside

[nachodog2]

I had a similiar problem on my truck and it ended up being the high beam switch was bad. Installed a new one and they worked.
Posted via Mobile Device

['70GMCStep]

Hey guys,
Finally got to my garage this week and I have voltage at the headlight switch, (all except the white wire which is the ground??) voltage at the horn, voltage reg., alternator, dimmer switch on the floor, and fuses.

Have no voltage at the firewall, and support where the front harness hooks up to the headlight harness, which is new.

Wiring bad somewhere on the front harness from firewall to radiator?

'70GMCStep


'65 Chevy C-10 lwb, bbw
'70 GMC Stepside swb

[Clyde65]

look at the connector on the FW, I had one of the blade connectors slide back away for the front harness connector back when my truck was original.

[protrash64]

Originally Posted by '70GMCStep

Hey guys,
Finally got to my garage this week and I have voltage at the headlight switch, (all except the white wire which is the ground??) voltage at the horn, voltage reg., alternator, dimmer switch on the floor, and fuses.

Have no voltage at the firewall, and support where the front harness hooks up to the headlight harness, which is new.

Wiring bad somewhere on the front harness from firewall to radiator?

'70GMCStep


'65 Chevy C-10 lwb, bbw
'70 GMC Stepside swb

If you pulled the engine side harness off the plug at the firewall, and tested the metal tabs on the firewall, the problem is in the dash portion of the harness.

['70GMCStep]

Sounds good. I'll give it another go. I'm checking this periodically at work since my home computer is at the doctor and won't be back until next week. I'll try it this weekend again and see what happens.

Thanks for the advice guys.

'70GMCStep

'65 Chevy C-10 lwb, bbw
'70 GMC Stepside swb

[fleetsidelarry]

headlights aren't fused on our trucks. white wire should be for the dome light according to the diagram.

when you said you had power at the dimmer switch, did you mean power out both sides (high and low, depending on position) as well as power into the switch? the out wires from the dimmer switch should run directly to the firewall plug. if the dimmer switch is working, the problem is porbably the firewall connector. I got so tired of mine giving problems I just by-passed it, running wires from the dimmer switch thru the firewall. I did this when I wired relays into the headlight curcuit to take the load off those wienie OEM wires.

here's another diagram that's a little easier to read:

http://67-72chevytrucks.com/vboard/s...d.php?t=324713

['70GMCStep]

Hey wait a minute.

This is a stupid question, but should the dimmer switch be showing power whether on bright or dim? I think that is what you are saying. I hope you are, because I have no power whatsoever on the dimmer when the switch is on "dim", just on "bright". If that's the case, maybe this is solved?

Thanks,

'70GMCStep

'65 Chevy C-10 lwb, bbw
'70 GMC Stepside swb

[fleetsidelarry]

when you pull the headlight switch on, it sends current to the dimmer switch, which routes it to either low or high, depending on the switch position. there's no "off" position. what sort of tester are you using?

['70GMCStep]

The cheap Harbor Freight kind that you ground and then the light comes on when there is voltage. Probably not the best even for an amateur though.

No voltage or lighting up when testing dimmer switch on "dim".

[fleetsidelarry]

Actually, a test light is perfect for this sort of problem. no need for anything more sophisticated, although, if you plan on working on these old trucks very much, you might want to invest in a better one.

if I understand,
1. you have power in to the dimmer (blue wire) and power out in one position to high beam (green wire) but no power out (to the tan wire) the next time you click the switch.

and,
2. even with power coming out in the high beam position (into the green wire), you have no headlights.

if #2 is true, then you still have a problem between the switch and the headlights.

to check the dimmer switch, pull the plug from the dimmer, make a short jumper wire, and bridge the connections (one at a time), blue to green and then blue to tan, and see if you have headlights in each of those configurations. if not, pull the firewall plug and see if power is getting to the connectors.

its a matter of tracing the current to the fail point and you may have to unwrap some wires to follow their path.