'77 wiring/headlight problem

[Sak]

I have a '77 I rebuilt from the frame up, and installed a brand new Painless wiring harness a couple of years ago. Literally everything electrical has been replaced with new equipment. I've only run the Bronco in town, and all the lights have been working fine up until now. While troubleshooting my dual tank switch (the sending unit was not working) I created a few lighting issues for myself. I had to back the instrument gauge out of the dash and I think that's when things went haywire for me. Not sure exactly what happened, but here are the stats:

Headlights: They light up on "low" beam, but not "high" beams (both headlights are new within the last 200 miles, as well as the high beam switch).

Turn Signals: All work front and back, although the RIGHT front turn signal is weak - it's not really obvious it is blinking.

Front side marker lights: All work with the exception of the RIGHT front, which I checked and the bulb was burned out.

Interior/gauge lights: All work

Hazard lights: All work

Thoughts on next steps to diagnose problem?

 

[DirtDonk]

I don't believe that there is a separate fuse for highs and lows involved here, but you might just check that anyway.

Are you running a headlight relay harness? If so, there might be separate fuses for each.
Also, a relay can stick or just fail completely. Easy way to check is to swap them one for the other and see if the trouble follows the relay.

Unfortunately, we can no longer assume that a switch is good just because it's new-ish and has worked before.
To that end, bypass the dimmer switch with a jumper and see if the high beams come on.

Not sure what you could have done up under the dash, but obviously that did something. One more reason to suspect the dimmer, as that's the only thing (other than the headlight switch itself) that is anywhere near there. If the power is getting to the low-beams, it's getting to the dimmer switch. Hence the bypass test.

A dim light is suspect regarding a bad ground or otherwise faulty circuit, socket, or bulb. See if you can fix the dim turn signal light as well. Do it first and you might just find your high-beam problem too.

Good luck. I'm sure the others will have some good tips for your search.

Paul

 

[DirtDonk]

Oh, and welcome to ClassicBroncos by the way too!

Paul

 

[gnpenning]

welcome..
Paul gave you some great starting places. does the high beam light come on the cluster? Are you using a test light or DVOM for testing?

 

[Sak]

Thanks DirtDonk and gnpenning. Appreciate the quick replies.

The "high" beam light does light up on the gauge cluster, and no, I have not used a test light. For now, I've just been simply testing "on/off" for all the lights.

Also, I don't believe the Painless wiring harness has a headlight relay built into it in its stock form, and I've not customized it. I am an amateur, and wanted to keep everything stock so it would be easier to backtrack any problems in this, my first build.

I will try the jumper, perhaps a new dimmer switch altogether, new bulbs, and re-grounding the RIGHT front lights. I've got to travel for work most of this week so may not be able to get to it, or respond till next weekend so please understand.

Thanks again for the advice.

Tom

 

[eric0o1]

dim right turn lamp, like DD said, would indicate a bad ground at the bulb. Does the right turn indicator stay lit when the turn signal is in the up/right position?

as for the high beams not working, you've verified the switch is switching power between high and low, by the high beam indicator coming on, but that doesn't mean the dimmer switch is switching enough voltage/amperage to illuminate the headlamp, just enough to turn the small incandescent bulb on. I would disconnect a headlight connector at the headlamp and see if you have power on the red/black wire; Red/black is the high beam wire. If you have power at the connector, you either have a bad connection to the lights or a bad light. The low beams working verifies the ground to be good.

If you do not have power at the connector I would replace the dimmer switch.

If you don't already own one, now would be a good time to purchase a digital voltmeter

 

[DirtDonk]

The free Harbor Freight one is a very good investment right now. ;D

Paul