1987 3+3 lighting issue

[Tom corsi]

What's up guys new to the forum.
So I just picked up a 87 c30 it's pretty rough I've had a couple 87s but this one has me stumped and I can't find anything online I'm pretty good with these old trucks but here is my issue the running lights and dash lights only work when you click the high beams on I haven't dug into it terribly far yet everything acts like Normal dimmer all that just only with the high beams on any help would be highly appreciated thank you

 

[Charlie]

 

[chengny]

What's up guys new to the forum.
So I just picked up a 87 c30 it's pretty rough I've had a couple 87s but this one has me stumped and I can't find anything online I'm pretty good with these old trucks but here is my issue the running lights and dash lights only work when you click the high beams on I haven't dug into it terribly far yet everything acts like Normal dimmer all that just only with the high beams on any help would be highly appreciated thank you

Need some details. Sorry, don't mean to get get preachy, but without punctuation it is difficult to understand your question. It's all one run-on sentence.

Anyway:

1. Quad or dual headlamp style?

2. What lamps work/don't work if the H/L switch is in the parking light position?

3. " " if the dimmer switch is in the Low Beam position?

4. Ditto with the dimmer in High Beam position?

5. Does headlight operation seem to be normal - in both high and low beam

6. When you say "running lights' do you mean parking lights (incl. side markers & plate lighting)

7. Have you checked your forward lighting system grounds

Without knowing much about your particular situation, it's hard to say. But it seems as if; switching to high beams isn't what makes all your lights suddenly begin to work. Rather, it is switching away from low beams that makes that happen.

This is a shot in the dark, but what if there was a short to ground in the low beam circuit? With the low beam feed leaking to ground, that would tend to cause a low current flow through the smaller lamps in the circuit (i.e the marker and plate lighting).

 

[Tom corsi]

I'm sorry. Yes it is the quad set up. If I pull the h/l switch to the parking light position nothing happens. Only the low beam lights come on. When I switch the blinker switch to put the high beams on all the marker lights and dash lights work. While I have the high beams on and push the h/l switch to the parking light position all the lights go off. Everything looks to be I. Place as far as I can tell.

 

[Tom corsi]

Oh and all 4 head lights stay on when i flip the high beams on with the h/l switch in parking position nothing works. When I pull it to the last position only the low beams work.