New guy here. Wreched a bit and glad to have been accepted.

[calmtspot]

'85 C20 w/QUAD headlights. On highbeam, the old and new headlight switch has/will set internal breaker?, after 10 or so mins. All headlights will go out. Switch to low beams and the low beams will work. After a bit(switch cools) wash, rinse, repeat. 10.1.0 (yellow) at headlight switch to dimmer gets hot in high beam setting. Checked ALL grounds at core support and frame. Bus bar inside as well and ALL are grounded. Is the halogens just to much for the circuit? I believe a relayed circuit added to just high beams will work but want to correct properly if possible. Anyone else experienced this?Again, thanks for the add!

 

[Ricko1966]

'85 C20 w/QUAD headlights. On highbeam, the old and new headlight switch has/will set internal breaker?, after 10 or so mins. All headlights will go out. Switch to low beams and the low beams will work. After a bit(switch cools) wash, rinse, repeat. 10.1.0 (yellow) at headlight switch to dimmer gets hot in high beam setting. Checked ALL grounds at core support and frame. Bus bar inside as well and ALL are grounded. Is the halogens just to much for the circuit? I believe a relayed circuit added to just high beams will work but want to correct properly if possible. Anyone else experienced this?Again, thanks for the add!

Back probe each headlight ground at the headlight. Headlights on,meter set on volts 1 lead back probe headlight ground other lead on battery negative. Are you reading more than 1/4 volt on the meter? If so you have a ground problem,may not be the only problem but a problem. Do the same thing on the headlight positives and use battery positive post,again same thing are you reading more than 1/4 volt if you are you have a power problem also. Check headlight positive to battery negative,you should read real close to battery voltage,check battery voltage with meter compare readings. Post back

 

[calmtspot]

My suspicion is junction block connection. It possibly could be just because of age. When purchased, it had a dented L/F quarter panel. Loom is old but harness showed no signs of damage or repair. I understand your theory of possible resistance. Electrical is not my forte but not weak at it. Thanks and I will reply.

 

[ali_c20]

Welcome from Austria. I upgrade all my headlights with relay harnesses to remove the load from the switch and old wires.
You can buy them ready or the components and diy.

https://www.lmctruck.com/electrical/wiring-components/gm-heavy-duty-headlight-harness

https://www.summitracing.com/parts/prf-30814

 

[legopnuematic]

Welcome from Missouri.

 

[Mr Clean]

 

[Jgonick]

My suspicion is junction block connection

If I remember correctly, 1985 a red wire that feeds head light comes off the starter and goes directly to light switch. Doesn’t connect to junction.

Wiring diagram LINK
Here is a link to the wiring diagrams

 

[animal]

 

[JamesSam]

Welcome from VA.

 

[calmtspot]

Back probe each headlight ground at the headlight. Headlights on,meter set on volts 1 lead back probe headlight ground other lead on battery negative. Are you reading more than 1/4 volt on the meter? If so you have a ground problem,may not be the only problem but a problem. Do the same thing on the headlight positives and use battery positive post,again same thing are you reading more than 1/4 volt if you are you have a power problem also. Check headlight positive to battery negative,you should read real close to battery voltage,check battery voltage with meter compare readings. Post back

On driver's side Negative side battery to negative light connection 2 prong 0.86 volts. Passenger side headlight 3 prong to positive side battery to positive side connection 2.43 volts.

 

[Ricko1966]

On driver's side Negative side battery to negative light connection 2 prong 0.86 volts. Passenger side headlight 3 prong to positive side battery to positive side connection 2.43 volts.

Okay you've got a serious voltage drop on the positive side,when voltage goes down amperage goes up. You need to find where you are dropping voltage. Same test but probe hot lead in at switch and headlight positive.we need to keep moving our points where we test until we find where the drop is. Better yet same test but hot in at the switch and hot out at the switch,headlights still on.

 

[calmtspot]

Okay you've got a serious voltage drop on the positive side,when voltage goes down amperage goes up. You need to find where you are dropping voltage. Same test but probe hot lead in at switch and headlight positive.we need to keep moving our points where we test until we find where the drop is. Better yet same test but hot in at the switch and hot out at the switch,headlights still on.

Refresh my memory, but what is the convenience center on a 85 SB?

 

[Snoots]

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