Weird Headlight Problem

[DougC10]

Hello, everyone!

I have a 1986 C10 Silverado 1500.

When I purchased the truck, I knew the headlights needed work.

When turning on the headlight switch, the top driver's side lamp turns on, but not the passenger side. When hitting the dimmer switch on the column, the driver's side top lamp stayed on and the passenger side lower bulb turned on.

First troubleshooting step, I replaced the lamps in case of defect. At this time, when turning on the headlight switch, the driver's side top lamp turned on, but no other lamps. When hitting the dimmer switch on the column ALL FOUR lamps were off.

I assumed this meant either a bad ground or wire in the harness.

My next step was to clean the ground connections with a drill and wire brush, replace a damaged ground from the harness. I installed the heavy duty headlight harness from LMC truck.

After installation, the behavior returned to what I initially had (turning on the headlight switch, the top driver's side lamp turns on, but not the passenger side. When hitting the dimmer switch on the column, the driver's side top lamp stayed on and the passenger side lower bulb turned on).

This afternoon after work, I will replace the headlight switch but am not feeling confident. I think this will require pulling down the steering column to replace the dimmer switch.

Is there another possible solution that might not be as hard as that?

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[Ricko1966]

I seriously doubt it's either switch. And before I replaced one even if I suspected it I'd test it. Where I'd start is unplug all 4 headlights. With a multimeter check each headlight socket for ground.(in ohms mode ground 1 lead of your meter,touch the cavities in the headlIght socket with the other) each socket should have 1 socket that should make your meter read 0.00 ohms to 0.2 ohms. After that in volts mode again 1 lead grounded headlights on low position check your top 2 headlight sockets,should be 1 terminal in each reads close to battery voltage( check battery voltage with the meter) in high position check for 1 hot terminal at each socket. Post results. Just thought what I'd do before that. Park facing a wall,look at the wall while wiggling all the under hood wiring,watch for flickers on the wall.

 

[DougC10]

I seriously doubt it's either switch. And before I replaced one even if I suspected it I'd test it. Where I'd start is unplug all 4 headlights. With a multimeter check each headlight socket for ground.(in ohms mode ground 1 lead of your meter,touch the cavities in the headlIght socket with the other) each socket should have 1 socket that should make your meter read 0.00 ohms to 0.2 ohms. After that in volts mode again 1 lead grounded headlights on low position check your top 2 headlight sockets,should be 1 terminal in each reads close to battery voltage( check battery voltage with the meter) in high position check for 1 hot terminal at each socket. Post results. Just thought what I'd do before that. Park facing a wall,look at the wall while wiggling all the under hood wiring,watch for flickers on the wall.

Okay, here’s what I’m doing, per your instructions.:

Disconnect all four headlights but leave the battery connected (not a problem, since I am halfway through swapping out the headlight brackets and the grill is still off).

Set my meter to Ohms, Touch one lead to the ground point and check each of the sockets for a reading between 0 and 2.

After confirming that I have ground in each of the 4 sockets, switch to voltage mode and determine the current battery voltage.

Turn on the headlight switch and check the low beam sockets to see if one has battery voltage.

Next, engage the dimmer switch and check all 4 lamps to determine if I have voltage on a socket at each.

I’ll get to work on it in a few minutes and report my findings.

 

[Ricko1966]

0 and .2 check battery voltage at the battery 1st so you know what battery voltage is.

 

[DougC10]

0 and .2 check battery voltage at the battery 1st so you know what battery voltage is.

Battery voltage is 12.62 vdc

Passenger top lamp:

.3 Ohm
12.62vdc

Passenger bottom lamp:

.4 Ohm
12.60 vdc

Driver top lamp:

.4 Ohm
12.45 vdc

Driver bottom lamp:

.4 Ohm
12.45vdc

The readings may be off a little. I had to use my cheap meter because my Fluke is dead as a doorbell, tried two sets of new batteries on it.

 

[DougC10]

Also, a couple more points:

This occurred same pattern (no passenger high beam, no driver high beam) with the old headlights. I switched to LED and same results.

Today, I broke the ring off the ground wire from the harness and had to extend it, used the same gauge wire and this time grounded to the battery terminal. Got the same results as when grounded to the chassis.