Yes that's what I did with bulb out.ill check that fuse now

 

I checked that fuse and it's good.

 

A few things:

Measuring resistance on a powered circuit (yellow/black with power on) is of no value and reading is suspect. Thats why I only asked for resistance on the ground wire. In manual mode you have power to the yellow/black wire which is good and an open circuit on the yellow ground side (no continuity between the yellow wire and battery ground so the bulb cannot light and we need to figure out why the ground is missing. The reason why you see 12v on the yellow wire in this case is because the ground is missing and you see the passthrough voltage from another bulb. If this gets complicated then we may have to remove all the other bulbs and rule out a short to power, not the most likely reason for this.

On your second test you also have 12v on the yellow/black wire and continuity between the yellow wire and battery ground as it should be so the bulb should light. But you also have 12v on the yellow wire and those two things cannot coexist. Are you sure the bulb is OK? I will stick with you as long as you want and I will teach you anything you need but we have to get basic meter usage skills under our belts. I helped a lady last year find a headlamp problem that multiple mechanics could not fix and the dealership passed on and she never held a meter in her hand before but she followed my instructions exactly to learn the ropes and answered and confirmed back every step until she understood what we were doing..

1) So the low beams never work in any mode?

2) Do the high beams ever work?

3) Does the flash to high beam function work on the multifunction switch?

4) Did you replace the Daytime Running Lamp relay and are you sure that it was a known good relay?

Addressing your original question, can the MF switch be responsible for failed low beams - yes but not failed low beams in every mode because the MF switch is not always involved in presenting ground to the bulbs.


George

 

Also, this is a ZR2 correct because the circuit for this area is different.


George

 

The low beam never works
the high beam works and it will stay lit flashing function works as well.

I swapped the DRL relay from my s10 with working headlight. Didn't change anything.

I didn't know about the key needing to be off when checking resistance. I just checked both prongs with key off bulb out and got.450 resistance on both.

 

Yes it is a zr2

 

Normally you would only check circuit resistance on an unpowered circuit and that certainly applies to the powered yellow/black wire but a resistance check is not necessary because you are getting proper voltage. If there was no voltage on that wire then we would turn the truck off and disconnect some wires/connectors at both ends to start looking for continuity problems. Under most circumstances then we would check ground wires with or without power but power is actually needed in this case because the ground circuit passes through relays which are powered. Thats why I didnt say turn the power off i said that testing a powered wire for resistance does not work. The ground side is not directly powered by definition but the relays that control the ground routing are. Your cutting your teeth on less than a simple circuit young skywalker.

So what do we now know:

1. The actual ground on the engine block for the headlights and many other functions works
2. The MF switch works for HB and flash to HB. Could this switch have failed very selectively for the low beams only, maybe BUT:
3. One of the low beam modes does not pass through the MF switch so this cannot be the entire answer to this problem. Could there two failures at once, yes but not likely.
4. So we are left with wiring, connectors and the BCM because that module issues the control for the DRL relay which is involved in all of this. How easy is it to access that relay, I have never had to go looking for it? We may need to go looking for the BCM signal and power/grounds into and out of that relay.
5. Your sure the bulbs work?

George

 

I replaced one of the bulbs and nothing still neither look blown. The BCM doesn't look too hard to get to. There is a ground on the back passenger side of the block that's a little chewed up but I tried running the test light to the negative terminal to that ground and nothing happened.

 

Can you explain this further, you ran the test light between what two points?

As I said, how hard is it to get to that relay for testing?

George

 

I believe I've found the issue.

Same exact thing as this one.
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https://blazerforum.com/forum/2nd-ge...w-beams-41857/

#4 pin on mine is burnt as well