Howdy folks, spent quite a bit of time searching the web and this forum for answers and haven't come up with anything definitive. Hopefully .......

2000 Blazer LS, 4x4, 4dr, 4.3 .... totally stock as far as I know and no reason to believe otherwise. Recently replaced CKP sensor and did the relearn, replaced auto trans TCC valve and PWM selonoid and cleared the codes, put the drivers side under dash panel back together (unknown why it was apart but found nothing out of the ordinary), replaced fuel filter and air filter, general under-hood cleanup.

While replacing various burned out bulbs discovered that the drivers side high beam is inop. All headlight bulbs are OEM style 05s and 06s and have been tested to function. HB indicator on dash works as it should. Traced wiring from drivers side to pass side and found no faults, checked all fuses found no faults, checked the relay in the under-hood fuse box and have power to both sides. I have checked the grounds on the core support and they look good. I removed and inspected the under hood fuse block / relay center and have checked wiring from bulb connectors back to the under-hood fuse block and have continuity on all related wiring and the fuses and relays are all good. Also inspected the interior fuse box and fuses and found no faults.

Recap of findings so far: (ALL TESTING DONE IN A DARKENED SHOP)
1. Key on - In Park = No headlights at all
Key on - In Gear - in sunlight = both High Beams on (presumably the DRLs)
Key on - In Gear - in darkened shop = both Low Beams on (presumably Auto Headlight system) (DRLs off)
Key on - Headlight switch on - multi function switch in LB position = both LB on
Key on - Headlight switch on - multi function switch in HB position = dash HB indicator on and only right HB on

2. Key off and removed = no lights
Key off - headlight switch on - multi function switch in LB position = both LB on
Key off - headlight switch on - multi function switch in HB position = dash HB indicator on and only right HB on

I removed the Drivers side under dash panels and found nothing unusual or out of place. No amount of fiddling around or wiggling wires and connectors down there had any affect.

I have not checked the "Body Block" under the dash yet. This Blazer doesn't have Fog lights.

Possibly related issue ...... the courtesy light override switch doesn't function as it should and will not remain in the override position. Additionally, the multi function switch occasionally will not switch from high to low. I have checked for continuity on HB grounds from drivers side to pass side and it's good. I have no power getting to the drivers side HB connector. However, I still have current to the LB connector when the HB are switched on (I presume that is the AHLs).

I have read that different models of these blazers used different wiring schemes and colors so if it makes any difference to those in the know ....

Drivers side HB wiring is Purple - and Green/Wht +
Passenger side HB wiring is Purple - and Blue +

Drivers side LB wiring is Yellow - and Yellow/Blk +
Passenger side LB wiring is Yellow - and Blue +

Hopefully someone can chime in and point me in the right direction .........Thanks in advance for any comments / help.

 

Hmm, was hoping one you Gurus out there would chime in.

Today in high hopes I replaced the dash headlight switch. While it did resolve the courtesy light bypass issue it did absolutely nothing for the inop high beam.

Next attempt was to remove the BCM from behind the ashtray and oen for inspection. No sign of corrosion or any other issues. At least I think it was the BCM. Three large connectors - Purple, Blue and Brown - interior was essentially a circuit board. Not what I expected .......... I thought the BCM was going to have several relays on board. I would appreciate some help on that as I am just about out of options here.

My last option based on research is to replace the multi-function switch. Guess I'll try that next time I can get in to the Pick n Pull.

Holding out for some help..................................

 

Anyone,

 

REVISED after further study:

Just a guess here.

DON'T Replace the (NOT blown) "LT HDLP" fuse in the fuse block under the hood.

Swap the DRL relay with some other relay for something less critical. If that fixes it, order a new relay. If this doesn't fix it, check the FOG LP fuse and replace it if it's blown or missing.

That's the most FUBAR headlight system wiring diagram I've ever seen.

The LT HDLP fuse powers both high and low beams on the left side. The power for the left high beam (only) goes through the DRL relay, and it looks like power for the left high beam only goes through that relay when the DRL's are off.

One more "one more thing:" You say you don't have fog lamps, but you will still need to have a good 15A fuse in the under hood fuse block in the "FOG LP" position. That fuse powers the DRL relay in addition to the fog lamps. Without it, the DRL relay won't work right (and that will kill only the left high beam with the lights on, but not for DRL's).