2000 Blazer Headlights

[ajvp]

I'm at a loss.

Just got (2 weeks ago) a 2000 Blazer 4dr 4x4 for the wife. Everything seemed fine until she noticed a problem with the headlights... So here is what it does... The DRL turns on all 4 lights (hi and low). When you turn on the headlight switch, all 4 come on (with no highbeam indicator on inside.) When the lights are off and you flash the lights (with the multifunction switch) you get all 4 (and the highbeam indicator inside works.) Using the multifunction switch does nothing except when the lights are off. The Automatic lights turn on all 4. I noticed that a ground was replaced/installed on the pass. side connected to the lowbeam blue wire. (disconnecting this new gnd wire = no headlights at all) I thought maybe someone had installed some sort of Quad mod but I don't see any diodes b/t low & highbeams or anything else modified.

I've replaced:
headlight relay
DRL relay
headlight switch
multifunction (turn signal) switch

I have another headlight harness (incase I missed something in the headlight wiring) coming from s10Warehouse.

I kinda remember seeing somewhere, someone said that it might be a problem in the BCM. Does anyone buy that?

Anyone have any ideas (besides taking it to the dealer?)

I have posted this question on another forum so for those who have seen this b/f I appologize.

Thanks
AJ

[Mikz86TA]

Sounds like someone had aftermarket hi-watt lamps in there at one time and used a relay/grounding kit to add the required volts. The factory system uses a different than normal wiring since it had DRL and Auto Lamps. You might need to peel back tape and loom to find the orig wires and reconnect them properly. Is there any additionaly relays you can see? I believe Dk.Blue is the Ground on both low and high on the RIGHT side and Yellow-Black is on the LEFT side. Right Hi = Purple Right Low = Yellow Left Hi = Purple Left Low = Yellow It could be a Ground triggered setup. Ill have to study that part a little more. Hope this helps a little

[ajvp]

"aftermarket hi-watt lamps" Never even would have thought of that.

Been looking for a schematic. The only one that I've found is for a '98 and is shows the Dk Blues on the right side as being fused hots. But mine is setup like you've stated Dk Blues on the right side to ground (except no ground on the left side... I may try to trace/add that next.) I'll start looking closer at the wires. (Probably will wait for the new harness since it's on its way.) Then start in if that doesn't do the job. Nope, haven't seen any extra relays (looked pretty much everywhere.) Yea, from what I've read, it seems like these are Ground switched (which really threw me off at first.) Then I realized... ahh... that's why people have problems with their dome light coming on or th car dying when they hit the brakes (and allot more weird stuff.)

Just got the GM Blazer Service Tech Manual on DVD (off ebay.) Hopefully, it will have the schematics I've been searching for.

I'll give an update in a few days on my progress (or lack there of :D )

Thanks for you thoughts and time.
AJ

[Mikz86TA]

Hope you get it figured out. Some of the nice professional Hi-Watt Relay upgrade packs come in orig looking wiring. But the orig harness/plugs wouldve been there. What are the colors at the bulbs? Left Hi and Lo / Right Hi and Lo ? 1998-up is all the same

[ajvp]

Wires at bulbs as follows:
Lft Hi = Purple and Grn w/ wht
Lft Lo = Yellow and Yellow w/ Blk
Rt Hi = Purple and Blue
Rt lo = Yellow and Blue

Now if this is Ground switched (I'm betting you're right) then the one that looks like it's been added to the Blues on the Rt side shouldn't be there. (looks like they shaved the Blue wire and put a wire from it, to the body.)

I'm now thinking that this is part of the problem. According to the schematic (from the GM Tech DVD) it shows that the Blues should connect together then hit the 15A fuse then the relay (no mention of a Ground.) I'm trying to find the Ground, if there is one, but the grounds seem to be shown on a different Ground circuit schematic (there's allot of them and unlike the regular circuit schematics these are only labled with a # like G120 or G109.

Wish I could capture the screen but the program seems to be blocking Ctrl-C and PrintScreen.)

Basically the Headlight/DRL schematic says this: (just about what you described)
Lft Lo - Yellow w/ Blk - to the fuse then to the Headlight relay
Yellow - to the Multifunction SW.

Lft Hi - Grn w/ Wht - From the DRL relay
Purple - to the Multifunction SW.

Rt Lo - Blue - to the Blue on the Rt Hi then to the Headlight relay
Yellow - to the Multifunction SW.

Rt Hi - Blue - From the Blue on the Rt Lo then to the Headlight relay
Purple - to the Multifunction SW.

New harness should be here tomorrow (I'm hoping.)

Will keep you updated.

Thanks
AJ

[Mikz86TA]

Correct
Right High and Low have D.Blue wires that connect together and go to the 15amp fuse at the underhood fuse panel labeled RT HDLP
Left High and Low have Yellow-Black wires that alos connect together and go to the 15amp fuse at the underhood fuse panel labeled LT HDLP .
Right High ON is a grounded signal through the Purple wire
Right Low ON is a grounded signal through the Yellow wire
Left High ON is a grounded signal through the Purple wire
Left Low ON is a grounded signal through the Yellow wire
The only proper way to get the needed result to apply a Hi-Watt bulb to the truck is to wire in 4 seperate relays near the lamps.
Sounds like the previous owner didnt know what they were doing and tried to rig it. Or was trying to fix a problem with little knowledge of a BCM-type electrical system.
The rest of the headlight wiring in respect to the Multi-Function lever, DRL system, Auto Lamp system, Flash to Pass and the rest is a clusterfu*k of here to there and relays. Im not even going into that right now.
Remove that ground(s) added, test the wires induvidually with a voltmeter (digital preferrebly) (one that has a continuity check for the grounds) and check those two afformentioned fuses. Be safe and check all fuses inside and underhood.
Chack the grounding triggers with turning the lamps on and highs on too. Check for power from the Dk.Blues (RT) and Yellow-Black (LT)

[ajvp]

Update:

Yep, removed that extra ground. Result was no headlights at all (this includes the DRL and Autolamps.

Got the new harness... it did jack. Checked the voltage at the headlight relay (in the fuse box under the hood) and got the following:

30 - 12v constant
87 - Gnd
or vise-versa however you look at it
85 - 12v only when the headlight switch is on (or when you "Flash to Pass")
86 - Gnd
or vise-versa however you look at it

I believe this is working correctly.

I can hear (and feel) the HDLP relay switch when you go from Hi to Lo-beams but get no lights. So I checked the light sockets (without the bulbs.) Hitting the hots on each socket and a "body" ground I'm getting 12v, however using both sides of the sockets I'm only getting 8-9v. So I'm guessing that the reason that the lights aren't coming on is that they are only getting 8-9v. Since I checked everything under the hood, I'm guessing that whatever ground that is getting switched isn't a good ground? Or that there is something else under the dash that I'm missing.

Read on one of the forums that there might be another relay under the carpet on the driverside. But mine doesn't have such a thing. Nor did I see one on the schematic.

I'll check the color grounds you stated and see what I get.

Thanks
AJ

[Mikz86TA]

Headlamp relay is 30 = Battery 12V / 87a = Nothing (rested position when headlamp switch is OFF) / 87 = 12v present when headlamp switch is ON. This is the output From the 30 terminal 12v To the Lt and Rt 15a headlamp fuses. So, to tell if the relay is functioning, be sure the 15amp Left and Right headlamp fuses (RT HDLP and LT HDLP as marked underhood fusebox) are getting 12volts when headlamp switch is turned on. 85 and 86 are power and ground. Check for a constant presense there. Get back with those results.

[ajvp]

Here's what I found...

"Right High ON is a grounded signal through the Purple wire"
- Got 12V on Blue but no continuity b/t Purple and body ground

"Right Low ON is a grounded signal through the Yellow wire"
- Got 12V on both Yellow and Blue.

"Left High ON is a grounded signal through the Purple wire"
- Got 12V on Grn/Wht but no continuity b/t Purple and body ground. Also got 8.35V across Grn/Wht and Purple.

"Left Low ON is a grounded signal through the Yellow wire"
- Got 12V on Yellow/Blk but no continuity b/t Yellow and body ground. Also got 1.15V across Yel/Blk and Yellow.


"Check the grounding triggers with turning the lamps on and highs on too. Check for power from the Dk.Blues (RT) and Yellow-Black (LT)"
- Dk.Blues (RT) had 12V
- Yel/Blk (LT) had 12V
- Grn/Wht (LT) had 12V


Checked the relay. Just as you said. The fuses are getting 12V when the headlights are turned on. I can hear & feel the relay switch when I hit the "Flash to Pass" and when I turn on/off the Headlight Switch. As for 85 and 86...
with lights off:
85 - 0V
86 - 0V
with the headlight switch turned on:
85 - 0V
86 - 12V


I don't know if it's supposed to do this in some fashion but here is something else I noticed with the "Flash to pass." With the Headlight Switch off.
Pull the TurnSig lever once (and hold it)
(measuring across the sockets w/o bulbs)
Rt Lo - 9V
Rt Hi - 1.6V
Lt Lo - 1.65V
Lt Hi - 9V

Pull the TurnSig lever again (and hold it)
Rt Lo - 9V
Rt Hi - 1.6V
Lt Lo - 9V
Lt Hi - 9V

Pull the TurnSig lever again (and hold it) it goes back to the 1st set of numbers. It keeps alternating.

Keep in mind that I have no way of knowing if the Hi-beams are on or not. The inside Hi-beam indicator light is on all the time (except when you actually pull the TurnSig lever and then it only goes off when the lever is in the pulled back position. Once released the indicator light comes back on.)

Check all fuses & cleaned all the grounds I could find under the hood.

Thanks
AJ

[Mikz86TA]

In your info on the Right High, you said you have no continuity between Purple and Chassis? I doubt if you get any continuity since the Grounding Triggers are through relays. Right Low said you have 12V at both wires. Is that when Low beams are off? If so thats correct. Like a domelight, the trigger is a ground to turn it on. So both sides will have power (12V goes through the light and gets lit by the application of the ground. Its series wiring. Aslo I find it weird that on one side the wires are corresponding (Rights have Blue as 12V both Hi/Lo) and the other side doesnt (Lefts have Yell-Blk and Grn-Wht). That Green-White should be a corresponding Yellow-Black just like the other Left has. They are both ties together at the LT HDLP fuse. Trace that wire. Try to tap the Yell-Blk from the LeftLow to the LeftHigh temporary and disconnect the Green-White. Nex on to the relays. So 86 is your 12V trigger from the headlamp switch. Should be a White wire there if you are tracing stuff down. Continuity check will verify that. Lemme look at something else and Ill get back

[ajvp]

Broke down and took it to the dealer. According to them, it was the BCM. $400 for labor (to trace out the problem) and $350 for the BCM.

Thanks for all your time and help.

AJ.

[Slacker1357]

:hypnotize
I know wiring stuff... but all that schtuff just confused the **** outta me.
almost literally, I have to go....:D