# western ultramount on 2000 GMC NBS headlight question



## obrut (Oct 30, 2002)

I just recently installed a 05 western ultramount with the 4 port isolation module on my 2000 NBS GMC truck. I have a question about how the head lights and plow lights are supposed to work.

When the plow is not connected my head lights and bright lights work fine and the sensor automatically turns the head lights on when it gets dark.

If I connect the plow when the head lights are automatically on the plow lights are off until I flip the bright light switch in the truck. Is this right?

If I connect the plow when just the DRLs are on the plow lights are on but are very dim. 

I'm not sure if this is right can some when tell me how they are supposed to operate?


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## obrut (Oct 30, 2002)

BTW this came off of a 05 chevy, is there a difference in the harness?


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## obrut (Oct 30, 2002)

I just did the quick match on westerns website and it shows that there are two different part numbers for the headlamp harness. 27780 which is what came with the plow and 8437-1 which is what I need for my truck year. Which harness is this, is it the one that plugs into port #2 or is it #3 and #4? What is the difference with these harnesses?


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## B&B (Nov 4, 2006)

Yes, the light harness will be different between an '05 and your 2000 due to the lighting configuration change on the '03-up GM trucks. Your 2000 uses a negative to excite head light system and the '03-up's use the conventional positive to excite system, just like all the GM's did '98 and prior.. your light harness's plug into the number 3 and 4 ports on the iso module..


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## dlcs (Sep 2, 2004)

My '99 Silverado and my 2002 Silverado both used the harness with the relays and not the isolation module. Your headlights on your plow should operate just like the headlights on the truck. All you have to do is connect the plug to switch to the plow lights.


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## B&B (Nov 4, 2006)

dlcs;426103 said:


> My '99 Silverado and my 2002 Silverado both used the harness with the relays and not the isolation module. Your headlights on your plow should operate just like the headlights on the truck. All you have to do is connect the plug to switch to the plow lights.


 On a relay setup yes. But it's not that simple with a 4 port Iso setup.. the plow lights are positive to excite and the truck lights are negative to excite as one is '02 and older (neg to excite), and the setup came off an '03 and newer (pos to excite)


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## obrut (Oct 30, 2002)

yep there is a difference, however the isolation module is the same which tells me the wiring or pin out for the connectors is different. This shouldn't be too hard to change, I just need to know what the inputs and outputs for port 3 and 4 are and then switch my pins in my connectors. This can also be done by making an adapter to cross the wires over before going into the module but moving the pins around will have the same results.


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## B&B (Nov 4, 2006)

obrut;426201 said:


> yep there is a difference, however the isolation module is the same which tells me the wiring or pin out for the connectors is different. This shouldn't be too hard to change, I just need to know what the inputs and outputs for port 3 and 4 are and then switch my pins in my connectors. This can also be done by making an adapter to cross the wires over before going into the module but moving the pins around will have the same results.


 True that the iso is the same and you can move pins around..it's just that most guys either don't have the knowledge to do the pin move or aren't comfortable with doing it themselves and would much rather have it "plug and play" so to speak..


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## obrut (Oct 30, 2002)

I agree most would rather just have plug and play. I'm comfortable with moving pins around, but I also have experience making harnesses and reading schematics.


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## B&B (Nov 4, 2006)

Do you want the pin out diagram for the Iso module obrut? If so, shoot me a pm with your email address and I'll get it to you...


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## santelikk (Sep 27, 2007)

I have the same situation, I have a new style harness, for my 2002 chevy. I was told that if I switch the wires on the just the female plugs that this solves the problem. I have not yet had time to test this. Would you be a willing guinea pig?


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## obrut (Oct 30, 2002)

I found the pin outs for the harnesses on westerns web site, looks like it is an easy fix. I will try it and let you know.


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## obrut (Oct 30, 2002)

Ok here is what I did. 
The connectors going to port 3 and 4 on the isolation module need to have two wire changed around. They are the light blue and the blue wires. On the 27780 harness for the 03 to 07 years J is blue and K is light blue these need to be swapped. The 8437 harness needs J to be light blue and K to be blue.

On the other side of the harness where it connects to the head lights the female plug going in between the vehicle harness and the head light needs to be swapped from A yellow B blue to A blue and B yellow. Then the male plug that connects to the head lights needs to be changed from A orange B blue to A blue and B orange. This needs to be done on both sides. Now I didn't touch the bright lights even thought the schematics show those wire reversed as well. I didn't switch the bright lights because the bright lights worked. 

Now when I connect the plow all the lights work like they should. The only thing I noticed is that the low beam plow lights seem dim. I'm going to reconnect the plow later and check the low beam power with my meter to see if I'm getting the 12V I should be getting.

The only thing I wonder about is the high beam wiring, I didn't switch it and it works great.


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## obrut (Oct 30, 2002)

Ok I just came in from checking and I do have 12.85V at the plow light connector with the low beam light on. I guess there just the old style lights, it just seems to be a lot more dim than my truck low beam light.


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## snowpoe (Nov 23, 2005)

Obrut What is a NBS GMC 2000 What does NBS stand for?

The reason I ask is that I have a 01 1500 silverado & I have Western ultra mount wire harness off a 06 1500 silverado

Will the wire harness changes you reccomended work for what I need to do. Get the 06 harness to work on my 01  Im guessing it will work & seems to be an easy fix payup But want to be sure 

Or if I can should I just trade harnesses & get what is made for my truck

I am fine with changing the wires around , but just want to be sure Im not going to fry something as the harness I have is like new & I would like to keep it


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## obrut (Oct 30, 2002)

NBS = new body style

Back in 2000 you could get the old body style (OBS) that was the 1988-2000 looking style as well as the 2000-2007 new body style (NBS). Just like the 2007 you could get both styles.

Go on to westerns website and do the quick match for your truck and the truck that the plow came off of. At the end of the quick match it will show the part numbers for the plow, harness, etc. Write down the numbers for each truck and compare. The only difference should be the headlamp harness. It should be the same as what I have but you will want to double check first.

You could get a new harness if you want, but this is a very easy fix. If you need help, let me know.

Tim


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## William B. (Jul 22, 2004)

Hey Orbit. I'm in a similar situation. I need to make an 01 harness fit an 04 truck. When you switch the wires, are you just cutting them and then splicing the wires or are you actually moving the pins? If so, how do you get the pins out to switch them?


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## obrut (Oct 30, 2002)

I'm just moving the pins. All you need is a small pin or something to use to remove the pins. Maybe you and santelikk can work out a trade, he has the reverse of what you have. Check a few replies up in this thread.


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## santelikk (Sep 27, 2007)

*Trade*

William B,

If you would want to trade let me know asap. I was going to try to get the truck wired this weekend, but it you want to trade, I'll hold off on the install.

Kevin


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