seems repetitive but all headlights on an 02

[snowboardman137]

alright i have an 02 sierra and i really wish when i turned my high beams on the low beams also stayed on... like when you hold the switch back. i have hids in my lows and when you hold the switch back it is alot brighter and i really wish it was like that with my highs... ive heard of a diode between somewhere for my highs and lows? other question is if it will hurt anything? this place has like the best help so i figured id ask here, even though it seems to be a repetitive question...

 

[Unit453]

Here's some instructions but I'll see if can find you some pictures.

Pull the underhood electrical center cover off, place aside. Unbold the four bolts holding the drivers side corner brace (fender to firewall) and remove. This is to remove the cover surround on the electrical center. Gently pry the plastic snaps holding it in place. There are two between it and the fender and two large hooks toward the passenger side at the bottom. Now lift off the plastic cover for the electrical center. You will see two clips holding the electrical center close to the fender side while the two toward the passenger side are hinges. Release the two by the fender and roll the electical center towards the passenger side. The mess of wires will tug a little but it will roll over to expose the underside. Looking at the right underside you will see a grey wire block. There are small letters and numbers identifying the wires. Look for D3 and you will find a yellow wire. This is the control for the low beams. Is is switched ground on the 01-02s unlike the 03-04s. All you need to do is get a scotchlock (or solder if you prefer) and tap the yellow wire to ground. I ran it in a loom up to the ground studs on the firewall (follow your underhood light wires down if you can't find one). That's it, test it out and fold the center back down. Recover and replace the brace.

There are three main components. The headlights, the High current relays and the BCM. The headlights are actually powered by the high current relays contacts. The coils of the hi current relays are powered by 12V on one side of the coil. The other side of the coil then goes to the BCM. The BCM then uses the equivalent of an open collector transistor to "sink" the relay control voltage to ground. When the transistor is tuned on current is allowed to flow and energize the headlight relay.

If you were to measure the voltage at the BCM connection when it is not on you would see +12V. This is why you need to apply a ground to make them come on.

Problem is you do not just want to add a wire. If you add a wire and tie the lows to the highs you will also get highs when on Low. That is why the diode is added. The diode allows current to only flow in one direction. So to make other light circuit control relays to operate on high also you need to put in a diode between the Low relay BCM wire and the high relay BCM wire. The diode cathode always connects to the high beam relay BCM wire.

The diode can be added at either the bottom of the relays or under the dash near the BCM. My mod does them at the BCM. Others will show you pictures of the diodes under the relays. Both work because diodes are effectively on the same wire.

This is the best I can come up with for now. Unless someone here has done this with an 01 or 02, I'm really not sure how it works since the electrical systems are different.

 

[83GMCK2500]

Dave's Sierra HT is an '02, I'll make sure he sees this...:thumbsup:

 

[88gmctruck]

This is the best I can come up with for now. Unless someone here has done this with an 01 or 02, I'm really not sure how it works since the electrical systems are different.

Nick, the first set of directions you posted are correct. If you simply ground the yellow wire D3 your lowbeams will stay on with the highbeams.

I wired my 02 the same way, however, instead of tapping the wire with a scotchlock and running it to a ground, I repositioned the pin to an unused place on the block that was a constant ground. I don't know which socket i moved it to, however a test light will tell you where you can relocate the pin to. You can always just run your own ground wire.... Either works.

If your still lost I might be able to pull my truck apart, if i can find time.

Dave's Sierra HT is an '02, I'll make sure he sees this...:thumbsup:

):h

 

[bigdisneydaddy]

There is a screw (10mm head) on the inside of the box that holds the plastic electrical center to the inner fender, I always ground to this screw, that way everything is under the cover and you will never see it. The screw points towards the outside of the truck, horizontal, just about centered in the box, remove it and attach the wire with a ring terminal and a start washer and replace it for a good reliable ground. I have done dozens of these for friends and never had a problem.

 

[snowboardman137]

alright so im a mechanic and all but im sorta confused... let me get this straight... i need to ground the yellow wire in my fusebox and i also need to put a diode between the relays? im sorta worried about shorting out my bcm... i guess i wont attempt it until im sure i understand everything... lol...

 

[88gmctruck]

Diodes are for 03+ as they use a different system than 99-02 trucks. 99-02 don't use seperate relays for high and low beams to switch the headlights, but instead one relay to power the headlights and a ground switched by the headlight switch/dimmer on the column to go between high and low beams.

Just ground the yellow wire and you'll be good to go.

 

[snowboardman137]

alright gave it a shot... AWESOME! easy install also... only took me like 20 mins and that was reading the instructions the whole time... thanks unit453 and 88gmctruck for clarifying that for me... havent tried em at night but im sure it'll make a huge difference... def. since when i switch to my lows i dont have to wait that 15secs. or so for my hids to warm back up...

 

[Unit453]

when i switch to my lows i dont have to wait that 15secs. or so for my hids to warm back up...

Thats always nice. I have HID's in lows, highs and fogs. If I could do it again, I would've skipped the high beams. I dont run them nearly enough anymore to justify having them.

 

[88gmctruck]

alright gave it a shot... AWESOME! easy install also... only took me like 20 mins and that was reading the instructions the whole time... thanks unit453 and 88gmctruck for clarifying that for me... havent tried em at night but im sure it'll make a huge difference... def. since when i switch to my lows i dont have to wait that 15secs. or so for my hids to warm back up...

Not a problem

Thats always nice. I have HID's in lows, highs and fogs. If I could do it again, I would've skipped the high beams. I dont run them nearly enough anymore to justify having them.

I also have HIDs in my lows, highs and fogs and i completely love having them in the highs. I get tons of chances where i live to run them for long periods of time, so it's totally worth it. Plus the HIDs in highbeams are just rediculously bright.

 

[snowboardman137]

alright i just drove with em and they work awesome... now i just wish my fogs didn't shut off with my highs still... lol... anybody have a way of keeping them on also?

 

[496 BB]

Easier way to do this is to ground the yellow wire of your passenger high beam. Thats it.

 

[prican_2000]

99-02 don't use seperate relays for high and low beams to switch the headlights, but instead one relay to power the headlights and a ground switched by the headlight switch/dimmer on the column to go between high and low beams.

Just ground the yellow wire and you'll be good to go.

Can you give me more information on this^

where can I locate this Yellow wire that needs Grounding????

THANKS

 

[88gmctruck]

You can simply ground the yellow wire at one of the headlights themselves, or the other option (which I did) is to ground the connection under the fuse block. The connector is C4 (green), in position B3. You can pull the contact out and either snip it off and gound it elsewhere or find another contact that is constant ground.

 

[prican_2000]

Thanks David!

Fuse Block under the hood not in the cabin - correct?

 

[88gmctruck]

Yes, under the hood.

 

[prican_2000]

^^ Thanks David!

Don't be surprised if I have more answers, This is my 1st Pick-up so I'm kinda new to this world.