Can anyone please post the schematic for a 2004 GMC Serria 2500hd? I wish to use a relay to get both high and low beams on at the same time without increasing the current draw on any one set of contacts.

don't need a relay, just need a diode. check this thread

http://dieselplace.com/forum/showthread.php?t=12804&highlight=headlights

Jim

Diodes cause twice the design current to pass through the highbeam relay contacts. This can cause overheating and spark weld the contacts together.

Diodes cause twice the design current to pass through the highbeam relay contacts. This can cause overheating and spark weld the contacts together. ???? You don't seem to grasp the concept. Each relay is activated and each realy handles it's own load. The diode is on the COIL(#85 to #85) side of the relay, NOT the CONTACT side of the relay. Perhaps if you read the post you would have understood this. But if your bound and determined to screw things up with a relay, try wwww.gmupfitter.com for wiring diagrams. Remember, one side of the coil is hot all the time, the other side is grounded in the BCM. That is why the diode works and does not impose any extra loads on the CONTACTS.

Jim

Well I guess being a electrician I wouldn't know anything about wiring. Look at your own link above and the pictures that are there clearly show that the diode was soldered between the power contacts (30 and 30) and not the grounded side of the coil of the two relays. There is a diagram of the internals of each relay on the side which is clearly visable. And if one was to use a diode between the coils on the grounded side then yes it would work but then the solid state switch inside the BCM would be energizing two coils wouldn't it? Twice the design load again. :ro)

On another note thanks for the website info. It helped out alot.

Absolute

I used the relay myself. Went to the BCM right under the dash and installed it there, using the ground of the BCM high beam side as the relay trigger for suppling ground to the low side.


EDIT: WTF wont these schematics resize right Censored Censored Censored Censored Censored Censored

http://service.gm.com/engif/000/001/247/1247982.gif

hey absolete, you tell me What is the design load on the bcm high beam output? take the time read the Whole thread. alot of folks have done the MAX mod including myself, i have yet to buy a new bcm:wtf1:

Well I guess being a electrician I wouldn't know anything about wiring. Look at your own link above and the pictures that are there clearly show that the diode was soldered between the power contacts (30 and 30) and not the grounded side of the coil of the two relays. There is a diagram of the internals of each relay on the side which is clearly visable. And if one was to use a diode between the coils on the grounded side then yes it would work but then the solid state switch inside the BCM would be energizing two coils wouldn't it? Twice the design load again. :ro)

On another note thanks for the website info. It helped out alot.

Absolute
Your making a assumption that the pretty picture is aligned with the contacts. Wrong assumption. My relays don't have a pretty picture and I had to turn them over and look at the terminal numbers on the bottom.

If you don't want to go with the diode, fine, then get a relay and kludge up some wiring to get things to work. But then your going to violate your first requirment, to activate two relays without increasing the load on the relay contacts. Seems to me your going to need to drive your aux relay off the contacts of the first relay to activate the second relay. ooops, just increased the load on the contacts, arcs, sparks, and welded contacts.

The diode is easier, quicker, and painless.

Jim

Not if you use the power contacts of the high beams to energize the coil of the aux relay and then parallel the aux power contacts with the power contacts of the low beam! I have already draw the schematic and if I could remember how to load it onto this page then I would show you.

Now peekok, the name is Absolute, lets not act like children and start degrading each other, if you can't disscuss topics like an adult then stay out of it. When gm built the truck I'm pretty confident they did not intend for diodes to be used so that the stock bcm electronics were to be used to energize twice what was originally there. I am just trying to develop a way that does not increase electrical load on any one component thats all.

Instead of listening to anothers ideas you and jholly seem to think that you designed the truck and know all that there is to know. I work with this type of stuff at work all the time and know a thing or two about relays and electronics. If you wish to use diodes then go ahead. I never said that it would harm anything I just said that there may be a chance. I just don't see it as the best way thats all.

Sure would be a boring world if everyone had the same ideas and thoughts wouldn't it?

hey absolute thats whats great about this forum, its a place people can go to gather and or share information about thier trucks. basically the thread jholly reffered you to talks about different ways to acomplish the same product, or variations thereof. everyone that read the whole thread understands that in this case you would be sinking twice the current of that output but it was within the limits. one thing ive learned in my 26 years as a wireman is if you put 100 electricians in the same room and layout each man with the same task, you will end up with 100 different products. if your looking for the most simplified, less complicated, best looking, cost effective, safest, way to do this mod, 1 diode is all you will ever need. :ro)


BTW if i mispelled your name im sure it was nothing personal.

Well peekok if I believe that it will cause no harm then I too may end up using the diode method. My end Idea was to open the fuse box and do all the wiring where it could not be seen and use a spare location for the aux. relay, I just thought it would look better that is all.


Peace

Absolute