91 Suburban/Crew Cab Relay Harness

[monte0185]

Hey everyone. Im swapping my 86 Dually over to a 91 Burb front core support and need some info on the headlight wiring. I have my old wiring and I also have a relay harness for the 86 headlight setup but since the headlights have different connectors I was wondering what everyone was doing to wire theirs up. Are you using a different relay harness if so what part number or are you just swapping the plugs on your old harness? Ive read some people just swap out the whole harness from the firewall and that would be great if i had the 91 harness.

I have a brand new set of headlight pigtails so Making my own relay harness is not out of the question. Im not sure how I can make the low beam and high beam both light up on the brights i guess is where im having the most problems since the older low beam lights had 3 connectors and not 2.

So everyones opinions and help would be great.
Thanks in advance!!

[monte0185]

Think I found out how I can do it but I'm going to loose my low and high beam lights at the same time. Wish the newer lights had 3 connectors on the low beams to be able to connect the low and highs together. This a pic from my relay harness.

[Just call me Sean]

Single headlight trucks have a low/high beam, 3 prongs. Then your '86 have a low (3 prongs) and a high (2 prongs). Low still stays on when on high. I was thinking of using a low/high in place of the low to have four high beams. For the '91 where they're both 2 prong you could use a relay triggered by the high beam to power the low.

[monte0185]

Originally Posted by Just call me Sean

Single headlight trucks have a low/high beam, 3 prongs. Then your '86 have a low (3 prongs) and a high (2 prongs). Low still stays on when on high. I was thinking of using a low/high in place of the low to have four high beams. For the '91 where they're both 2 prong you could use a relay triggered by the high beam to power the low.

Using the relay to power the low is the best solution I think just got to rewire the relays I have I guess. Was hoping to avoid rewiring them but oh well I guess.

[Just call me Sean]

You would need to wire them normally, then add a relay just for turning on the low when on high.

[monte0185]

Originally Posted by Just call me Sean

You would need to wire them normally, then add a relay just for turning on the low when on high.

Surely you can power the low relay with the high relay on a harness. Still working on the logistics. Might have to use a zener diode to prevent back feed or use a 3rd relay. Still working on my diagram. Here is what I have at the moment. The blue on the right is the high beam relay.

[Just call me Sean]

That's what I said, use a third relay.

[monte0185]

I Think Im going to run a diode in between the signal wires on the relays instead of running a 3rd relay. This should do what Im looking for but I also have another question. I know the stock wiring was about 18ga maybe 16 on these trucks for the headlights. I think im just going to build a whole new relay harness so given the math I think I can use 14ga on a relay setup. Reason I thinking about running smaller than 10 is cause the replacement pigtails I have are 16 or 18ga as well and i dont think they make 10ga ones. What do yall think?

[gmachinz]

You can run whatever you want for sizes if the terminals allow for it. I build 73-up headlight harnesses and for relay upgrades I use 14 gauge from the relays to headlights with new connectors and terminals. I don't use Chinese pigtails-I pull an entirely new harness from the bulkhead connector forward but I also build splice kits which is a little more cost effective. A diode is much cleaner than using a 3rd relay-the less cluttered the better. The key is to ground the harness extremely well-I use Packard style 10-12ga grounding terminals on both sides of the core support.

[gmachinz]

This is the type of grounding ringlet I like to use-and that is a 10ga SXL ground lead.

[monte0185]

I should have just had you build me one!!! LOL. I already ordered all my connectors and wire however. Im gonna run 14ga from the lights to the relays and 10 for the power and grounds. I like those grounding connectors you had a pic of as well. Do you run seperate grounds off each light or Just ground them all together? Got any pics of your harness's? I like to build my own relay harness's as well for the older trucks with the H4 headlights but I cheaped out and bought one off evilbay the last time. This is the first one I have built for this style of light though and sourcing the headlight connectors is a pain and their only 16ga wire. Oh and im gonna run a diode as well. I got a 50v 3amp one to run in between the signal wires.

[gmachinz]

I have most of the factory GM manuals and almost every example of actual production harnesses so I basically am able to replicate most GM harnesses. As for the headlight grounds, there are two-one on the core support to the leftbof the drivers headlight and on the other end of the headlight harness there is another ground that is secured to the core support along with a battery ground and a lead to frame ground near the fuel pump on top of the frame section. You need to ground everything like GM intended so the lighting has a good path to ground.

[monte0185]

Originally Posted by gmachinz

I have most of the factory GM manuals and almost every example of actual production harnesses so I basically am able to replicate most GM harnesses. As for the headlight grounds, there are two-one on the core support to the leftbof the drivers headlight and on the other end of the headlight harness there is another ground that is secured to the core support along with a battery ground and a lead to frame ground near the fuel pump on top of the frame section. You need to ground everything like GM intended so the lighting has a good path to ground.

I have most of the manuals as well. I usually do my grounds the same as GM did them as well but i like to see how everyone does their wiring. Some people have different styles. Some good some not so good but still interesting. I try to keep mine as factory looking as possible but with some improvments but it still needs to look like it belongs where its at. Thanks for the help. I appreciate it. Oh and post some pics of your harness's Im curious. LOL