back to basics, RELAYS

[LSXmyford]

Need to double check something.

This is about the most basic question you could ask but just to test my sanity...Im gonna ask anyway.

The truck is a 96 gmc, a nelson harness with a 03 5.3/4l60e

On the nelson harness, there is a fuel pump relay with four wires, three are embedded in the harness, one red wire is free and needs a home.

We went to connect the red wire to the fuel pump, as it is the fuel pump relay ~ power.

Before hand, we test the red wire, key on...

Get NOTHING.

The relay clicks with the key turned to on position....so we test....

There are four wires on the relay. We tested as follows:

orange...is getting constant power
black.....ground
green...gets switched 12v
red....nothing
again, there is an audible click when energized

Correct me if I am wrong but this is a bad relay?

This has been one source of confusion from day one, as we expected power at the red wire but didnt get it, we threw this question out to all parties involved but didnt get a response...I just want to clear this up, so we can move on.

Thanks.





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[NITROUS]

Did you hook the green wire to the PCM, it's what controls the fuel pump. I'm not trying to ask a stupid question, just getting all of the facts together.

Orange goes to the fuse box under the hood and the fuel pressure switch - Pin 87 on the relay
Red is the fuel pump prime connector - Pin 87A on the relay
Grey goes to the fuel pump and the oil pressure switch - Pin 30 on the relay.
Black and white is your ground - Pin 86 on the relay.
Dark green and white goes to the PCM - Pin 85 on the relay.

I haven't messed with a Nelson harness only modified factory harnesses to work. If it's wired like I posted here it should work fine. What's your oil pressure when you crank the engine over? Oil pressure has to satisfy the circuit to engage the relay but I'm sure you knew that unless it's bypassed somehow.

[LSXmyford]

On this relay there are only four wires. On the nelson harness, you only worry about the red wire that comes out of the relay marked "fuel pump relay", the other three wires are embedded into the harness all neat like. there is another relay but the wires are connected by nelsons and embedded into the wiring harness, these wires go to the fuse block on the new harness.

On the relay in question:

The orange is hot all the time, verified.
The black is ground, verified.
The green goes hot with the key forward, verified. (yes it comes from the pcm)
The red, does nothing, ever.
To further add confusion, the relay does click as if it is functional, when the key is turned on.
There is no gray wire on this relay. We were told to connect the red wire from this relay, to the gray wire on the chassis that runs to the fuel pump but the red wire is and always was, dead as hell and that never made any sense...only logical thing would be that the red wire powers the fuel pump but no one will verify this, the closest we got was "I dunno" or "goes to the gray wire", then when it was mentioned the red wire was dead as hell, I guess it was assumed we were ignorant hillbillies, as thats were the conversation ended. All I want to hear is oops, bad relay, sorry, replace it and connect it to X and your fuel pump will work fine.



96 gmc and 03 5.3

[r6z4o6]

If it is a 5 TERMINAL relay, it looks like the red wire is on terminal 87A instead of 87.

Do a wiggle test. Ive never seen a nelson harness, but i have had some terrible experiences with relay "harness" where the wire comes unsolderd from the harness female connector to the relay. What a paiiiin.

Relay's aren't that expensive. You could get one for 5 bux and swap it out and find out if the other one was non-functional. Replace it and connect it to gray wire on chassis and your fuel pump may work fine.

[LSXmyford]

it has five terminals we shall see....

he tried to get a new relay....long story short....got tired of dealing with the fella behind the counter.

[NITROUS]

Looks like the Nelson harness isn't quite made as an orignal replacement harness. Let me explain why you want the 5 pin relay and you can still put one in place of the 4 pin. The 5 pin acts to prime the fuel pump when the ignition is turned on and once the coil builds it releases the contact from 87a to 87 engaging the contacts. My only concern is if you tie 87 and 87a together that the fuel pump and prime will run togther and reduce pump life. You can try hooking up the fuel pump without the prime and not hook the wire to anything but it was put there for a reason. I'd go get a 5 pin relay like I posted a few days ago and put it in place of the one you currently have or talk to Allen and see what he's been doing. It might run fine without the prime wire and that's how Allen designed it, myself I always try to wire things up like they were from the factory. This is one reason I'd like to take a Nelson harness, make it plug and play and send it back to him so every thing including the ABS could be tied into it. I know it's not cost effective to make 5 different harnesses when you can have 1.

[ff_jeff]

it has five terminals we shall see....

he tried to get a new relay....long story short....got tired of dealing with the fella behind the counter.

Thats because the jack holes dont know how to do anything but look up part numbers. I tried to get a relay from them and they couldnt get me one unless I gave them a part number. WTF?!?! A relay is a relay.
I thought 86= ignition, 87= power to fuel pump, 85= ground, and 30=power supply.

[NITROUS]

You're correct Jeff but most 96-2004 have a 5 pin relay instead of the 4 for the fuel pump prime wire.

[NITROUS]

BTW, here's the numbers to an external replacement relay and pigtail like I use.

relay pigtail # is Delco PT1205 and the relay is Delco 15-8719. You can't buy this Delco component as one.

[LSXmyford]

I better correct something. The fuel pump relay in the nelson harness, has five terminals on the relay itself, however, on the electrical connector it attaches too, theres only a place for four wires, so there is no way to connect the red wire to the wrong relay terminal.






actually, he kept telling the parts guy that he just wanted to see the relays, the guy persisted he needed a make/model, bro said it didnt matter its not the same, finally, he gave the make model (03) the engine came out of, the guy told him, hugh, this truck doesnt use the type of relay you have....no kidding....


now he cant find a replacement, all the parts stores want the make/model, they cant use the part number...until nelsons tells him what vehicle to use as reference, hes at a standstill. he can get the pump to work on the old harness but after paying a nice chunk of change for this gem of a harness...wants the dang thing to power the fuel pump.



I asked my bro to post the fuel pump schematic, yall can look at it and give the nod as to where the red wire should go.






we just want the damn thing to start.




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