back to basics, RELAYS

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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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.

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


:)

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.:D

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.

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.

Quote:

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Originally Posted by 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.

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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.

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

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.

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. :D




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Quote:

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Originally Posted by LSXmyford

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.

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I think I've posted more than once where the red wire goes. That's straight from GM's manual and the way my 97 is setup. Red is the fuel pump prime connector - Pin 87A on the relay. If you want, I'll post the schematic also. :bash: :smile:

This is the 96 C1500 schematic, unless I'm missing something this should be all of the info you need.

well for one, you are missing something, your attachments are too small to see, you acknowledge this in past threads, maybe its time to remedy the situation.

second, your just not getting what is being asked, its understandable, its alot easier for me to see my POV than it is for you to put the pieces together and see my perspective.

im tired of trying for now.

when and if the pcm arrives and a new relay is found, im sure we will post something.

Someone here on LS1Truck will have to correct the file size issue because it's full screen on my end. If you took a picture and posted this 4 pin connector your talking about it would sure make things simpler. You say you have a 5 pin relay correct? If so it would still be wired just like I posted above and shouldn't be any different. I can't explain where the wires go any easier even if you only have 4 wires because you must be missing one which I understand to be the red prime wire. I hope someone can help you out since I'm not able to.

Good Luck!

Are you still getting no juice from the red wire, key on OR key off???


"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."


PLEASE PLEASE PLEASE check that fifth terminal on the relay for 12v when you hit the key:D:D:D:D


Ask for a "foglight relay" at the parts store...I had the same problem and kept getting some 30$ relay until one of the girls who worked there and KNEW what was going on told the little snot nosed oil stock boy where to go, i think they are near the headlights/fuses/lightbulb area and found a generic 30a relay, like 5 bux.

Her is a biggie-size of what Nitrous posted:
http://www.ls1truck.com/upload/files/31/SANY0775.JPG

Here is life-size schematics for 2001 5.3..may or may not be of interest to ya.

http://www.ls1truck.com/upload/files/31/SANY0774.JPG

Terminal 87a is the prime terminal. The only time you should have +12 volts on the prime terminal is when you apply it. It's a test terminal. By applying battery positive (+) voltage to the jumper wire with the relay plugged into the fuseblock, you can verify whether the fuel pump runs or not. This was driving me crazy so I had to verify it for myself, because I was going by the diagram and not looking at my vehicle. You don't need to hook this up to anything even though the diagram shows it.

Quote:

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Originally Posted by NITROUS

Terminal 87a is the prime terminal. The only time you should have +12 volts on the prime terminal is when you apply it. It's a test terminal.

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On my 91 the RED wire PRIME(TEST), it goes to ALDL connector G.

My final absolute end of all problems answer that will fix it for SURE....
The red wire should do NOTHINGGGGG!!!!! When you put 12 volts on it with the KEY OFF, it will put power to 87, which is the GRAY WIRE that you have never mentioned, LSXmyford!!! Probably because it fell off of the mysterious fifth terminal of the relay!!!!!

In conclusion...
================================================== ===

KEY ON, your mystery fifth terminal on relay shows 12volts, yes?????
KEY OFF, you put 12v TO your RED wire, your mystery fifth relay terminal now HAS 12v, yes??
================================================== ================

BTW, this reply is for myself!! :whack::whack::whack: Yep, this wire is about 8-10 inches long and has a small female spade connector on it right behind the fuse box by the firewall going nowhere. I apologize for sounding a little harsh above but I was helping another member and glanced at this schematic not to mention no pictures.

Do you still have the factory original fuel pump relay installed in the truck? You mentioned that when you attempt to start the engine you can smell fuel, if it wasn't wired correctly then you wouldn't be getting fuel. Have you put a fuel pressure gauge on the rail to see what fuel pressure you're getting and if its holding pressure after crank?

r6z4o6

Thanks for the relay info, hes gonna check that out, makes total sense. However, man oh man, I would be lying if I didnt have all kinds of colorful language come to mind when I read your post. Gonna make this short and sweet. There are 5 terminals on the relay itself. However, here comes the key part to this, the pigtail in which the relay attaches, only has four openings, if a person wanted to use the 5th terminal on the relay, they would have to literally drill out the pigtail...there is no missing 5th wire. Stay tuned, cause Im gonna explain to nitrous why I think nelson used four wires instead of 5. Its a theory but a damn good one.




redheartbeat

Yes. We had the fuel pump wired to the old relay/ harness, this is how we know the fuel injectors were working with a cranking engine, yes it holds line pressure. We are trying to eliminate as much of the old as possible, so we are trying to get the fuel relay on the new harness to work. He has recently tried to confirm spark and again, no spark.




nitrous

Reason I didnt post the shematic, I stated this issue would be dropped until the pcm arrived, Im glad you revived it, I have what I believe is reasoning for the four wires.

First off, we found out the gray chassis wire is power to the fuel pump.

Now for the fuel pump relay on the NEW harness.

He confirmed ground, constant 12v, then put a hot wire to the switched wire (green)....

then checked for power at the red wire, again nothing. As stated to r6z406, the pigtail only has provisions for four wire attachment, the fifth is physically blocked. Logically, this tells me, the red wire should go hot with the key forward...Im sure you would agree, its a bad relay, if not, it defies logic.

Now for the epiphany that leads me to believe four wires is ok in this scenario.

My bro put a test light on the switched green wire that leads from the pcm to the fuel pump relay. When he turned the key forward, the 12v switched green wire from the pcm, went hot, then after about a second went dead. I believe the fuel pump prime is built into the 03 pcm programming. Thats the only logical explanation of why that wire would be live, then go dead after a second, it behaves much like you would expect a pump prime to behave and also explain why nelsons only used a four wire connection. I can only assume at this point, should the engine crank and fire, the pcm would energize this green wire as needed, ultimately activating the relay, ultimately sending power to the fuel pump.

Apparently, your five terminal is needed for some damn reason, whereas the 03 5.3 pcm doesnt require it. This is theory, as the engine has yet to idle.



Can we get a group agreement here? :D

sounds like its wired correctly. The PCM primes the pump for a second and then shuts it off until there is a crank signal from the engine to tell it the engine is turning and needs more fuel. If it stayed on all the time then it would eat the battery charge up while there was no need for fuel being pumped. I believe its also a safety feature for vehicles envolved in accidents, sure don't want a fuel pump supplying fuel for a fire.

exactly


I asked nitrous but didnt get a reply, how would a five terminal relay sense a voltage drop or load and initiate one terminal over the other 87 vs 87A, how does that work?

The 5 position relay would switch off from 87a and on to 87 when power is applied to the coil inside the relay. So it sounds as if the 4 wires is correct on your harness. The pcm is looking for a reason to supply fuel(oil pressure??)

It won't see it unless you apply it. 87a isn't hooked to anything so just forget it's even there, pretend you have a 4 pin relay. 87a is a test point on the relay which has to be applied with an external source of power.


When current flows across pin 85 and pin 86 the coil will close contact 87 to 30.

Does this answer your question?

Like r6z4o6 said, I wasn't quick enough.

Wiring schematics are one thing, PCM logic is another.:smash:

Whew I can't wait for this thread to end! :tvhaha: Anyway, I hope things work out.

three pages and 28 posts and we have confirmation, the relay was bad. :D

Omg.

wow!!!!!

Damn, I wish you would've changed out the relay to begin with or just jumper it. The way it sounded it could've been anything. :LOL:

would have but he couldnt find one..finally the harness company give up their secret source of relays...:D


this thread definitely took a direction I didnt expect.


have a new thread in the electrical section, check it out.