Remington H.

iTrader: (2)

I am just about finished with my engine swap. I am swapping a 6.0/4l80e controlled by a stand along wiring harness, into a fullsize blazer (previously a 350 tbi) and have everything ready to go and wired up except for the fuel pump relay. I have a friend who helped me with some of the wiring that I had some trouble with, and he said that instead of using the new fuel pump relay that came on the stand alone wiring harness, that I could just use my stock fuel pump relay since it is controlled by the iginition and is already wired up. And my question is if this is a good idea or would I be better off just wiring up the new relay, because if I could use the old relay and be trouble free, then that would be awesome. Any help or advice would be much appreciated.

Thanks,
Remington

LS1XJ

Whose stand alone harness is it? Idealy you want the fuel pump controlled by the computer, Or at least connect the wire from the computer that sends the fuel pump signal to your stock relay. This is just my opinion. Though, Iam sure you could just connect it to your stock relay if you really wanted to.
Dustin

crainholio

iTrader: (2)

I used my old TPI fuel pump relay and connector, just wired the LS1 PCM's relay control wire to the appropriate pin.

Be aware the LS1 manages the fuel pump relay by cycling voltage...whereas on the fans, it cycles ground. Not sure how your TBI relay is wired, you'll want to check to be sure.

Speartech

iTrader: (14)

Yes that will work fine. Just take the green wire from your harness and tie it to the green wire on the relay that is already on the blazer. That way all of your fuel pump wiring that is on the blazer already will still be used.

Remington H.

iTrader: (2)

Ummmmm, LT1350.com did the harness, and there is no green wire on the relay. There is a black and white coming from the harness to the relay, and a blue and yellow going from the relay to (power and pump I am guessing). And the guy said that he wired the relay so that the two wires were interchangable, I guess for ease. So what your saying is that I can wire either the A.(blue, or yellow) or B(black, or white) for the computer signal to go to the old relay. And just leave the wiring to the old signal alone except splicing into the green wire?

Thanks,
Remington

Speartech

iTrader: (14)

I don't know on that odd color coding, but it sounds like the black or the white would be the signal wire that you could take to the green of your old relay. You just need to figure out which wire is which. If you have a meter or something or a test light you can determine which wire you want. Of the 2 wires one is ground and the other is the signal wire from the computer and it is +12 volts for 2 seconds when you turn the key on.

Remington H.

iTrader: (2)

So whichever one is the ground, should I splice it into the ground on the relay? or just ground it?

Remington

Speartech

iTrader: (14)

If both the new harness and what's left of the old system are grounded, you shouldn't even need to mess with any of that. If you can just determine which wire is the signal wire (+12 volts for 2 seconds with key on) and move that over to the green wire of the old relay, you should be good to go.

Remington H.

iTrader: (2)

Thanks, hopefully I will be firing it up tomorrow or Sunday afternoon and breaking in the engine, and thanks again for all the help.

Remington