Need some help on how to wire in the hot wire to fuel pumps with a dual tank setup

[UATahoe]

Looking for some help guys. My 87 pickup was a tbi truck that had dual tanks. I am trying to figure out where the hot wire from the fuel pump relay should tie in.

Also, is the original fuel pump relay on the 87 right on the firewall pretty much dead center? Should I just use the existing wire form that relay and use it for the new relay? I had the original ls1 harness reworked as a standalone and it came with the fuel pump relay weird in.

[Robznob11]

You should not need anything to do with the stock relay. Your reworked harness should be stand alone you should have a relay that is tied into battery power there is a wire from the computer that will fire that relay when you hit the key. Also when I wired mine I went ahead and used the computer ground like the factory had it. I would recommend that you run a 10 gauge wire from the battery to near the pump and add another relay. Use the fuel pump relay they wired to fire the one near pump. This way your pump gets a lot more juice and less chance of starving for fuel. It's basically like a hot wire kit. Most people who rework harnesses rely on small wire just like the factory did and it's just not up to par. For 60$ racetronix sells a universal Hotwire kit and it's well worth the money!!! It's plug and play for the most part you will have to modify it if you are running your stock pump. But even there I would suggest you upgrade. I have seen trucks idle at 58 psi but when you load them they will drop to 40-45 and run lean. Then people can't figure out why it pops through the intake above 4000 rpm. I hope this helps

[BR3W CITY]

x2 on running a heavier gauge wire for the power-side feed on your pump wiring. The "trigger" to the relay from the key (or ecm, depending), can still be small, but the "contact" side of the relay that supplies power to the pump NEEDS to be a 10+awg wire.

Aftermarket pumps can draw a bit more than some cheap relay kits are made for, and you can actually feel the small awg wire heat up from resistance. This isn't safe, nor is it good for the pump.

[foamypirate]

The guys above have good advice, but if you are intent on using the stock wiring, you would tie into the tan/white wire on the left side of the bulk head connector in the engine bay. That wire goes through the bulkhead, through a fuse, and back out the bulkhead with the rear wiring harness, and splits to a connector that runs to the dual tank switch through the firewall. The other side of the split goes to a plug with no terminated connector in the other end, on a dual tank setup (if it was a single tank, this would be terminated for use on the driver side tank). For what it's worth, I know several people running the stock wiring with no issues. That's not to say the upgrade isn't worthwhile for peace of mind!

You can see the wire a little bit here (tan/white spliced to gray). Pardon the mess, I haven't cleaned everything up.

[UATahoe]

Thanks for the advice guys. Once I dig in to everything, I will see how things look. The reworked harness uses really good relays and I will make sure the hot wires are adequate.