Key on and cranking wire
 

Have a wiring issue somewhere or I have something hooked up wrong. Installed a 99 4.8 in my 72 c10 that had a 350. Used the pink wire coming off the bulkhead as shown in the photo to give me key on and cranking power and to power the fuel pump relay. Engine starts and runs fine, until after about 30 seconds the pink wire starts to get hot and will burn up if I don't shut it down. What did I do wrong?

Re: Key on and cranking wire
 

Just a point to add , wire does not get hot with key on and not running, only when truck is running.

Re: Key on and cranking wire
 

is this a homemade harness?
my fuel relay is run by the ecm

Re: Key on and cranking wire
 

Harness is a PSI knockoff that I picked up off Ebay

Re: Key on and cranking wire
 

How is your alternator wired

Re: Key on and cranking wire
 

Thru the swap harness

Re: Key on and cranking wire
 

On all my LS swaps I've used aftermarket harnesses and they all had a relay for the fuel pump. As said above the ecm sent the signal to the relay. I don't recall if the ecm supplied the ground to the relay or if it was 12 volt positive to the relay.
I could be totally off base but does that pink wire supply 12 volts to all needs in the truck? Adding an electric fuel pump to the load could be a bit too much.

Re: Key on and cranking wire
 

Pink wire comes from the key switch, it is hot in run and crank.I currently have it supplying the starter relay and the fuel pump relay, is this my problem? Where else should I tap into for 12v constant power for the fuel pump?

Re: Key on and cranking wire
 

You said you have a psi knockoff..and I think your instructions are also copied from psi
On a real psi harness the fuel relay is in the fuse block...you shouldn't have to wire any hot to it..
Its fed thru the fuse block

A ??...why are you feeding 12v to the fuel pump relay?

the only wires on the relay that the user connects are the ones going to the pump...
there are only 2 12v wires you need...a switch on 12v, and a constant 12v
You can get your constant 12v from multiple sources that are on the truck..

Re: Key on and cranking wire
 

Ok, this helps. I do have the instructions, but I was confused by them and thought I had to power the fuel pump relay also. I will take a look at it and correct it. Thanks for the help, I appreciate it.

Re: Key on and cranking wire
 

Is that the original resistor wire that went to the coil? If it is, it's best to replace it with a standard wire.

Re: Key on and cranking wire
 

So looking at the instructions that came with the harness, fuel pump relay does not come pre-wired. I have to supply feed wire from a constant power source and output to the pump.The keys with wire that is for the starter relay apparently won't work, it gets hot. Recommendations on where to power the fuel pump relay from?

Re: Key on and cranking wire
 

Ok..this'll show how good I cant remember...the constant 12v does go to the fuel relay,,pin 30....should have looked at my drawing 1st...sorry
On one truck I came from the firewall junction under the hood, which comes from the battery
The other I used a heavy junction block, that comes straight from the battery..it goes to the fan relay and the constant 12v

Re: Key on and cranking wire
 

The pink wire from the truck should power the main key on power relay (LS swap wiring harness) only. Fuel pump relay is powered by constant 12v source (through a fuse) and triggered by ECM.