Okay so I got a bit further in this project. I hooked up a push button starter which is pretty cool, now my problem is that the fuel pump keeps priming as long as the key is in "on" position.

So I have the black, grey, and purple wires fed to the cabin so I can connect it to the fuse block of the LS swap harness. Only problem is, I can't seem to find where the wires are supposed to go. I have the black wire grounded just fine. The purple and grey wires are the ones giving me fits. It just seems no matter what I plug them to, they don't stop priming. When I plug them into the relay box on the side of the LS fuse box, nothing happens at all. Is there something I'm doing wrong?

As it stands right now, even when I leave the pump priming, my engine just cranks but won't start. I've tried to find this solution on every youtube video and wiring diagram(which make no sense to me at all), but no luck.

 

You are correct on the ground. The purple wire is from the sending unit to the fuel gage. The gray is power. Where is the gray wire going? Factory location? Or do you have routed somewhere else. In stock form key on will prime and then stop. When you roll the key to start the relay again will send power through that gray wire. What pump are you running? Anything larger than a 255 won't run well on the factory wiring.

 

I’ll take a shot. After reading the above, I would venture to guess that you have connected the gray wire from the pump directly to power without a relay. The gray wire should be used as a trigger wire from the ECU to a relay and a larger gauge wire and fuse from the relay to the fuel pump. While you are there, you should increase the gauge of wire for the ground circuit. There should be 2 wires from the fuel level sender, usually purple, or purple and black, which should be twisted along their length to avoid interference since the fuel sender is a simple coil that transmits an ohms reading, polarity should not matter. Work through these issues and you should be closer to firing up your engine.

 

Thank you for that input bro. Right now, I have the grey wire plugged into the LS harness' fuse box. Since the fuse box is getting constant power, im guessing thats NOT where its supposed to go. Seperately, I have the original factory ignition wire, a constant 12v wire, and LS key-on/cranking wire plugged into a push button starter, thats why the engine is able to crank. Just for giggles, I tried to move that grey wire to the push button switch and still get the same constant priming effect.

 

Ok, now we have something to work with. The coil of wires marked “Under Dash Wires” is where you are going to find the gray fuel pump trigger wire. Where is your battery located? This will determine where the pump relay will be located. The gray trigger wire is a low amperage connection and can be run a longer distance safely. Did the LS harness come with instructions? This would come in handy for the other wires in that coil of wires.

 

So I followed LSXMatt's rear battery mount idea and put the battery in the trunk and a positive charge bus bar under the hood so I can connect all the stuff to it.

Now with the grey under-dash wire from the LS harness, where is that supposed to go? Do I connect that to the grey fuel pump wire? A 12v source or somewhere else? And lastly, the purple wire for the gauges? Where to for that one?

 

With the battery in the rear, you should run a 10 gauge power from the charging circuit to a 87 on the relay and then to the fuel pump to 30. Ground the relay 86 and the fuel pump to chassis. The gray trigger wire from the ECU goes to 85 on the relay. You should have a bulkhead pass through behind the rear seat, under the carpet. This is where you will run the fuel gauge wires and the fuel pump trigger wire. Mount the fuel pump relay and fuse holder next to the battery. Hope this helps.

 

Im gonna try this tomorrow after work!! Thanks man! I'll let you know how this goes!!

 

I want to make sure im doing this right. I have a relay box with an 87, 86, 85, and a 30.

I want a 10g 12v wire going from the positive bus bar to the 87, the grey wire from the fuel pump goes to the 30, the fuel pump's ground wire goes to the 86, and the LS harness' grey underdash wire goes to the 85?

 

Ok, we’re close. The grounds (there are 2) one for the pump and one for the relay terminal 86 are independent and go to the chassis. The original 12v wire to the pump is not an adequate size to run an LS fuel pump, this is where the 10 gauge wires will need to be upgraded. There should be (2) 10 gauge wires, one from the buss bar to terminal 87, and one from terminal 30 to the pump. This leaves the gray wire from underneath the dash, from the ECU to trigger the relay at terminal 85. You can use the original 12v wire (gray) from the fuel pump to trigger the relay (85), which remains through the bulkhead connector to the dash and connect it to the gray fuel pump signal wire in the LS harness from the previous picture. One last note, you will need a 30 amp fuse between the buss bar and the relay. All of the new wires (2) red and (1) black 10 gauge are in back and connect to the fuel pump via the relay and the original gray and black wires from the fuel pump will be repurposed to the relay to trigger the pump from the ECU. I hope this clarifies things.

 

Okay so I think I have it figured out:

-10g wire from Busbar to 87 with a 30amp fuse between.

-10g wire from 30 butt-connected to the fuel pump's grey wire

- Ground wire from relay's 86 to the chassis

- Ground wire from fuel pump to 86 (or also to the chassis?)

- Grey underdash wire to 85. (Am I understanding you right in joining both the factory grey wire and underdash wire before connecting it to 85?)

- The factory fuel pump's purple wire goes where now?

Man listen, I really appreciate this help. Bolting engines together and all that is easy, but this wiring stuff is an absolute nightmare to me.

 

Engine ECM controls the prime. If pump won't shut off then it means the ECM is not controlling the pump, and you've accidentally wired pump or relay to always be on.

That might be a master of the obvious reply, I didn't read the whole thread.

 

After seeing the latest post, I am thinking that you have not replaced the fuel pump and you are using the original TPI pump, so my response will reflect this. So far you are starting to understand what you need to do. The relay connections are correct now, but since you are using the original pump, there is no need to run a 10 gauge lead from the relay to the pump. Connect the gray wire from the pump directly to terminal 30 on the relay, splice a length of the gray wire from the LS harness (you will have extra after splicing the ECU wire under the dash) to the gray wire from the rear of the rear bulkhead to terminal 85 of the relay. The original pump is probably already grounded, so you will only need to ground the relay at terminal 86. The 12v source from the buss bar does not have to be 10ga at this time, but will be best for future upgrades. At this point you are finished in the back of the car and will move to under the dash. The original gray wire that comes through the bulkhead to the dash will be spliced to the gray wire from the LS harness and you should be able to prime the pump when you push the start button if it is connected correctly. Think of all of this as the ECU wants to turn the fuel pump on and the relay acts as a switch for it to do so, it’s that simple. Hang in there, you’ll get this.

 

One more thing, the purple wire is your fuel level sensor.

 

Welp, I tried every way and configuration you mentioned and got the same result everytime. The fuel pump just wont prime at all. And that's not a knock against you at all so don't misunderstand me, you've been very helpful. The problem is something I've clearly done wrong or failed to do at all. So I resoldered the factory fuel pump wires to the factory locations and buttoned it all back up. This project is just not happening and Im really just over it. I'm just gonna go look for a for an external fuel pump LS setup.