New fuel pump relay

Scrapla347 · Nov 3, 2025

I have a 1990 GT and installed a Holley Terminator X. I'm running a new fuel pump relay to the rear hatch area. I've watched videos and a lot of people mount their relay outside the car underneath where the fuel pump harness is. I want to mount the relay inside my hatch where the spare tire is. My question is can I just ground that relay to the body inside my hatch and leave the factory fuel pump ground alone? I have a 255 in tank pump with factory wiring. On the videos I watched they removed the fuel pump ground from the pig tail and grounded it to the tank strap mount with a ring terminal and self tapper. I don't want to touch my factory fuel pump ground and just ground my relay inside the car next to the relay. Also any suggestions on where to ground inside the hatch? I see some people use a bolt and nut to make a ground post.

AeroCoupe · Nov 3, 2025

I put one in the trunk (Coupe car). Used some 200 grit sand paper to clean a 1/2” x 1/2” area to bare metal and bolted it down. Hit it with some black spray paint and it’s been good for about two years now.

Scrapla347 · Nov 3, 2025

I was going to use a ring terminal and self tapper into the pan OR run the wire out the grommet and self tapper it to the tank strap mount near the rear bumper like I saw in some videos. From my understanding the shorter the better.

Scrapla347 · Nov 4, 2025

On all the videos I see they are mounting the fuel pump in the rear but can I mount the relay under the hood and just run the power wire to the rear?

Sparky714 · Nov 4, 2025

Scrapla347 said:
On all the videos I see they are mounting the fuel pump in the rear but can I mount the relay under the hood and just run the power wire to the rear?

Yes, shouldn't be any problem doing that. I have an '89 I'm currently upgrading the fuel pump on and I'm mounting it under the drivers seat next to the stock relay. The Aeromotive harness I'm using was set up for under hood mounting, but I don't want it there, so I modified it.

AeroCoupe · Nov 4, 2025

Assuming you are no longer using the stock harness so put it where it makes sense. I put mine in the trunk as I used the factory wiring off the inertia switch as the 12V+ trigger wire to energize the relay. So in my case the factory relay is still installed and I installed the second relay to increase the amps the pump could draw with a larger gauge wire from the battery to the relay and then to the pump.

Scrapla347 · Nov 5, 2025

AeroCoupe said:
Assuming you are no longer using the stock harness so put it where it makes sense. I put mine in the trunk as I used the factory wiring off the inertia switch as the 12V+ trigger wire to energize the relay. So in my case the factory relay is still installed and I installed the second relay to increase the amps the pump could draw with a larger gauge wire from the battery to the relay and then to the pump.

Terminator X is installed. I followed the instructions and connected the green trigger wire from the Terminator X to the pink wire under my driver seat at the stock fuel pump relay location but got no pump prime. I was told I would have to add a ground since the stock ECU was removed. I decided to instead run a thicker 10 gauge power wire and new relay for the pump. I was going to run the power to the back hatch area and splice into the pink power wire back there at the grommet. I was told that short run of smaller wire from hatch down to pump would be ok. It's a 255 in tank pump and I really don't want to drop my tank and wire directly into pump.

AeroCoupe · Nov 5, 2025

Just so you know (which you may already) but the stock ECU sends a ground to the relay to energize the coil.

Red/Black - 12V key on - Pin 85
Tan/Light Green - ECU controlled ground - Pin 86
Orange/Light Blue - 12V key on from fusible link - Pin 30
Pink/Black - Feed out to pump - Pin 87

If the Holley is sending 12V+ then you need to cut the red/black wire and connect that wire to the Holley wiring and reconnect the pink/black wire. This is if you do not want to mess with any of the stock wiring. I would suggest this.

Scrapla347 · Nov 5, 2025

AeroCoupe said:
Just so you know (which you may already) but the stock ECU sends a ground to the relay to energize the coil.

Red/Black - 12V key on - Pin 85
Tan/Light Green - ECU controlled ground - Pin 86
Orange/Light Blue - 12V key on from fusible link - Pin 30
Pink/Black - Feed out to pump - Pin 87

If the Holley is sending 12V+ then you need to cut the red/black wire and connect that wire to the Holley wiring and reconnect the pink/black wire. This is if you do not want to mess with any of the stock wiring. I would suggest this.

I removed my stock computer when I installed the Terminator X. It was suggested to me that I run a bigger power wire and new relay for the fuel pump and not use the green trigger wire to tap into the old wiring like the Holley instructions say to do. I was planning on triggering the green wire to the new relay, running the power wire to the rear and tapping into the pink and black power wire back there.

AeroCoupe · Nov 5, 2025

Then just completely remove all of the stock wiring out of the equation. If the holley uses 12V+ to trigger a fuel pump relay then you should wire is as follows:

30 - Battery power
85 - Holley green wire
86 - Ground
87 - Fuel pump power

If the holley uses ground to trigger a fuel pump relay then you should wire it as follows:

30 - Battery power
85 - You can jump this from 30 or use an ignition 12V+
86 - Holley green wire
87 - Fuel pump power

I would use a 10 ga wire from the battery to 30 on the relay and a 20 amp fuse. I would then run a 10 ga wire from 87 on the relay to the pump. This will provide up to 20A of power with no more than 3% loss in voltage.

Scrapla347 · Nov 5, 2025

I have 10 gauge wire with a 30 amp inline fuse to a 80 AMP relay. I got the 80 amp relay because they come with 10 gauge wires. The Holley trigger gives 12 volts so I was going to trigger the relay with it and run the power wire to the fuel pump power wire in the rear.

AeroCoupe · Nov 6, 2025

Punt the 80 amp relay as there is absolutely no need and it’s just one more thing that can fail.

Scrapla347 · Nov 8, 2025

I think I'm going to wire the green trigger wire from the Holley to my interia switch and see if I can just run the pump like that. I was told my 255 pump draws less than 15amps and the instructions say it's ok to use the green wire to run a pump as long as it doesn't exceed 15amps. I'm NA and running stock fuel pressure. The pump ran on factory wiring for years without any issues.

New fuel pump relay

Scrapla347

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AeroCoupe

lube between the nut and the face. I know my lubes

Scrapla347

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Scrapla347

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Sparky714

AeroCoupe

lube between the nut and the face. I know my lubes

Scrapla347

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AeroCoupe

lube between the nut and the face. I know my lubes

Scrapla347

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AeroCoupe

lube between the nut and the face. I know my lubes

Scrapla347

Active Member

AeroCoupe

lube between the nut and the face. I know my lubes

Scrapla347

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