Electric Fuel Pump Wiring

Hi, folks. I have recently picked up an '86 XJ6 with a 350 Chevy already installed – is apparently a first gen motor, probably something from the '70’s, and I believe I’ve got a Quadrajet on top of it. The car runs remarkably well, and the swap appears to have been done competently, but I live in Albuquerque, at one mile of altitude, and the swap was done in Seattle, at sea level. The car runs on the mechanical pump on the side of the motor but, surprise surprise, it’s already vapor locking and it was only 50 some-odd degrees out yesterday. I own several cars from the '50’s and they have all had vapor-lock issues when brought to this environment, and I’ve always resolved it by wiring in an in-line electric pump near the tank. The XJ6 obviously came with an electric pump in the trunk, but it would have been too much pressure for a carb and it was removed during the swap. I have found the white/green wire that powered it back there, but the wire is not hot under any circumstances – no power at the inertia switch, and when I went to check the fuel pump relay, it isn’t there. The only relay on the firewall is for the starter, with 3 empty prongs next to it. What I would like to do, ideally, is find a (ignition switch controlled) source of 12v power for the fuel pump from the front of the car and run it down the white/green wire to the trunk. However, I don’t see the wire at the firewall, and I’m not sure what power source I could use without stealing from something necessary with unintended consequences. So, 2 questions: 1) Does anyone have any suggestions of circuits I could tap into, possibly at the fuse panel(s), to use to power an aftermarket pump? 2) Does anyone have a good idea of where to look for the white/green wire near the front of the car? I’m guessing it’s in one of the harnesses, but not sure which one to check.

Thanks to all in advance, and I’ll try to update as I work. The game is afoot!

Welcome. Odd combination. An old tech carb in lie of EFI!!! Would be illegal here in nanny CA!!!

alas, the installer offed the fuel pumprelay that was on the fire wall adjacent to the starter relay.

  1. The + post on the coil is ignition on hot.

  2. Check the lid under the driver side scuttle. Fuse box and Id of the fuses. Vaguely recall that ignition on + is there.

  3. Were you so fortunate as to get the owner two manuals?

  4. Search the archives here for Jaguar Schematic S57. Excellent for workng on Jaguar electrics.

  5. I have mixed feelings on the “cold” inertia switch. Only needed because of the high psi of the EFI pump? My vote is to actrivate it if you have an electric pum, whatever the PSI!!!

I had a lot of “fun” with the electrics on my lump… LT1 power…


Thanks, Carl. I think the inertia switch is cold b/c the relay is missing, and would be upstream of it, right? However, thinking it through, I would just need to get power to the inertia switch, I think – it should be a straight shot from that to the pump.

I got a Haynes manual that doesn’t even have a S3 wiring diagram in it. Not much help there. I’ll look for S57. I checked the fuses on both sides of the cabin and neither mentioned fuel pump, so I was wondering if there was another circuit I could tap that wouldn’t object to the current the pump will want – given that I’m looking for 9 psi or less, I don’t believe the pump pulls very many amps.

This car becomes emissions-exempt on January 1st in my city and, hence, legal – which is why I bought it! Oddly, even if it had EFI, it still wouldn’t be legal – they won’t test cross-manufacturer swapped vehicles for emissions, and didn’t think my “but now it’s a hybrid” argument was as cute as I did.

As mentioned, the original fuel pump relay was centered on the firewall, next to the starter relay.

First, verify continuity through the inertia switch. Plan replacement if necessary (and temporarily bypass).

Use a test light and outside power source to see if the fuel pump wire has continuity all the way to where the relay was. If not, run a fresh wire (include the inertia switch).

Install fresh relay.

That should put sufficient power in the boot to run a proper fuel pump for your carburator engine.

Follow Carl’s advice and track down a copy of the S57 wiring manual for the XJ6 S3. I can not stress this enough.

thanks Bob. Nice to hear from you.

The one you made up for me years go has helped me resolve a bunch of issues.

Learned a lot as to auto circuitry in general .

Easiest schematic I have ever worked with.


Thanks for the reply. I’m working on tracking down a copy of s57, but have not yet found any reliable sources for one. Ebay lists nothing at this time, Jaguar Services seems to have vanished…

I do not have continuity from inertia switch to white/green wire in trunk, sadly. I do not find wires underhood near the firewall that might have gone to the relay, which was deleted. I really wish that the person who did the swap had done a little less tidying-up of deleted items, but gotta work with what’s there. The wiring diagram shows that power goes from the inertia switch to the tank selector switch before going back to the pump, but I doubt they pulled that switch or disconnected the wiring from those posts – and that switch is currently working, changing tank fuel is drawn from and corresponding sending unit, and I don’t really want to disturb it. Just from poking around some the other day I lost the right headlight and marker light (replaced fuse and they’re back, but now the right headlight comes on when the parking lights do, which I can live with) and the heater controls, which came back when I wiggled the fuse. I’m currently planning on tapping into the wire that heats my electric choke (it’s a thick wire, and only hot when ignition is on), running a thin wire all the way back into the trunk from that, and installing a relay back there to take advantage of the 12v hot at all time power that is supposed to work the radio antenna (leads to that motor are disconnected, probably for a reason!).

I think this is gonna be tough for people to help me with online at this point, as I’m so far from stock and am not the one who modified it, nor did I receive a diagram with it.


Okay, I found an '87-'88 s57 diagram online, and it appears to show a S3 car, not the next generation. So far things in the document seem to match up with what I’ve observed in the car, so I’m gonna roll off of this. Thanks again for the encouragement!

Great as to getting S57 guidance.

check along the right side of the console. And under the scuttle on that LHD passenger side. side. A thick bundle of wires should be there, unless it was 'cleaned" up by the PO. Many for the ECU and not needed. but, I recall the fuel pump wire is there!!!

And, gromett in the firewall where that bundle passes in to the engine bay. Just under the battery box.

Merry Christmas and Happy new year to all.


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Thank you, Carl. I’ve ordered the pump, will check the wiring again with additional resources now available this weekend!

Good call, Carl! I did find the large bundle of wires there, coming from the back, all of them cut and electrical taped together! Also found the white power wire in the bundle, so was able to send that through a relay and a switch and send power to the pump back along the white/green wire. Pump is in, working well and only on demand, which is how I prefer it (the mechanical pump can draw fuel through the electric pump, electric is there to pressurize the line when vapor lock begins).

Now on to my rear calipers, which are dragging!