XJ6 S2 wire colour question

There’s a group of wires coming out of a central grommet at the rear of the boot area. None of them have been connected whilst I’ve had the car but there is a 15 amp brown wire with a purple tracer that has power all the time regardless of ignition…

In my colour code specs that is the colour for the alternator feed which doesn’t explain why it’s in the boot with constant power.

Anyone here have a clue as to what it’s there for?

Brown/purple comes from fuse #3 to power the boot light & switch…fuse # 3 is fed from the power post which the alternator happens to be connected to as well, the other wiring is most likely for trailer/caravan socket.

Goodo then, thanks… Hence power there all the time. If I want to use that wire to power a fuel pump on ignition/run is it just a matter of using a relay?

Thanks again. I just paid for a schematic.

power there all the time, it’s not connected to ignition on, you would have to divert the Brown/purple wire from fuse 3 to the ignition switch.

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If you want to run the car’s fuel pump with ign ‘on’, Don you do that by removing the fuel relay and short the white to white/green on the relay base…

However, this disables the fuel safety feature - so why would you do that? Not running the pump with ign ‘on’ and the engine not running/cranking is an intended feature…

xj6 85 Sov Europe (UK/NZ)

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As a caveman where auto electrics is concerned, I’m not sure I follow. Don’t I hear the pumps running/priming with ignition on? My application is for a high pressure 58psi pump for FI.

schematic sent…any question about wiring use the schematic email…tom

Pump is not meant to run with ign ‘on’, Don - unless the engine is running. As said, this is a design feature; priming is not necessary - the pump pressurize rail in ‘crank’…

To test functions; set gear lever to ‘D’ and turn to ‘crank’ - the engine should not crank, but you should hear the pump running. Second test; remove air filter and prop open the FM flap - the pump should then run with ign ‘on’.

As the engine draws air, the flap opens and a reed switch in the AFM activates the pump relay. The intent is to stop the fuel pump running if the engine stalls for some reason. It’s an accident response feature; if the driver cannot turn ign ‘off’ there is hazardous for the pump to run if the engine is not…:slight_smile:

There is no other factor involved in jumping the fuel relay as described…

xj6 85 Sov Europe (UK/NZ)

Okay, but on ignition it runs until primed then stops until car is started? But still it has power no?

what motor you have in that car, is it the later S2 efi or lumped engine?

The pump is powered through the relay, Don - the relay is activated either by ‘crank’ power from the starter relay, or power from the reed switch in the AFM. With relay inactivate there is no power to the pump. Basically, pump power through the relay is delivered by the white wire circuit - powered both with ign ‘on’ and in ‘crank’.

There is no separate priming function, but when ign is turned ‘off’, a one-way valve, between the pump and the fuel rail, retains pressure in the fuel rail. If it fails, or pressure drops over time, the pump will restore pressure within some 2 seconds while cranking…

Tom’s point is of course relevant, but all ‘our’ Jaguars’ fuel controls work the same way and on any engine, carbed or otherwise - unless a PO has modified it.

As an aside; you can only top up/‘prime’ fuel in carbs or rail by running the pump. In the old days you could prime the engine itself by pumping the gas pedal…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Thanks Frank, I understand now. There’s nothing wired up yet. I now think the solution is to just use the existing power architecture that is still there for the old pumps. I’ll leave it for someone else to take it to the next level. I really appreciate all the help.

Just add, Don, on carbed versions; instead of a plain relay a ‘fuel safety’ relay’ is fitted - incorporating the same features.

Here the engine state is detected by an oil pressure switch - standing, there is no oil pressure and in ‘run’ the relay is not grounded to energized it to run the pump. In ‘crank’, the relay is bypassed to run the pump from the ign key ‘crank’…

xj6 85 Sov Europe (UK/Z)