Hello fellow Jaguar XJS lovers! I have a 94 XJS and it conked out back in May. I have spent the summer tinkering around with it and have put on a host of new sensors, engine components and so one. The most recent was the Crank position sensor. Still won't start. I replaced the fuel pump as well. It doesn't seem to be working so I have the back brace off thinking that MAYBE in my genius I left the fuel pump unplugged. HOWEVER, what I have found in checking for power is that my light comes on in both the power wire and the ground. I know that there should not be power coming from the ground side. The Alldata diagrams show the ground wire as attaching to the body somewhere. Where could this power be coming from???

Thanks,

Tony in NM

 

Please excuse me if you already know this, but as it is a circuit, the current is flowing from the live wire, through the pump, and into the earth wire. Therefore, if the circuit is live, the earth wire will be carrying current which will be on its way back to the battery via the chassis. The only odd thing would be if, repeat if, the earth wire is NOT connected to the pump and it is carrying current - but that would be expected to fry the wiring in seconds.
Think of a light switch, current goes to the switch, but not out of it unless the switch is closed, in which case the entire circuit is carrying current.

 

Greg is correct, of course, in that a ground circuit/ground wire is 'live' because it carries current just like a "+" voltage supply wire...which some call a "hot wire".

If you mean that both wires show "+" voltage then, yes, the pump can't operate.

Just to clarify, are you using an ordinary simple test light with a probe on one side and wire with an alligator clip on the other? If so, with the clip attached to the battery "-" post, the light with glow only if you probe 12 volt "+".

With the alligator clip attached to the battery "+" post, the light will glow only if you probe a ground/earth.

If you had 12 volt "+" on a wire that is attached to a body/chassis ground....you'd have smoke and melted wires

Can you post the diagram you are using and/or describe the test method you are using?

Cheers
DD

 

Do you have voltage on the ground wire with everything connected or did you disconnect the ground wire, THIS IS IMPORTANT. because if everything was connected then you have a break in the ground connection.

If everything was connected then disconnect the plug from the pump and check continuity to ground, it must be less than 1ohm.

 

Sorry guys, but I figured it out and feel stupid about it. I thought I was using a test light, but as it turned out had a continuity light. Once I realized that, everything was ok.

Tony

 

Maybe you have a rare positive earth conversion