I’m about to wire a kill switch to the fuel pump relay and am trying to find out which wire I need to splice the switch into. The red and white wire is the only one which is live when the ignition is turned on so I presume that it is that one.
Which wire do I need to cut?
Roadster Robbie states that this is the main relay. The blue/red one supplies the fuel pump but the voltage on this does not change when I turn the ignition on.
Do you have the relay fitted when you measured the red/blue
I expect that this would only come live with the relay fitted, as the feed would come through the relay first.
I have never removed the relay. I’ve just followed this guide on Youtube.
https://www.youtube.com/watch?v=XUhXLsrZiE0
I admit that while I can solder okay, electronics have never been my strong point.
that’s not you holding the yellow connector then ?
Yeah that me. Told you I wasn’t great with electronics.
Edit: so the plug is the relay itself?
It’s a good question!
Fuel pump would not use much power. Relay is in place for dual switching rather than circuit/switch protection, so my theory is put the switch directly onto the fuel pump supply wire.
The yellow plug is not the relay, that’s just a connector the relay would have been connected to it.
something like this
https://static.cargurus.com/images/site/2015/05/30/11/05/pic-5725464818837092050-1600x1200.jpeg
Without me seeing a wiring diagram, and only going on the info you posted earlier.
The white/red will feed in to the relay, when the relay is energised, this will provide power down the blue/red to power the fuel pump.
If you pulled the plug off the relay, then there will be no power going down the blue/red.
I’d say that you could put a switch in between white/red, blue/red and the plain black, which is the one I’d opt for personally.
I assume the requirement is to insert a kill switch in the circuit to act as an immobiliser. On that basis cutting in to one of the wires associated with the connector seems like a perfectly reasonable idea.
It works as a cheap imobilsor, and if the switch is well hidden, then a pretty good one at that.
I did this many years ago on a number of Ford Injections (XR’s, RS Turbo etc)
The car will start initially, but cut out within a few seconds.
When I go on holiday, I’ll generally pull the fuel pump fuse out.
Decision time then, white/red or blue/red?
I went for the Blue/Red in the end and it seems to work well.
