I have to do a number of should-be running tests on a non running 1992 XJS V12. My ancient MG has a little button under the hood to let you spin the starter from under the hood while testing something else. It is super handy! So I want to wire a momentary switch into the starter relay… but it has a weird diode in the wiring diagram. Is it safe to jump the starter relay without that diode? I’ve included a wiring diagram:
The diode is to stop arcing across the starter contacts in the ignition
switch.
You can easily apply +12V to the positive end of the starter relay coil.
Why not break that WY wire and put in a small 2 circuit terminal block with
a link so any time you can connect up a switch to turn on the coil.
Richard Dowling, Melbourne, Australia. 1979 coupe + HE V12 + manual; 1989
convertible; 2003 XJ350.
Piece of cake, John. When I first got my car the ignition switch was unreliable, so I wired up TWO push-button switches under the hood- one bypasses the ignition switch, and the other (heavier) switch and wiring bypasses the ignition switch AND starter relay. Since then I overhauled the ignition switch and put a push-button switch below it . Overkill I know, but my car ALWAYS cranks over, one way or another!
Easy. In a way, yes. But, caveat. The diode. I barely get it, if at all., Richard has one idea and he may well be right.
In my recent starter travails, I used such a device. Much cruder, but effective. A “red” wire at the starter solenoid going up in to the engine bay. The other bare, but covered with a wisp of tape.
To crank, jut touch it to battery +. Caveat. shifter in Park!!!
The neutral start feature is bypassed!!!
Carl