I need a signal from the coil for a relay. Use the negative terminal, correct?
Yes, sorta…that is the trigger wire to fire the coil, so for each cylinder firing, there is a pulse. What relay do you want to energize?
I have a starter button connected to 87a so that when the engine is on the button is disabled. Is there another hot signal that is steady when the engine is running?
The fuel pump is only powered when the engine is rotating/running.
Doesn’t the FP fire for a couple seconds (3?) at KeyOn, then go off until engine turns? That might be splitting hairs, but who knows, maybe Brian’s application would be sensitive to that.
Great to see you Jim!
No. The fuel pump relay only closes when the DME sees timing data from a rotating engine.
I dunno. I accept that there is great risk disagreeing with such an experience person, but I’m pretty sure that I see my FP gauge pressurized when I go KeyOn. I also read somewhere that the purpose is to ensure that the fuel system is already pressurized when the starter starts turning. Sure, half of what one reads turns out to be wrong, but the FP gauge behavior does seem to confirm the idea.
If using an electronic gauge, it will show the residual rail pressure (assuming the check valve is working) when the gauge powers up. It is possible that this changed towards the end of E30 production, but my experience is that the pump doesn’t run briefly when the ignition is switched on. It is pretty easy to check with a test light.