1979 Mustang Constant 12V in Run and Start positions

[Skinney302]

Sorry if this has been answered, I've searched and can't find a solid answer on a source for constant 12V when my ignition switch is in the Start and Run positions. The issue is the 12v source required for the pink key on power wire used on a Holley Sniper setup. Right now I seem to get power as the pump cycles and I get the prime shot but the car wont seem to start unless I cycle the key multiple times (multiple prime shots) which I assume adds enough fuel to the intake for the engine to catch while cranking and when I release the key the ecu has power to continue running the engine and every thing runs smooth. I think my problem is that I'm using a switched 12V source that only supplies voltage in the Run position and I need it in both. I've looked at the wiring diagram in the old Haynes manual (yes, I'm that old) and one source seems to be the positive side of the coil, I'd be using it as a trigger for a relay. I've also read that that only provided 7-7.5 volts. Does anyone know if that's right? Thanks in advance for any help you can provide.

[at_the_junkyard]

Typically I believe the white/blue wire going to the original Duraspark ignition module is full 12V in run and crank position. The coil positive wire can have lower voltage when running if there is a ballast resistor in the circuit.

Assume your not using the old Duraspark box with your Sniper ?

[Skinney302]

For now I'm still using the duraspark, I didn't want to introduce an additional complication until I sorted the Sniper out. I'm looking for trigger voltage for a relay. I just tested the positive coil wire with a volt meter and it's under 5v in acc position and 12 volts when cranking. From what I've read 5v won't trigger the relay. I didn't want to run a toggle switch inside the car (which seems easiest) lol, so I may tap into the wire you suggested.

[at_the_junkyard]

Yep I used that wire for my EFI key on trigger on my 80 and it works. 5V in the accessory position or the ignition on position ? Typically the circuit provides 12V on the coil when starting and then switches through the ballast resistor when in run position to reduce the current. If you measure the coil positive when engine is running it should measure like 8 or 9V if there is a resistor. If not you should get full 12V running as well. The reduced voltage can only be measured properly when it’s running.

If your using the white wire with a relay then should be all good. At some point you will probably want to hook up your sniper to control the spark if it has that function. Those systems are supposed to work better if it controls fuel and spark together but you don’t have to.

[massacre]

I use the white/blue wire for my Term X relay.

[Skinney302]

Thanks for all the help!!! I started rewiring it last night and I'll let you know how I make out