Ford Repair Questions? Ask a Mechanic for Answers ASAP
Let me see if I have it right: the engine will start and run; then stalls when the A/C or head lamps are turned on. Is that correct?
If yes, is your battery showing more than 13 volts at idle with no accessories on? Does voltage drop after 15 minutes?
OK. Let's not worry about voltage at the coil - if there is 14 volts at the positive side with the engine running, then we're good to go.
Let's put our attention on the battery. Does voltage go down once the A/C and the headlamps are turned on? Does it affect the brightness of the headlamps or the speed of the A/C blower?
The coil gets steady positive voltage from the ignition switch. Ground to it is applied intermittently by the onboard computer to match engine firing order - if you were to touch the coil negative terminal with a grounded LED test light, you would see it flash rapidly, similar to how the injectors are pulsed open.
Would it help you if I uploaded the factory wiring diagram?
Please do not ground the coil negative terminal. Doing so will burn the driver inside the onboard computer.
I'm sorry, but seeing that you disregarded my advice to leave the coil alone, I have no option but to opt out of this question. Please do not reply until another expert responds or the site will cycle it back to me.