Hey guys my truck i thought ran out of gas but come to find out its losing power to the coil i can turn the key on with a meter on it power stays on for 1 second then goes away......what could cause this ......my truck is an 86 f 150 with a 300 6 cylinder......

 

Check each of the wires for continuity.

 

It will start when you crank it then it just dies out

 

Where does the power wire get its power from for the coil?

 

I'm having the same trouble with mine, suddenly one evening, it starts then when I let go of the key it dies. I've poked around with my test light quickly and can't find a problem.

I grabbed an old ignition module i had laying around, tried it, then the odd time it will start and run, but that's not good enough. So it may be the module that needs replacing.

Until I get another one shortly, this is what I did to get it running, since I need my truck daily.
1. Took the red wire (small one) off the solenoid, put it straight on the battery.
2. Ran a wire from the solenoid, into the cab.

Now when I want to start the truck, I put the key in RUN, grab the wire I ran into the cab, and touch it on a power source in the truck. (the back of my voltmeter that I have hanging down.) The battery does not get drained when the truck is off also.

Try this if you need to get it running temporarily.

 

brian.b,

Your 1986 4.9L originally came with the feedback [computer controlled] ignition. Is that still in place? If so, the computer can provide insight into what might be wrong.

 

Wiring does degrade over time and insulation fails. The engine compartment of our trucks is subject to the elements. ( Imagine yourself hanging on to a fender well under a hood going 70 mph down any of our great country's roads or highways). Road debris,salt,rocks and filth smacking you square in the face over and over again. After a while....you would look like Leatherface.
This goes for vacuum lines and hoses as well. Wiring as well as rubber does not last forever.