Ignition Coil Wiring

[jjred1977]

Hello,

I have a 1988 Ford Ranger 2.0L that I've had to rewire after a mouse got into the engine compartment, chewed through the alternator harness and caused a fire. The problem I'm having is the coil is overheating. I've already toasted one coil and do not wish to burn up another. The new coil that I'm going to put is a STANDARD MOTOR PRODUCTS FD476. The parts description says it does not have an internal resistor nor is an external resistor required. I have checked the wiring diagram for this truck and there is supposed to be a 1.0 resistance wire somewhere in the harness.

My question is how do I check to see if this wire is there and connected? Also, how do I know for sure that the coil is wired correctly and receiving the correct current?

The truck ran fine for two or three minutes after I got it running again until it just died and I noticed the coil was super hot. I had the ignition module tested and it is working. I'm using a Painless Wiring harness part number 30812. Their technical assistance is terrible and their instructions for wiring their harness is vague at best. I got the truck's ignition system running this far without their help. Any help with the coil problem would be very much appreciated.

Thanks

James

 

[RonD]

On the older coils there was a two wire power system.

There would be a 12v wire from the starter solenoid running to the + terminal on the coil.
This wire would either be on its own terminal on the solenoid(4 post solenoid), labelled "I", or it would be on the starter motor side terminal(3 post solenoid).
This would give the coil 12v only when starting(when engine was cranking).
If this wire is there make sure it is on the starter motor side of the solenoid, or coil will be getting 12v 24/7.
If this is the only wire going to the + terminal on the coil and you move it to the starter motor side, engine will fire when cranking but will die when starter motor is no longer cranking, that's when the "second" wire takes over.

The second wire is connected to the + terminal on the coil as well, it comes from the key switch and has voltage when key is in the RUN position.
It would either have a ballast resistor or resistor wire in between the key switch and coil.
This would give the coil 7v-9v when engine was running, still good spark but coil wouldn't get as hot.
You could check for this wire with a volt meter, it will have less voltage, like 8volts, instead of 12v.
Or you can add your own ballast resistor and new wire.

One thing to also check is your charging system.
A battery should have 12.5-12.8v with engine off
With engine at idle 13.6-13.9v, it can go as high as 14.8v just after starting the engine but should come back down to below 14v in a few minutes.
If it's staying up high then coil will be getting whatever that voltage is so will heat up pretty darn quick.
It will also limit the life of your battery.

 

[jjred1977]

Thanks RonD,

I will check for the resistance wire sometime this week if I have time but it may be this weekend before I can get to it.

I probably toasted the coil by accident because I hooked the red wire of the Painless harness directly to the battery to see if it would start (it did and ran for awhile). I assume the coil got full alternator voltage and caused the coil to finally die after 2 to 3 minutes of this abuse.

Where should the red wire be connected. I know a 12v source but where would be the best place to connect it? Would the ignition switch wiring be the best place? If so, which wire should I connect it to?

I'm not an electrician and I've gotten this far by getting generous help from people like you.

Thanks,

James