So I let someone borrow the truck... once they were 300 miles away...
"It died 10 times while driving 3 miles, restarted every time, so I just parked it. When it restarted, it backfired."

I switched out the ignition module, the coil, and the pickup. I'm getting power at the positive terminal, and the negative terminal when starting at the coil. The center pin on the distributor cap also has power. (I only had a test light with me...).

I tested for no spark by pulling out two different plugs and setting them on the master cylinder.

I love this truck-- we've been stuck in the woods more times than I can count, but it was always a simple "stuck in the mud" and I fixed it with a little elbow grease and a come-along. Any ideas would be very appreciated!

 

Take your testlight and clip the wire on a good ground on the engine, and then probe the negative terminal of the coil while someone cranks the engine. The light should blink. If it doesn't blink, the coil is not be turned on and off, so it will not make spark. What turns the coil on and off? The ignition module. What tells the module to turn it on and off? The pickup inside the dist. Make sure the dist rotor is turning when the engine is cranked.

 

The rotor is turning...

So I should assume that one of the three parts I replaced is bad? I won't be able to test the truck until next weekend when I can drive up there again.

 

People have had problems with corrosion in the plugs going to and from the distributor.

 

Are those the spark plug wires, or that wiring harness that goes to the pickup? That thing was so covered in grime, and the plastic so brittle that it was a real pain to get out, but I felt like the connections were decent.

Thanks for all your help!

 

Plugs between the dist and the module.

 

This plug comes out of the distributor and has orange, black and purple wires.

 

Would it be a bad idea to just splice the wires together, and cover them liberally with some electrical tape? If so, why?

Thanks for helping me out! I was ready to call the Ford Dealership and pay half what the truck is worth to fix it...

 

I don't think it is a good idea to try and eliminate the connector.

You should pull the plugs apart and check for corrosion.
If it is all green and scaly in there try cleaning the pins with a scotchbrite pad or something similar.
Spray the gook out of both sides with electrical contact cleaner.
Work the plug in and out to try and rub off more of the corrosion.
Spray it out with contact cleaner again.
Fill the contacts with dielectric silicone paste so it doesn't happen again.

The backfire is a classic symptom of the DuraSpark II module going bad.

If it backfired through the carb (and you still have the stock 4180 carb)
Then you definitely blew out the PowerValve.
You need to replace it or the truck will run VERY rich, if at all.

 

If you do as suggested by Jim, be sure to use electrical contact cleaner that's safe for plastics.

I agree with Jim, spliced connections held together with electrical tape are never a good idea, even more so when they're exposed to the extremes of an under-hood compartment.

 

replaced rotor cap and rotor. Still no spark. The coil negative seems to stay full on. Ideas? I cleaned the electrical connection to pickup and the two to the ignition module. Any others I should clean?

 

I'm far better on mechanical issues than electrical but....... I had ongoing trouble with the connector at the distributor - it looked clean but I finally cut it out in frustration & soldered the wiring - end of problem, in my case.

 

You changed the module, the coil and the pickup.
There's not much else except the harness between those components.

You might have a look at this; Duraspark - Troubleshooting - BumpWiki

 

Well, the mechanic switched out the ignition module, and got a spark. Guess I just got a bad part. Thanks for all the help.