Try the same test but move the ground to the engine. The other question is why you do not have full battery voltage at the trucks normal wire connected to the coil positive. Are you getting battery voltage at the ASD relays points both in and out?

 

Yeah I have good connection from relay, I double checked that. I did this test with an extra battery but ill try it with the trucks battery tomorrow. I just thought the coil would put out more than that but as long as it has an arc its good to go right?

 

An extremely poor spark may be OK out in the open but not run the engine because that spark is not strong enough to jump the plug gap under cylinder pressure. I do know that under test conditions you loose the electrical inertia that helps a coil produce a good spark. I can't tell the quality of spark you are getting but if you can get a spark in the truck you can trouble shoot by changing one thing at a time until you find when you lose that spark and that should point you to the problem.

You say you checked the ASD relays connection. Does that mean you now have battery voltage at the coils + wire in the truck when the key is on? If not you must solve that problem.

When you test the coil in the truck first use power and ground directly to the battery, then switch to the engine ground, and then switch to the trucks power wire to the coil.

Maybe reading this will help you understand how and why a coil works the way it does. I have never figured out what takes the place of the very important purpose the capacitor plays in all of this when they went away from points to electronic ignition but something has.

http://mgaguru.com/mgtech/ignition/ig108.htm

Here is a video that might help you know what kind of a spark you can expect to see since I can't judge the spark you are getting.

http://www.youtube.com/watch?v=rJYJ3KvPhhY

 

Thanks for that. It makes more sence now. Ok I don't have that kind of spark, so by reading on I'm pretty sure that on this electrical system the control module has the actual capacitor internally. The wire on the negative side is routed from the coil to the module through an internal capacitor of some sort then out to the distributor where it breaks connection at the proper time. Guess that's y I wasn't getting a good spark when just hooking it up to the battery...I didn't have anything to store energy for the coil to release. Or something like that? Maybe? Lol

 

I'm having same problem with my 90 model 150 PU,
The thread ends with him never saying if the problem was resolved .
wondering if we could find more info on the outcome and isolate the problem?