1150 Thunderbolt no spark

[Grinderguy]

I am working on my dad's 1977 thunderbolt 1150 which we just purchased used, which has no spark at the plugs (just an occasional random). The last owner broke the distributor cap and left it off, which corroded the rotor. I replaced both of these parts first before continuing on.

I have performed the switch box test and coil test, which I get a nice spark from the coil. Which I understand that proves the coil and switchbox are OK.

If I crank the motor over with the coil wire out of the distributor, I get a consistent 1" spark from the coil wire to ground.

The coil ohm-ed out correctly, as did the stator. I did find that the rectifier didn't pass all it testing, but my understanding that it is part of the charging system, and not part of the ignition system. I just ordered it before writing this.

I did purchase a used distributor off ebay, but unfortunately it was damaged in shipment. The seller is trying to resolve the issue with UPS, looks like UPS drove a fork from a forklift through the box.

Any suggestions in the motor diagnostics would be greatly appreciated?

 

[Chris1956]

Well, it sounds like it could be either bad spark plug wires, or perhaps the block is not well grounded. There should be 4 ground wires from the block to the lower cowling. The lower cowling has the ground wire bolted to it, so it is the source of ground. Make sure the block is grounded as well.
If that doesn't get it, maybe the new router or dist. cap is bad?

 

[Grinderguy]

Thanks Chris1956, Today,I spent a little time on the engine. Ohm-ed the stator again, checked the rectifier, retested the switch box spark/coil. Then all of a sudden, I had spark on the top cylinder, then the 2nd one down. Then I lost all spark again, or became just either when you start or stop cranking it. I agree, it is either a grounding issue, or a bad wire/connection somewhere.

 

[Grinderguy]

Today, I checked and cleaned the grounds. Replaced most of the wiring in the motor.

Then disconnected the throttle control box. Left only the battery positive battery connection and the ground to the motor. I placed a jumper between the two 12 vdc contectons on the switch box. Jumpering from the yellow wire, connection on the starter solenoid, and the positive, turned the motor over but no spark at the plugs or coil now.. I performed the switch box/coil which produced a spark at the coil. I put the crank to TDC, installed the coil wire performed the test again, which produces a spark at the #1 cylinder.

I think the trigger is faulty, but am questioning whether I am overlooking something or doing this incorrectly. Any suggestions?