Wild, Weird, Unexpected Electrical Problem/Solutio

I have a 1951 Allis Chalmers type B with which I have had a very puzzling electrical problem. I think I've solved it, but I wanted to add this experience to the knowledge bank at these archives.

For the record, I have a 12 volt system, alternator, ballast resistor and 6 volt coil.

The tractor was recently running really weak, then quit all together. I started tracing the problem back through the electrical system. No matter what I tried, I could not start the thing. I only ran the battery down from driving the starter. Then, I carefully pulled the cable off the coil to ensure I was getting a good spark there. I saw strong, inch-long sparks coming off the center lug of the coil - and suddenly, the tractor puffed to life! As long as I held the wire about an inch off of the coil, the tractor ran great! Too far, and the spark couldn't junp the gap and the tractor died. Too close or touching the coil - the tractor also died! I'm guessing that my voltage-dropping ballast resistor is bad (or poorly matched to the coil) and the removal of the cable from the coil provided the right amount of "resistance" via the gap jump to run the tractor at the appropriate spark voltage. Without the gap, the spark may have been arcing across the points, causing the real spark form the coil to the plugs to be weak.

Anyone else had this problem? I'm putting a new resistor on the tractor tomorrow - I'll report if that fixes the problem.

Andrew

Something in your ignition system is keeping your plugs from firing unless you apply an extra amount of voltage to them. Look at the above items and see if anything is amiss.

I didn't do this initially because I had just installed a set of CHAMPION plugs sometime last fall. Oh well, looks like a tune up to prevent refouling this set of plugs may very well be in my near future!

Thanks so much to all of you again.

Andrew

Thanks for the followup. Many times I sit and wonder if my advise was worth a hoot.