How to Make a High Tension Coil Tester

Recharging magnetos with an inexpensive homemade high tension coil tester

| May/June 1989

Many newcomers working with magnetos are stumped when it comes to coil testing. An automotive oscilloscope has a coil and a condenser tester on it that may be used toas a coil tester for a magneto. Coil testers are available on the market, but they are either scarce or very expensive. There is an alternative for that "just once in awhile" coil tester. Please note that this information is intended for the novice and not an experienced magneto repairman.

A very effective coil tester may be constructed with a conventional contact point type automotive distributor. Any distributor from any car would serve the purpose, as long as it had a serviceable contact set and condenser. You would have to check to see that the contact points were opening about 0.018 inch. The other items needed would be:

1) Three pieces of test leads made up of approximately 18 inches of 14 gauge wire with battery clips on both ends. Alligator clips would be suitable.

2) One foot of 7mm spark plug cable (use metal core, not TVRS cable), with alligator clips on one end and spark plug wire terminal on the other end.

3) A test spark plug, available at most automotive parts stores with a battery type clip attached. This provides a test gap of 1/4", that is 0.250 inch (high voltage spark tester).

4) A six volt dry cell battery available at any parts, hardware, or department store. The dry cell is much more convenient to use than a wet-type battery.