Ballast resistor failure?

[Bruce B.]

What is or are the common causes of ballast resistor failure.

Possibly wire breakage due to the heating and cooling cycles or vibration?

[Timothy B.]

Re: Ballast resistor failure?

Bruce, You probably answered your oun question.. I guess one other cause could be excess voltage.

[Jack H.]

Re: Ballast resistor failure?

I can add other cause factors... There were two versions of the ballast ceramic (early/late) with the change taking place approximately 1958.

The early version had a 'trough' in the top side of the ceramic that extended from the wiring contact posts inward but not outward (toward the outer ends of the ceramic). The later version extended the 'trough' all the way across the ceramic from the outside ends, through the contact post area and inward. This was a design improvement.

The early version used a threaded insert to physically attach the resistor's winding wire to the contact posts. The insert has a physical crimp tab on it that's bent down into the 'trough' to prevent the insert from spinning when you torque the screw(s) that bind the engine harness wires to the ballast.

Should you over-torque and break the crimp, the insert will 'free wheel' and you won't get sufficient contact compression for good electrical connection. Expect the contact surfaces to oxidize over time with resistance building and excess heat generating OR the contact surfaces to climb SO HIGH in resistance that there's insufficient current flow through the ignition primary circuit.

The later design used the full length 'trough' in the ceramic to support two opposing crimp tabs on the insert. So, you gained anti-spin redundancy as well as more strength to support contact post to electrical connector torque down.

In either case, a ballast that's aged, has oxidation build up on the various contact post components AND if it isn't sufficently torqued can grow further oxidation and behave erratically, especially if it's left to sit for long periods of disuse...