Coil test

[Curti]

Is it possible to bench test a standard 6V Auto - Lite coil?

[Joseph P. Indusi]

You can test the primary winding (low voltage or battery voltage) with a digital ohmeter. A good coil should read only a few ohms. The secondary winding from the coil high voltage tower to one of the primary terminals shoudl test in the thousands of ohms. If you get an open circuit or infinite ohms on either, then the coil is defective. However, if you get some resistance reading with the digital ohmeter, the coil still could have shorted turns and this is more difficult to test for. Here you would have to rig up a battery to power the primary and a method to check for high voltage at the secondary when you interrupt the primary voltage. There are also coil testers but these are not common. Best method is to substitute a known good coil in the car.

Joe, BCA 33493

[Rusty_OToole]

Resistance values should be in the car maker's repair manual if you know what car it came off of.

[Curti]

The reason I pose the question is I just purchased a really cool 1935 Auburn sedan survivor. A few items under the hood have been replaced with non original items the coil being one. While at Hershey I found a correct AutoLite coil with just the right patina. I did the test. When measured across + to - it tested 1.3 ohlms and the tower to either + or - 3049 K ohlms. A new 6V A-L coil measures 1.3 & 2921. From this test, I suspect the coil is OK. I am aware of coil failure when they are heated up. Thanks for the help.

[Pete K.]

When it comes to old coils and old cars, I try and use correct, original coils but I expect any one of them could fail on the road, so carry a known good one under the seat. I have an 87 year old coil in my Dodge, still going strong--but for how long? Perhaps longer than I.