Coil testing 6 volt systems

[Guest F37Olds]

The coil on my 1937 Olds is 40 years old and I would like to make sure it's still in top working order before taking a long drive. Is there any way to check it out to be sure?

[Mark Shaw]

Checking Ignition Coil Polarity

You can test for correct polarity of the ignition coil by using a voltmeter. Connect the negative lead to the (-) negative terminal and the positive lead to the engine block.

Set the meter on the highest volt range (these connections are the same whether you have a positive ground or negative ground electrical system). The secondary winding's polarity, which you are testing, is determined by the combined hookup of the battery and primary windings.

Crank the engine over (do not start it) and the needle of the voltmeter should show an

upward swing to the plus or positive side (do not worry about taking a reading). If the needle swings down to the negative side and gives a negative reading, your coil is hooked up backwards. To correct the polarity, simply reverse coil primary leads.

A coil with reversed polarity will have about a twenty percent lower output which may not show up at idle and low rpms, but can cause an engine to miss or stumble under load and at higher engine rpms.

From: http://www.fifthaveinternetgarage.com/tech_tips/tech_tips_ign_coil_polarit.html

[Guest Albert]

There is no real way to test the coil of its currently working, kinda like a headlight in your car, it may last years, or days, maybe just keep a known good one in the trunk is the best insurance..or if the coil has LUCUS written on it, just replace it now, you never know when a cloud will pass over head...LOL

[Owen_Dyneto]

Albert's hit the target square on. Even the professional coil testers that were common in shops years back weren't very predictable in results. Generally, coils begin to show signs of failure first when they are hot; Adequate ignition with a cold engine and irregular ignition when the engine (and coil) are hot is a standard sign of coil failure.

[Bhigdog]

I see three options for your long trip.

1. replace the coil now and use the old one as a back up.

2. Take a new one along as a back up

3. Assuming the coil is a "generic" can type, don't worry about it, they are readily available enroute. Even if it is a special configuration type most likely you can Jerry rig one enroute if need be.......Bob

[Guest imported_49packard]

It is the high voltage side that usually gives out. It starts leaking to ground. Similiar problem I have had and I am having again is the high voltage connection from coil to distributor. This is the second time in about 2 yrs. The outside coating begins to crack and then starts breaking down.

[tbirdman]

I had a bad coil last year but it would only fail after driving for a while. Got towed three times in 2 weekends before I figured it out.

[Guest stude8]

I always carried a "Road Kit" with extra coil, points, condenser, fuel pump, water pump and belts. Never needed any of them, cheap insurance for a pleasant trip. The item you leave at home is what will most likely fail. Stude8