Fifth Avenue Internet Garage

Tech Tip Archives

Just like with anything...if you spend enough time doing it you tend to get good at it, and you learn a few shortcuts to make your life easier. Having spent twenty plus years solving electrical, cooling, and fuel related problems on all types of antique and classic vehicles, I have "earned" a few tech tips that I want to share with you. Check back often, as I will keep adding to the list as time allows. For more tech tips, check out the Tech Tip Archives.

Randy

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 volt meter 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.