Duster Wont Start

I used a voltmeter to test the charge of the battery, coil, and the ECU unit. Everything checked out except for the coil. I tested the charge on our Falcon, and the reading was 5.37 volts. On the Duster, the reading is -3.74 volts; is that my problem?

I am taking it to the parts house tonight to have it tested, in case I am doing it wrong. If they can't test it, I will replace it.

-- Drake