16 To check the electrolysis, we connected the voltmeters negative connection directly to the battery. It only takes a few minutes to test and can save the engine and radiator. Remember to check the ground strap from the engine to the frame if the volt reading is higher than .5 volts A/C or D/C. The voltage should be checked while the engine is started. Starters produce high currents, and although it's for a very short burst of electrical energy, it can be very damaging long term.