Troubleshooting Checklist: Alternators

Getting started
To begin, please review and complete the following steps. Do not charge the battery with a charger beforehand.

Step 1: In the engine compartment, locate the primary battery positive (+) and negative (-) posts. Be sure all the clamps are marine-grade. They should be soldered and sufficiently tightened.

Step 2: Locate the alternator positive (+) post. Be sure the output post nut is tight.

Step 3: Ensure that there is a heavy ground wire from the alternator mount to where the battery is grounded on the vehicle. If there is no such wire, install one using a 1/0 cable and be sure the output from the alternator to the battery is also a 1/0 cable. Other tips for ensuring a proper ground:

Do not ground the alternator to the engine. This is not sufficient.
Ensure there is no paint on the alternator mounting bracket (only applies to aftermarket bracket kits). Thick paint on the mounting bracket can cause an insufficient connection to ground the alternator.

Step 4: Loosen the alternator belt and turn the pulley. Confirm that pulley is not in contact with or rubbing the alternator frame. If the pulley is rubbing the frame, please contact us directly for assistance.

Step 5: Ensure that control wire plug is fully inserted into back of the alternator. These plugs are hard to insert.

Testing with your multimeter (VOM)

Test terminal

Test 1

Ignition off

Engine off

Test 2

Ignition on

Engine off

Test 3

Ignition on

Engine on – standard idle

No electrical loads

Test 4

Ignition on

Engine on – high idle

No electrical loads

Battery positive to negative

______ volts

volts s/b 12.6

If fewer volts, replace or charge battery.

If more volts, go to Test 2.

volts s/b 12.6

If fewer volts, replace or charge battery.

If more volts, go to Test 3.

volts s/b 13.8 - 14.9

If voltage is in range, unit is OK.

If fewer volts, go to Test 4.

volts s/b 13.8 - 14.9

If voltage is in range, unit is OK. Possible OE plug problem. Run Test 5 below.

If voltage is below range, alternator has no output. Repeat checklist steps 1-5 above.

Contact us
Still experiencing problems? Contact us for one-on-one assistance. International callers dial +1 (563) 323-7994, ext. 103. US callers dial (866) 466-8878, ext. 103. Normal business hours are 9 a.m.-4:30 p.m. CT Monday-Friday. Please be ready with your APS part and serial numbers, as well as vehicle and engine type, so that we may serve you better.