Alternator Output Test

Fig. 1 Connecting Test Equipment for Output Test:

Use SUN VAT-40 or SUN VAT-60 or their equivalents for test.
1. Check system for loose or broken ground straps, loose or damaged V-belt, charging light operating properly and proper tightening of alternator.
2. Disconnect battery ground and positive cables.
3. Connect battery cutout switch to battery positive post, then the positive cable to battery cutout switch. Ensure battery cutout switch is in On position.
4. Connect ammeter, voltmeter and load resistance as shown in Fig 1. Ensure load resistance is connected to battery positive cable.
5. Connect battery ground cable, switch off all electrical accessories, then start engine and run at 3000 RPM.
6. Set load resistance so that ammeter shows approximately 20 amps, then turn battery cutout switch to Off position.
7. Adjust load resistance until ammeter reads 45 amps for 65 amp alternator or 50 amps for 75 amp alternator, then check that voltmeter reads between 12.5 and 14.5 volts.
8. If voltmeter reads between 12.5 and 14.5 volts, system is operating properly.
9. If voltmeter does not read between 12.5 and 14.5 volts, substitute a known good voltage regulator and repeat test.
10. If voltmeter reads between 12.5 and 14.5 volts, discard original regulator and replace with new part.
11. If voltmeter does not read between 12.5 and 14.5 volts, replace alternator.