Alternator Repair + Checking Information

Alternator, repairing (55 A, 65 A, 90 A, Bosche type) Checking alternator and voltage regulator with battery cutout switch and load resistance-Page 27.12

Troublechooting-Page 27.14
CAUTION

Never run alternator with battery disconnected


Alternator/regulator, checking (with Sun VAT-40 or equivalent)

Visual checks

- check for:
^ loose or broken ground straps
^ loose or damaged V-belt
^ properly operating alternator charging light
^ proper tightening of alternator



Work sequence

- disconnect battery ground strap
- disconnect battery positive cable
- connect battery cutout switch to battery positive pole
- connect positive terminal to battery cutout switch

Be sure battery cutout switch is in ON position



A - Ammeter
V - Voltmeter
Ohms -load resistance
a - to starter
b - to fuse box terminal 30
X - battery cutout switch (SUN electric or

equivalent)

- connect ammeter, voltmeter and load resistance as shown. Be sure load resistance is connected to battery positive terminal
- connect battery ground strap
- start engine and run at 3000 rpm
- set load resistance so that ammeter shows approx. 20 amps



- turn battery cutout switch to OFF position
- adjust load resistance until ammeter shows
^ 35 amps for a 55 amp alternator 45 amps for a 65 amp alternator 60 amps for a 90 amp alternator
- check that voltmeter reads between 12.5 and 14.5 volts

If yes: system OK
If no: substitute known good voltage regulator and repeat test. Check that voltmeter reads between 12.5 and 14.5 volts
If yes: discard original regulator and replace with new part
If no: alternator is bad. Check individual parts and replace if necessary.