Component Tests and General Diagnostics

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

Alternator output test

- connect alternator/regulator tester according to manufacturer's instructions
- start engine and run at 3,000 rpm
all electrical accessories must be OFF

- adjust load to maximum ammeter reading
do not allow voltage to go below 12 volts
maximum ammeter reading should be at least alternator rated output minus 16 amps
if ammeter reading is more than 16 amps below alternator rating, replace regulator and retest
if ammeter reading is still too low, alternator is defective

Regulator test

tester still connected
all electrical components OFF and NO ammeter load

- run engine at 3,000 rpm until voltage stops rising
voltage should be 13.5 - 14.5 volts

if NO, replace regulator and retest

Diode test

tester still connected

- run engine at 3,000 rpm
- adjust load according to manufacturer's instructions
if meter reads "bad," replace alternator

CAUTION: Never run alternator with battery disconnected

Current drain test

- turn OFF ignition switch, radio, and all lights
- leave rear window defogger switch and air conditioning switches ON to check air conditioner relay and load reduction relay
- disconnect ground cable from battery
- connect test light between ground cable and negative battery terminal
if test light burns brightly, something is switched ON or shorted and draining battery

- remove fuses from fuse/relay panel one at a time until test light goes out to help locate problem
if no faults are found in fused circuits, disconnect cables from non-fused components, i.e. alternator, starter motor, ignition system and dashboard instruments until test light goes out

Alternator charging light test

Note: If battery is still not being charged, even though charging light operates properly, check alternator charging light circuit

- disconnect battery ground strap






- remove instrument cluster
- attach multimeter US 1119 between contacts 9 and 13 on printed circuit board
specification: 140 - 160 ohms

If value is greater than 160 ohms:
- replace printed circuit board