Section 14-00: Battery and Charging System—Service
1994 Mustang Workshop Manual
DIAGNOSIS AND TESTING

Pinpoint Tests

  

PINPOINT TEST A: SYSTEM OVERCHARGES (BATTERY BOILS OVER)

 

A1 CHECK VOLTAGE DROP IN 'A' CIRCUIT

Yes
GO to A2.

No
SERVICE excess voltage drop in Circuit 36 (Y/W). CHECK fuse and connectors in Circuit 36 and SERVICE as required.

 

A2 CHECK VOLTAGE DROP IN 'I' CIRCUIT

Yes
GO to A3.

No
SERVICE high resistance in Circuit 904 (LG/R).

 

A3 CHECK FOR POOR GROUNDS

  • Check for poor ground connections between generator regulator and generator , generator and engine, or engine and battery .
  • Are all ground connections clean and tight?
Yes
GO to A4.

No
CLEAN or SERVICE grounds as required.

 

A4 CHECK FOR FIELD CIRCUIT DRAIN

  • Turn ignition switch to OFF position.
  • Measure voltage at test point 'F' on the generator regulator .
  • Is voltage at test point 'F' equal to battery voltage?
Yes
Generator is OK. REPLACE generator regulator .

No
GO to A5.

 

A5 CHECK FOR GROUNDED SLIP RING

  • Remove generator from vehicle.
  • Remove generator regulator .
  • Measure resistance from each generator slip ring to the generator housing.
  • Is resistance from either slip ring to housing less than 200 ohms?
Yes
If grease or dirt has accumulated near the slip rings, CLEAN the slip rings and RECHECK resistance. If still less than 200 ohms, REPLACE generator .

No
REPLACE generator regulator .

  

PINPOINT TEST B: INDICATOR LAMP STAYS ON, ENGINE RUNNING

 

B1 CHECK FOR OPEN 'A' CIRCUIT

  • Measure voltage at test point 'A' on the generator regulator .
  • Is voltage at test point 'A' equal to battery voltage?
Yes
GO to B2.

No
CHECK fuse in Circuit 36 and REPLACE if required. If OK, SERVICE open in Circuit 36 (Y/W).

 

B2 CHECK FOR SHORTED 'I' CIRCUIT

  • Remove three-pin generator regulator connector.
  • Turn ignition switch to RUN position.
  • Is indicator lamp on?
Yes
SERVICE short to ground in Circuit 904 (LG/R).

No
GO to B3.

 

B3 CHECK 'S' CIRCUIT FUNCTION

  • Install generator regulator connector.
  • Remove one-pin 'S' connector.
  • Connect wiring harness 'S' terminal, Circuit 4 (W/BK) to the positive (+) battery post using a jumper wire.
  • Is indicator lamp on?
Yes
REMOVE jumper wire. GO to B4.

No
REMOVE jumper wire. GO to B5.

 

B4 CHECK FOR OPEN 'S' CIRCUIT

  • Remove three-pin generator regulator connector.
  • Measure wiring resistance between the one-pin 'S' connector and the 'S' (center) pin of the generator regulator connector.
  • Is resistance greater than 1 ohm?
Yes
SERVICE open or excess resistance in Circuit 4 (W/BK).

No
CHECK for loose or bent pin in generator regulator or connector. If OK, REPLACE generator regulator .

 

B5 CHECK STATOR OUTPUT VOLTAGE

  • Start engine.
  • Measure voltage at the 'S' terminal on the back of the generator .
  • Is voltage at least 1/2 of battery voltage?
Yes
GO to B6.

No
GO to Pinpoint Test H to find the cause of low generator output.

 

B6 CHECK GENERATOR OUTPUT VOLTAGE

  • Measure voltage at the B+ terminal on the back of the generator with the engine running at 2000 rpm and all accessories turned OFF.
  • Is voltage greater than 15.5 V?
Yes
GO to Pinpoint Test A to find the cause of high output voltage.

No
REPLACE generator regulator .

  

PINPOINT TEST C: INDICATOR LAMP STAYS ON, IGNITION SWITCH OFF

 

C1 CHECK LAMP CIRCUIT WIRING

  • Turn ignition switch to OFF position.
  • Remove three-pin generator regulator connector.
  • Measure voltage at wiring harness 'I' terminal, Circuit 904 (LG/R).
  • Is voltage greater than 0 V?
Yes
SERVICE Circuit 16 (R/LG). Circuit should be hot in RUN position only.

No
SERVICE instrument cluster. REFER to Section 13-01.

  

PINPOINT TEST D: INDICATOR LAMP DOES NOT COME ON

 

D1 CHECK FOR OPEN 'I' CIRCUIT

  • Remove three-pin generator regulator connector.
  • Turn ignition switch to RUN position.
  • Measure voltage at wiring harness 'I' terminal, Circuit 904 (LG/R).
  • Is voltage greater than 0 V?
Yes
GO to D2.

No
SERVICE open in Circuit 904 (LG/R).

 

D2 CHECK FOR BURNED OUT BULB

  • Connect wiring harness 'I' terminal, Circuit 904 (LG/R) to ground with a jumper wire.
  • Is indicator lamp on?
Yes
REMOVE jumper wire. GO to D3.

No
REPLACE lamp or SERVICE high resistance in lamp socket or Circuit 904 (LG/R).

 

D3 CHECK FOR POOR GROUNDS

  • Check for poor ground connections between generator regulator and generator , generator and engine, or engine and battery .
  • Are all ground connections clean and tight?
Yes
GO to D4.

No
CLEAN or SERVICE grounds as required.

 

D4 CHECK 'S' CIRCUIT WIRING

  • Remove one-pin 'S' connector from generator .
  • Measure voltage at wiring harness 'S' terminal, Circuit 4 (W/BK).
  • Is voltage greater than 0 V?
Yes
SERVICE Circuit 4 (W/BK). Circuit should be "HOT" only when engine is running. CHECK for swapped wires in generator regulator connector.

No
GO to D5.

 

D5 CHECK FOR SHORTED RECTIFIER

  • Measure voltage at the 'S' terminal on the back of the generator .
  • Is voltage greater than 1 V?
Yes
If lamp is on with one-pin 'S' connector removed, REPLACE generator .

No
REPLACE generator regulator .

  

PINPOINT TEST E: INDICATOR LAMP FLICKERS/INTERMITTENT

 

E1 CHECK FOR LOOSE CONNECTIONS

  • Check these connections for corrosion, loose or bent pins, or loose eyelets:
    • Three-pin generator regulator connector.
    • One-pin 'S' connector.
    • Generator 'B+' eyelet.
    • Power distribution box eyelets.
    • Battery cables.
  • Are all connections clean and tight?
Yes
GO to E2.

No
CLEAN or SERVICE connections as required.

 

E2 CHECK FOR FIELD CIRCUIT DRAIN

  • Turn ignition switch to OFF position.
  • Measure voltage at test point 'F' on the generator regulator .
  • Is voltage at test point 'F' equal to battery voltage?
Yes
GO to E3.

No
GO to E5.

 

E3 CHECK FOR LOOSE 'A' CIRCUIT FUSE

  • Start engine.
  • Check the generator fuse in the power distribution box for a loose connection by wiggling the fuse with the engine running.
  • Does indicator lamp flicker?
Yes
SERVICE loose fuse connection.

No
GO to E4.

 

E4 CHECK 'A' CIRCUIT CONNECTIONS

  • With engine running, connect test point 'A' on the generator regulator to the positive (+) battery post using a jumper wire.
  • Does indicator lamp flicker?
Yes
REPLACE generator regulator . If concern still exists, REPLACE generator .

No
SERVICE poor connection in Circuit 36 (Y/W).

 

E5 CHECK BRUSH HOLDER SCREWS

  • Remove generator from vehicle.
  • Check the brush holder screws, located on the generator regulator (test points 'F' and 'A').
  • Are the brush holder screws tight?
Yes
GO to E6.

No
TIGHTEN screws to 2.8-4.0 Nm (25-35 lb-in).

 

E6 CHECK FOR GROUNDED SLIP RING

  • Remove generator regulator .
  • Measure resistance from each generator slip ring to the generator housing.
  • Is resistance from either slip ring to housing less than 200 ohms?
Yes
If grease or dirt has accumulated near the slip rings, CLEAN the slip rings and RECHECK resistance. If still less than 200 ohms, REPLACE generator .

No
REPLACE generator regulator .

  

PINPOINT TEST F: GENERATOR NOISY

 

F1 CHECK FOR ACCESSORY DRIVE NOISE

  • Check the drive belt to make sure that it is installed properly and is not damaged. Refer to Section 03-05.
  • Check the accessory mounting brackets for loose bolts or misalignment condition.
  • Check for a bent pulley.
  • Is accessory drive OK?
Yes
GO to F2.

No
GO to Section 03-05 and SERVICE accessory drive as required.

 

F2 SUBSTITUTE KNOWN GOOD GENERATOR

  • Remove generator and replace with a known good generator .
  • Is noise present with a known good generator ?
Yes
Generator is OK. INSTALL original generator . CHECK other accessories to find the cause of the noise.

No
REPLACE generator .

  

PINPOINT TEST G: RADIO INTERFERENCE

 

G1 VERIFY RADIO INTERFERENCE

  • Start engine.
  • Tune radio to a station where interference is present.
  • Remove three-pin generator regulator connector.
  • Is interference present with connector removed?
Yes
Generator is OK. REFER to Section 15-00 to find the cause of the radio interference.

No
GO to G2.

 

G2 SUBSTITUTE KNOWN GOOD GENERATOR

  • Remove generator and replace with a known good generator .
  • Is interference present with known good generator ?
Yes
Generator is OK. REFER to Section 15-00 to find the cause of the radio interference.

No
REPLACE generator .

  

PINPOINT TEST H: BATTERY DOES NOT HOLD A CHARGE

 

H1 CHECK FOR KEY-OFF DRAIN

  • Turn ignition switch to OFF position.
  • Turn off all lamps and accessories and close doors.
  • Connect an ammeter or test lamp between the battery ground (-) cable and the negative battery post.
  • Is current drain less than 100 mA (or test lamp off)?
Yes
GO to H2.

No
GO to Component Tests to find the cause of ignition switch -OFF battery drain.

 

H2 CHECK FOR OPEN 'B+' CIRCUIT

  • Measure voltage at 'B+' terminal on the back of the generator , Circuit 38 (BK/O).
  • Is voltage at 'B+' terminal equal to battery voltage?
Yes
GO to H3.

No
CHECK fuse link in Circuit 38 and REPLACE if required. If OK, SERVICE open in Circuit 38 (BK/O).

 

H3 CHECK FOR OPEN 'A' CIRCUIT

  • Measure voltage at test point 'A' on the generator regulator .
  • Is voltage at test point 'A' equal to battery voltage?
Yes
GO to H4.

No
CHECK fuse in Circuit 36 and REPLACE if required. If OK, SERVICE open in Circuit 36 (Y/W).

 

H4 CHECK FOR OPEN FIELD CIRCUIT

  • Measure voltage at test point 'F' on the generator regulator .
  • Is voltage at test point 'F' equal to battery voltage?
Yes
GO to H5.

No
GO to H11.

 

H5 CHECK FOR OPEN 'I' CIRCUIT

  • Turn ignition switch to RUN position.
  • Measure voltage at wiring harness 'I' terminal, Circuit 904 (LG/R).

    NOTE: Generator regulator must be connected to wiring harness for this test.

  • Is voltage greater than 1 V?
Yes
GO to H6.

No
SERVICE open or high resistance in Circuit 904 (LG/R).

 

H6 CHECK VOLTAGE DROP IN 'A' CIRCUIT

  • Measure voltage drop between test point 'A' on the generator regulator and the positive (+) battery post.
  • Is voltage drop less than 0.25 V?
Yes
GO to H7.

No
SERVICE excess voltage drop in Circuit 36 (Y/W). CHECK fuse and connectors in Circuit 36 and SERVICE as required.

 

H7 CHECK FIELD TURN-ON

  • Measure voltage at test point 'F' on the generator regulator .
  • Is voltage at test point 'F' less than 2 V?
Yes
GO to H8.

No
GO to H11.

 

H8 CHECK FOR SHORTED RECTIFIER

  • Remove one-pin 'S' connector from generator .
  • Measure voltage between the 'S' terminal on the back of the generator and ground.
  • Measure voltage between the positive (+) battery terminal and the 'S' terminal on the back of the generator .
  • Is either voltage reading greater than 1 V?
Yes
REPLACE generator .

No
GO to H9.

 

H9 CHECK VOLTAGE DROP IN 'B+' CIRCUIT

  • Install 'S' connector.
  • Start engine.
  • Turn headlights ON and HIGH blower.
  • With engine running at 2000 rpm, measure voltage drop between the 'B+' terminal on the back of the generator and the positive (+) battery post.
  • Is voltage drop less than 0.5 V?
Yes
GO to H10.

No
SERVICE excess voltage drop in Circuit 38 (BK/O). CHECK fuse link in Circuit 38 and the connections between the battery and power distribution box.

 

H10 CHECK FOR OPEN STATOR PHASE

  • Connect test point 'F' on the generator regulator to the negative (-) battery post using a jumper wire.
  • Is generator output greater than the minimum output specified?
Yes
REPLACE generator regulator .

No
REPLACE generator .

 

H11 CHECK FOR OPEN/SHORTED FIELD

  • Remove generator from vehicle.
  • Remove generator regulator .
  • Measure resistance between the generator slip rings.
  • Is resistance greater than 10 ohms OR less than 1 ohm?
Yes
REPLACE generator .

No
CHECK for worn brushes (less than 8mm long) or open brush leads and REPLACE if required. If OK, REPLACE generator regulator .