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The Dog House

No Gen Light Troubleshooting Chart

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For MC12 thru D models 

‘Not Generating Troubleshooting Guide’

 

1 Engine running; Air pressure built up. Alternator is not charging and "no gen" tell tale light at the dash is on.

Yes Step 2

No Step 26

2 Engine running. Check stud #33 located in the rear electrical box for 12 volts.

Yes Step 9

No Step 3

3 Engine running. Check stud #49 located in the rear electrical box for 24 volts.

Yes Step 4

No Step 12

4 Engine running. Check stud #48 located in the rear electrical box for 6 to 11 volts (voltage depends on the condition of the batteries and output of the alternator).

Yes Step 52

Stud #48 reads battery voltage (24 volts). Yes Step 53

Stud #48 reads 0 to 5 volts. Yes Step 5

5 Engine stopped; Master on. Remove cover on voltage regulator located in the #3 baggage compartment. Check for 24 volt power. (On old regulator part #7G-4-1, terminal marked "A1". On new regulator part #07-04-1001, terminal marked "A1, Ing.")

Yes Step 6

No Step 49

6 Engine stopped; Master on. Check "F1" on the voltage regulator located in the #3 baggage compartment for output voltage.

Yes Step 17

No Step 19

7 Engine stopped; Master off. Remove "F1" wire located in the #3 baggage compartment from the voltage regulator "F1" terminal, and measure the resistance of the wire to chassis ground. It should read 3 to 5 ohms of resistance.

Yes Step 18

No Step 8

8 Engine stopped; Master off. Remove the "F1" wire located in the #3 baggage compartment from the "FLD" terminal on the alternator (tape it up and make sure that it is not touching anything). Read the resistance of the "F1" wire. It should read Infinity.

Yes Step 15

No Step 42

9 Engine running. Check for a ground on pin #7 of the discharge and blower relay located in the rear electrical box.

Yes Step 10

No Step 43

 

 

10 Engine stopped; Master off. Check for a ground on pin #7 of the discharge and blower relay located in the rear electrical box.

Yes Step 11

No Step 24

11 Replace the discharge and blower relay located in the rear electrical box with 12 volt relay part #7D-5-1. Continue Step 54

12 Go to the field relay located in the rear electrical box and check pins 1 & 8 for 24 volts.

Yes Step 13

No Step 38

13 Go to the field relay located in the rear electrical box and check pins 3 & 6 for 24 volts.

Yes Step 14

No Step 33

14 Go to stud #49 located in the rear electrical box and check for 24 volts.

Yes Step 4

No Step 50

15 Engine stopped; Master off. Remove wire "F1" off the "FLD" terminal on the alternator. Meter the resistance of the "FLD" terminal. It should meter 3 to 5 ohms of resistance.

Yes Step 16

Open Step 22

Shorted Step 21

16 Engine stopped; Master off; Main disconnect on. Remove wire "R1" off the relay terminal on the alternator. Meter the voltage of relay terminal. It should be less than 1.5 volts.

Yes Step 11

No Step 22

17 Engine running. Check for 12 volts on stud #33 located in the rear electrical box.

Yes Step 54

No Step 30

18 Engine stopped; Master off. Make sure that wires are hooked back up to the alternator - "F1" to "FLD" terminal and "R1" to relay terminal. Replace the voltage regulator and put "A1" wire on "A1" or "POS" terminal (with new style regulator, hook up to "B").

Continue Step 53

19 Check for a ground on "NEG" of the voltage regulator ("G" on the new regulator) located in the #3 baggage compartment.

Yes Step 7

No Step 49

20 Engine stopped; Master off. Remove wire "F1" from the "FLD" terminal on the alternator. Meter the resistance of "FLD" terminal. It should meter 3 to 5 ohms of resistance.

Yes Step 42

No Step 21

21 Engine stopped; Master off; Main disconnect off. Change out the alternator and the voltage regulator.

Continue Step 23

22 Engine stopped; Master off; Main disconnect off. Change out the alternator.

Continue Step 23

23 After installing new alternator, pull the field relay located in the rear electrical box and run engine for five minutes. Stop engine and plug in the field relay.

Continue Step 52

24 Prior to unit #47071 - Check for a ground from the low air switch located in the rear electrical box. Effective with unit #47471 - Check ground studs located in the rear electrical box.

Yes Step 10

No Step 25

25 Prior to unit #47071 - Replace low air switch located in the rear electrical box. Effective with unit # 47071 - Clean and repair ground studs located in the rear electrical box.

Continue Step 10

26 Push the press to test button and see if the "no gen" tell tale comes on at the dash.

Yes Step 2

No Step 27

27 Replace light bulb (part #19-11-1105) in the tell tale cluster at the dash.

Yes Step 26

No Step 28

28 Engine stopped; Master on. Check for 24 volts on pin #1 of the discharge and blower relay located in the rear electrical box.

Yes Step 32

No Step 29

29 Check circuit breaker #54 (load side) for 24 volts on the master buss bar located in the rear electrical box.

Yes Step 45

No Step 31

30 Engine running. Check relay terminal on alternator for 12 volts.

Yes Step 10

No Step 22

31 Remove and replace circuit breaker #54 located in the rear electrical box; part #7C-13-127.

Continue Step 28

32 Engine stopped; Master on. Check pin #4 of the discharge and blower relay located in the rear electrical box for 24 volts.

Yes Step 36

No Step 11

 

33 Engine stopped; Master on. Check for 24 volts on pin #7 on the field relay located in the rear electrical box.

Yes Step 34

No Step 51

34 Engine stopped; Master off. Check pin #2 on the field relay located in the rear electrical box for a ground.

Yes Step 35

No Step 39

35 Check the field relay terminals located in the rear electrical box, and replace field relay, part #7D-5-24.

Continue Step 36

36 Engine stopped; Master on. Check for 24 volts on stud #49 located in the rear electrical box.

Yes Step 54

No Step 12

37 Check for 24 volts on battery buss bar on the load side of circuit breaker "A" (15 amp) located in the rear electrical box.

Yes Step 46

No Step 40

38 Check for power on circuit breaker "A" (load side) on battery buss bar located in the rear electrical box.

Yes Step 48

No Step 45

39 Engine stopped; Master off. Check stud #47 located in the rear electrical box for ground.

Yes Step 47

No Step 41

40 Remove and replace circuit breaker "A", part #7C-13-127, located in the rear electrical box.

Continue Step 36

41 Remove and replace triple function protective device located in the rear electrical box.

Continue Step 36

42 Repair or replace harness from the voltage regulator to stud #48 located in the rear electrical box to alternator "FLD" terminal.

Continue Step 18

43 Repair or replace the jumper wire with diode assembly from stud #33 located in the rear electrical box to pin #2 on the blower discharge and cut-in relay.

Continue Step 54

44 Repair or replace harness from relay terminal of the alternator to stud #33 located in the rear electrical box and F1 terminal of the alternator to stud #48 in the rear electrical box.

Continue Step 54

 

45 Repair or replace jumper from circuit breaker #54 located in the rear electrical box to pin #1 on discharge and blower relay.

Continue Step 28

46 Repair or replace the jumper from circuit breaker "A" located in the rear electrical box to field relay pin #'s 8 & 1.

Continue Step 13

47 Repair or replace jumper wire from pin #2 on the field relay located in the rear electrical box to stud #47.

Continue Step 36

48 Repair or replace wire from circuit breaker "A" on the battery buss bar located in the rear electrical box to pin #'s 1 & 8 on field relay.

Continue Step 12

49 Repair or replace harness from stud #49 located in the rear electrical box to voltage regulator "A1" terminal; stud #48 in the rear electrical box to "F1" terminal on voltage regulator; and ground stud in the rear electrical box to "NEG" on voltage regulator and jumper to mounting box.

Continue Step 6

50 In the rear electrical box, repair or replace jumper between field relay pin #'s 3 & 6 and stud #49.

Continue Step 36

51 Repair or replace jumper between studs 24 & 25 located in the rear electrical box and pin #7 on field relay.

Continue Step 36

52 Engine running Measure the voltage on "R1" terminal of the alternator for 12 volts.

Yes Step 44

No Step 22

53 Engine stopped; Master on. Check "FLD" terminal on alternator for battery voltage.

Yes Step 15

No Step 44

54 Engine running on fast idle and charging; Head lights and exterior lights on. Check or adjust the voltage regulator to 27.5 volts.

Yes Step 55

No Step 1

55 Make sure that all clamps, terminals, relays and covers are secured. Job Done

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