MCI coaches have been equipped with Delco alternators and external regulators for many years. When working properly, this charging system provides up to 270 amps of 24 volt power to the coach electrical system. It can be very confusing and time consuming to troubleshoot this system if it is not working properly, so a troubleshooting guide has been created to assist in following specific steps to determine the cause of the system failure.
This guide is created in the form of a series of questions that require yes and no answers, and applies to all MCI coaches equipped with Delco alternators prior to the D4000 and D4500 equipped with multiplex (MUX) electrical systems. Each answer directs you to the next step in the troubleshooting sequence. This guide can be printed out, or you can utilize it directly off of the MCI website. When using the Internet, selecting the underlined yes and no answers will automatically advance you to the next step.
| STEP |
CONDITION |
ACTION |
RESULT |
GO TO |
| 1 |
Engine running; Air pressure built up. |
Alternator is not charging and "no gen" tell tale light at the dash is on. |
Yes
No |
Step 2
Step 26 |
| 2 |
Engine running. |
Check stud #33 located in the rear electrical box for 12 volts. |
Yes
No |
Step 9
Step 3 |
| 3 |
Engine running. |
Check stud #49 located in the rear electrical box for 24 volts. |
Yes
No |
Step 4
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
No |
Step 6
Step 49 |
| 6 |
Engine stopped; Master on. |
Check "F1" on the voltage regulator located in the #3 baggage compartment for output voltage. |
Yes
No |
Step 17
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
No |
Step 18
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
No |
Step 15
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
No |
Step 10
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
No |
Step 11
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
No |
Step 13
Step 38 |
| 13 |
|
Go to the field relay located in the rear electrical box and check pins 3 & 6 for 24 volts. |
Yes
No |
Step 14
Step 33 |
| 14 |
|
Go to stud #49 located in the rear electrical box and check for 24 volts. |
Yes
No |
Step 4
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
Open
Shorted |
Step 16
Step 22
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
No |
Step 11
Step 22 |
| 17 |
Engine running. |
Check for 12 volts on stud #33 located in the rear electrical box. |
Yes
No |
Step 54
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
No |
Step 7
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
No |
Step 42
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
No |
Step 10
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
No |
Step 2
Step 27 |
| 27 |
|
Replace light bulb (part #19-11-1105) in the tell tale cluster at the dash. |
Yes
No |
Step 26
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
No |
Step 32
Step 29 |
| 29 |
|
Check circuit breaker #54 (load side) for 24 volts on the master buss bar located in the rear electrical box. |
Yes
No |
Step 45
Step 31 |
| 30 |
Engine running. |
Check relay terminal on alternator for 12 volts. |
Yes
No |
Step 10
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
No |
Step 36
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
No |
Step 34
Step 51 |
| 34 |
Engine stopped; Master off. |
Check pin #2 on the field relay located in the rear electrical box for a ground. |
Yes
No |
Step 35
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
No |
Step 54
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
No |
Step 46
Step 40 |
| 38 |
|
Check for power on circuit breaker "A" (load side) on battery buss bar located in the rear electrical box. |
Yes
No |
Step 48
Step 45 |
| 39 |
Engine stopped; Master off. |
Check stud #47 located in the rear electrical box for ground. |
Yes
No |
Step 47
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
No |
Step 44
Step 22 |
| 53 |
Engine stopped; Master on. |
Check "FLD" terminal on alternator for battery voltage. |
Yes
No |
Step 15
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
No |
Step 55
Step 1 |
| 55 |
|
Make sure that all clamps, terminals, relays and covers are secured. |
|
Job Done |
This generator check-out guide was created from extensive research conducted by Lanny Martin. If you have any questions, please call the MCI Customer Support Center at (800) 241-2947.
