M-1088 Electrical Problems

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NFDBOB

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Good Morning - I posted this previously in an incorrect forum and am sliding it over here - sorry for the confusion

I am responsible for taking care of two 1998 M-1088 Tractors that have been converted to fire department tanker use.

My problems are as follows:

1) One of the trucks will only start on a 24 volt jump pack and when the jump pack is removed the volt meter bounces all over the place, the transmission will not engage, and many times the truck will not shut down. If it was any other type of vehicle I would be thinking alternator or voltage regulator but with this unit I am not sure.

2) The other truck all of a sudden during an incident at 0200 this morning lost its headlights. All the other lights are still functional but not the headlights. Got to get it into the shop to verify that both didn't burn out but am very doubtful that I would have lost both high and low beams at the same time - any ideas?
 

coachgeo

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To help we need more information.... what year are the trucks.. what engine is in each. Different wiring for different years so these two answers will help determine what you have. Also will help us aim you toward the correct manuals
 

NFDBOB

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To help we need more information.... what year are the trucks.. what engine is in each. Different wiring for different years so these two answers will help determine what you have. Also will help us aim you toward the correct manuals
date of manufacture 092-98
date of delivery 09-98 D
 

tennmogger

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Suggestions: When the voltage looks bouncy on the dash voltmeter, Grab an ANALOG meter of the old type and start checking the voltage stability at:
- the output of the alternator, both 12v and 24v terminals. If 'bouncy', is it one or both voltages?
- If bouncy on one or the other, suspect alternator or regulator. Ifbouncy on both, measure the exciter voltage. Measure it against the alternator frame grounding point and the chassis nearby. Then measure the exciter voltage against battery grounds at the batteries (long test lead). The results should be the same at all points. If not then start checking ground connections. If the exciter voltage is bouncy, the output will be too.
- measure voltages at the dash panel (PDP-power distribution panel). If solid and correct, then the dash voltmeter's bounce is a local dash wiring problem. If the 12 and 24 at the PDP bounce, then back up to the PPD polarity protection device near the spare. Redo those connections.

Note that I have a 1996 "A0" LMTV that has a bouncy dash voltmeter. The voltages are correct and steady at the battery, at the PPD and at the PDP. And everything else works great. I have not gotten into the dash to find out why yet.
 

NDT

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I advised the OP that the truck with the jumpy voltmeter ONLY with the jump pack removed is a telltale sign of shot batteries that are not supplying reference voltage to the alternator. Caution: this jumpy voltage will fry things like the transmission controller!!
 

Suprman

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I always add a new big ground lead from the batteries negative to a sanded spot on the main frame rail. Then once you have known good batteries, measure 12 and 24 volts at the batts and then at the power panel lugs. You should only have around 1/2 volt drop at the panel. I would go thru and replace all the relays with new ones and use emery cloth on the breaker terminals. Look at the panel board contacts for corrosion also. If you lift the panel there is a ground on the right side of the cavity bolted up to one of the side handle bolts. Sand and use a lock washer make sure its a good contact. Once all that is good then you can move forward with troubleshooting any problems that remain.
 

19Detail

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As far as problem number 2 goes, there is a circuit breaker that controls just the headlights (CB 78). It is the only self resetting CB in the panel. I know this because the same thing happened to me several times on my way back from TX. My headlights always came back on after a fashion and I was told the M Series light switch was most likely the culprit. I have since removed that switch from the truck and have not noticed the problem since, but to be fair, I have not driven it as much at night to give it a thorough test.
 

Reworked LMTV

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I lost the headlights on mine suddenly. Turns out it was the turn signal. I took the turn signal apart. I do not recommend that you do this. Lots of things can break from what I could see. Small springs and plastic parts. $200 for replacement new.

Bouncing meter may indicate AC at the gauge, and thus the rectifier / voltage regulator on alternator might be bad. There IS an AC output on some alternators, used for tachometers, etc. Unless someone messed with the alternator recently, this is not likely the issue. C.E. Neihoff has a troubleshooting for alternator on their website.

Good Morning - I posted this previously in an incorrect forum and am sliding it over here - sorry for the confusion

I am responsible for taking care of two 1998 M-1088 Tractors that have been converted to fire department tanker use.

My problems are as follows:

1) One of the trucks will only start on a 24 volt jump pack and when the jump pack is removed the volt meter bounces all over the place, the transmission will not engage, and many times the truck will not shut down. If it was any other type of vehicle I would be thinking alternator or voltage regulator but with this unit I am not sure.

2) The other truck all of a sudden during an incident at 0200 this morning lost its headlights. All the other lights are still functional but not the headlights. Got to get it into the shop to verify that both didn't burn out but am very doubtful that I would have lost both high and low beams at the same time - any ideas?
 
Last edited:

SausageGuy

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I lost the headlights on mine suddenly. Turns out it was the turn signal. I took the turn signal apart. I do not recommend that you do this. Lots of things can break from what I could see. Small springs and plastic parts. $200 for replacement new.
Lost my headlights last week when I hit highbeams pulling into my driveway. Figured turn signal switch but have not had time to look at it. Where did you find them?

Also my voltmeter was jumping but over a couple months kept getting lower and lower then alternator went out. I just thought it was a gauge issue.
 

Ronmar

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Problem 1 sounds like bad batteries or connections. The alternator when commanded to excite by the oil pressure circuit will attempt to supply voltage to its regulated level. If it doesn't see the response/interaction it is expecting from the battery bank(particularly the 12 to 24v relationship) it stops, resets and tries again(pulses)...
 

Reworked LMTV

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http://rometruckparts.com


I carry a spare one too.

Lost my headlights last week when I hit highbeams pulling into my driveway. Figured turn signal switch but have not had time to look at it. Where did you find them?

Also my voltmeter was jumping but over a couple months kept getting lower and lower then alternator went out. I just thought it was a gauge issue.
 

snowtrac nome

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western alaska
If you lost the high beams only there is a harness of the bottom of the fuse box that will burn the pin out, especially if you add a set of driving lights or ho high beam head lights. Mine is messed up and I have to get in and jumper around it.
 

coachgeo

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If you lost the high beams only there is a harness of the bottom of the fuse box that will burn the pin out, especially if you add a set of driving lights or ho high beam head lights. Mine is messed up and I have to get in and jumper around it.
If you don't mind next time your at a schematic can you put the wire and harness out via a cut/paste orrr?? or better yet; if physically in that area of the truck..... shoot a pic of the harness and pin your referring too along with the jumper. Have high output lights and was not aware this may be an issue ....... so want to prepare
 

NFDBOB

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Massachusetts
Good Morning - so working with some other personnel we determined that the batteries on problem #1 are more than likely completely junk (when we hit them with a load tester they drop completely off the scale and shut down the digital meter) - those are on order and should be in later on today.

As for the headlight issue I am still wondering if there is a wiring diagram somewhere that might be online? I have been told that there is a circuit breaker of some sort under the passenger side dash panel but really don't want to start tearing things apart if it doesn't truly exist under there.....
 

coachgeo

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.... I have been told that there is a circuit breaker of some sort under the passenger side dash panel but really don't want to start tearing things apart if it doesn't truly exist under there.....
all the wiring diagrams are in the TM's IFF it is an A0 (older model) some of the older of the A1's the diagram is also available. that being said the A0's are available HERE on this board . Front page of this board is a section called...... "Technical Manuals" Go there then go "Present Conflict" and search it for LMTV and the thread with all the manual download links will show up. If you have an older model A1.... see classifieds.

A0 mostly have 3116 engine
A1 mostly has 3126 or C7 engines

believe your 1998 are right on the edge of being one or the other.
 
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NFDBOB

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Massachusetts
Argh --- I hate waiting on deliveries. And of course the truck didn't make the boat so no batteries today. Here is hoping tomorrow lets me get this thing operational again
 
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