Electrical voltage

[Strong50]

Hey guys. Before I ask, i'll let you know that I have read through the threads and have followed as many directions as possible. As of last week I have been experiencing some voltage irregularities in my M1088. I have 14 and 28 volts at the alternator, I have 13 and 27 at the lugs on the dash.

I've seen the voltage meter on the dash drop to 20 and have had some delayed gear shifting. The Headlights are dimming, my back up cameras are turning off.

I pulled all the wires on the batteries and cleaned the connections. I cleaned all the connection behind the cab under the spare tire carrier. The batteries are Exide group 31's and are 8 months old.

What Am I missing?

 

[coachgeo]

If it is an A0 one guess is the exciter wire. Via advanced search of this forum (or adv. google search) search for ( Excite... or Exciter, solenoid - posted via user name Suprman ). He has mentioned this tons of times and reading thru a few of them will piece it together for you.

The exciter wire "excites" the alternator to begin charging. If it is not excited you do not have 24v charge sent to the batteries. Off top of my head not sure if other places only get there 24v from alternator..... if so these will obviously be affected too.

Here is one I found that mentions the fix. Post 5- 7 or 8 is a good start. https://www.steelsoldiers.com/showt...016&highlight=excit+wire+solenoid#post2042016



The A1's are little different when it comes to the excite wire if I recall right but below should still hold true for either model.

check the 24v terminal inside the fuse panel is tight? check / un-plug and replug all the units in there as well to make sure they are all seated good.


hmm.. might check the power switch itself. Maybe terminals on back of it are loose??


Besides that.... check grounds. Thick there is a big one in area of battery box.


Have you used your TM's to help diagnose?

 

[Awesomeness]

I had your symptoms once when one of the alternator cables had worn through and shorted against a bracket. Every time it would hit and make contact, I'd get the "drop outs" you are talking about, and the transmission dash panel would reset. I think almost any of the larger wires shorting like this could cause it.

That may not be your problem, but it's one of the possibilities.

 

[tennmogger]

How are your batteries? If the batteries are tending toward high cell resistance due to old age or poor charging history, the voltage regulator sees the charge voltage peak out of range and cuts back on alternator output. The dash meter can drop well into the yellow. If you are just sitting with the engine idling then the alternator output is not so high and the measured voltages look good, as you are seeing. You know your alternator and regulator are good.

When that happened on my truck I replaced the batteries and that fixed it. These trucks will start on poor batteries quite well. That 5 second starting draw does not kill even a dead-ish battery. When I tested the batteries taken out, the electrically 'top' two, rearmost in the box, were both bad.

 

[Suprman]

Cab power goes thru the reverse polarity box. Its basically a diode array. You get 1/3 to 1/2 volt drop thru it. So the cab voltage will be slightly lower than the alternator output. But I would check all cables and connections. I would replace the dash power relay. I would make sure your excitation lead on the alternator regulator is good, if not I would abandon the factory lead and tap off the fuel solenoid positive come around the front of the motor to the front connection on the regulator.

 

[mechanicjim]

on the voltage regulator there are two LEDs one for 14v and one for 28V what are they doing when the voltage drops?
according to your post at alt 14v and 28v, but at dash 13 and 27v this is a one volt drop not ideal max you would like is 1/2 volt drop at most, clean the grounds and B+ wires,
when the voltage drops that is because the alternator is no longer charging and you are basically running off battery alone, that why everything starts to power off.
do you have the LBCD(load and battery control device)? its the box with 4 post on it that goes between battery and alternator if you do this also has an LED see what that is doing when you loose power if you have it.

it sounds like what coachgeo says the regulator loose Excite and then your just running on battery which causes all the other symptoms.

 

[Strong50]

Gentlemen. Once again thank you for the suggestions. I’ll run though all of that one by one this week and let you know. I also have one of the reserve center mechanics coming by this week to help with it.

 

[wheelspinner]

Gentlemen. Once again thank you for the suggestions. I’ll run though all of that one by one this week and let you know. I also have one of the reserve center mechanics coming by this week to help with it.

You didn't say you had a ringer in your pocket. Will be interesting to see what their findings are.

 

[Awesomeness]

You didn't say you had a ringer in your pocket. Will be interesting to see what their findings are.

He'll spend a few hours following the troubleshooting charts in the TM, fail to diagnose the problem, and tell you to sell the truck at auction?

 

[Strong50]

You didn't say you had a ringer in your pocket. Will be interesting to see what their findings are.

I have tried and tried to become more mechanically inclined, but to no avail. I develop buildings for a living and can build anything with an address.

I stopped my the reserve center which is next door to the National Guard Depot and they have full time Mechanics who do not mind working for free beer and $30.00 an hour. Hopefully with your suggestions we can get this resolved this week.

 

[Strong50]

Ok guys. The reserve Mechanic couldn’t come this weekend and i have a couple hours to throw at my problem.
I have 14.1 on the yellow Alt terminal
I have 28.4 on the red Alt terminal

my regulator does not have LED lights but the forward terminal has 2.4 volts? The back terminal has 22.3v. Does that mean it is my excite wire?

 

[Strong50]

Here is one I found that mentions the fix. Post 5- 7 or 8 is a good start. https://www.steelsoldiers.com/showt...016&highlight=excit+wire+solenoid#post2042016

Are the fuseable Links the thick colored yellow and red washers on the ALT Terminals?

 

[Suprman]

With the engine running, take a measurement of the front terminal on the regulator wire. It has to be disconnected from the regulator to take the measurement.

 

[Strong50]

With the engine running, take a measurement of the front terminal on the regulator wire. It has to be disconnected from the regulator to take the measurement.

do i disconnect the negatives on the batteries to remove the regulator wires?

 

[Suprman]

No. Only disconnect the front regulator lead and take a voltage measurement on that wire with the engine running. Do not disconnect anything else. You should check all of your battery terminals and alternator connections make sure they are on tight.

 

[Strong50]

The wire reads 0

 

[Suprman]

You need 24v at the front terminal on the regulator to excite the alternator. There is an excitation relay in the panel. It is possible that someone switched the front and back leads. The rear terminal should be a field sense on the older alternators but it’s an ac voltage output on the newer models. You can leave the dead lead off and jump 24v from the fuel solenoid positive run around the front of the motor to the front regulator terminal see if starts making good voltage.

 

[Strong50]

Are you saying that it’s possible that i should Switch the front and back lead?

 

[Suprman]

I would run a new one

 

[Strong50]

Roger that. Thank you