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Electrical system overview

Mrav8r

New member
5
2
3
Location
Tuttle, OK
I just bought an 84 M1008 through a surplus auction. I have rebuilt several old Chevy trucks, but I am wanting to read up on the electrical system so I can understand the differences. This forum is great for specific issues, but reading through the threads it seems there is a lot of tribal knowledge and underlying experience on this site that I don't have. I would like to catch up so I understand what I'm seeing on the truck and reading on this site. What's the best place to start to get a good overview of the system?
 

Skinny

Well-known member
2,130
486
83
Location
Portsmouth, NH
Do you have an understanding of basic electricity? If not, I would pick up a basic automotive instruction book or start combing through through the YouTubes to understand how the principles work.

When you have the basics of volts, amps, ohms, then figure out how to read a basic wiring diagram. Again, a basic college level book will walk you through what all the symbols mean.

Somewhere on here you will find all the wiring diagrams with colors. That is the easiest way to trace the circuits unless you have a way to blow up the image in the manuals. I just have them printed out and they are pretty easy to follow with your finger.


Sent from my Moto G (5) Plus using Tapatalk
 

MarcusOReallyus

Well-known member
4,524
808
113
Location
Virginia
There are some excellent resources for you in the Helpful Threads sticky (top of the forum), including several good overview threads. Great place to start!

And of course, you'll want to download the TMs from this site. Freebies!

Pop back here with any specific questions you have, and we'll do our best to confuse the living daylights out of you! :D
 

Keith_J

Well-known member
3,657
1,313
113
Location
Schertz TX
Only the starter and glow plugs use 24 volt, all other systems are 12 volt. The alternators are 12 volt using one for each battery. The back battery and passenger side alternator are 12 to 24 volt, the front battery and driver's side alternator are 0 to 12 volt.

This means the passenger alternator must have isolated negative which is connected to the front battery positive terminal..actually connected to the rear battery negative but the two are the same.

If you understand home wiring with 120/240 , the CUCV is similar.
 

Mrav8r

New member
5
2
3
Location
Tuttle, OK
There are some excellent resources for you in the Helpful Threads sticky (top of the forum), including several good overview threads. Great place to start!

And of course, you'll want to download the TMs from this site. Freebies!

Pop back here with any specific questions you have, and we'll do our best to confuse the living daylights out of you! :D
Thanks, I booked marked the page and will take a look. I downloaded the maint and parts TMs.
 

Mrav8r

New member
5
2
3
Location
Tuttle, OK
Do you have an understanding of basic electricity? If not, I would pick up a basic automotive instruction book or start combing through through the YouTubes to understand how the principles work.

When you have the basics of volts, amps, ohms, then figure out how to read a basic wiring diagram. Again, a basic college level book will walk you through what all the symbols mean.

Somewhere on here you will find all the wiring diagrams with colors. That is the easiest way to trace the circuits unless you have a way to blow up the image in the manuals. I just have them printed out and they are pretty easy to follow with your finger.


Sent from my Moto G (5) Plus using Tapatalk
Thanks, yes I understand electricity. I was an aircraft mech for 19 years, and have completely rewired a couple of old chevy trucks. Just trying to figure out the 24/12 V thing and the reason for all these damn relays and circuit boards. Half temped to cut all that crap out and drop in a crate engine, but I want to give this thing a chance since I was able to get the engine running fairly easily.
 

Mrav8r

New member
5
2
3
Location
Tuttle, OK
I just bought an 84 M1008 through a surplus auction. I have rebuilt several old Chevy trucks, but I am wanting to read up on the electrical system so I can understand the differences. This forum is great for specific issues, but reading through the threads it seems there is a lot of tribal knowledge and underlying experience on this site that I don't have. I would like to catch up so I understand what I'm seeing on the truck and reading on this site. What's the best place to start to get a good overview of the system?
This is what I was looking for, thanks. https://www.steelsoldiers.com/threads/cucv-alternator-isolated-ground-therory-of-operation.60958/
 

MarcusOReallyus

Well-known member
4,524
808
113
Location
Virginia
Thanks, yes I understand electricity. I was an aircraft mech for 19 years, and have completely rewired a couple of old chevy trucks. Just trying to figure out the 24/12 V thing and the reason for all these damn relays and circuit boards.


There is nothing complicated or at all unusual about the "relays and circuit boards" on these vehicles. The starter circuit has a relay under the dash which drives the relay (solenoid) on the starter. That's a box stock setup for a ton of vehicles. There is nothing unusual or complicated about it. One side is 24v, one side is 12v, and that's it.

The GPs have a relay controlled by an intelligent circuit board. Again, that's a box stock setup for a ton of vehicles. There is nothing unusual or complicated about it.


Half temped to cut all that crap out and drop in a crate engine
You would still need exactly the same circuit boards and relays as you have now. But you'd probably have butchered the wiring in the process and be in the middle of a nightmare.

The ONLY thing different about this beast is the 24/12v system, and that doesn't involve any relays or circuit boards. There are only TWO components that are different from stock:
  1. The GP resistor bank on the firewall. No relays, no circuit board, no moving parts, almost foolproof. (And easily removed, if you don't like it.)
  2. The isolated ground alternator on the driver's side. Except for a few extra insulators, it's a box stock Delco 27SI. Nothing complicated.

Now, there are a few minor military doo-dads that might bug you. There are some diodes scattered around that are there for radio noise suppression. They sometimes cause problems, and the easiest solution is to just cut them out and throw them away. Done.

The blackout light switches can be annoying. You brush the switch wrong and suddenly you lose all your lights. Then you go crazy trying to figure out why because you forgot to check the switch first. Doesn't seem to bother most people, but if it does, you can always bypass the switch. I have a thread on how to do that. Just a few simple jumpers and it's 100% easily reversed.

If you really, really can't work with the 24/12 system, there is a simple, standardized conversion to pure 12v called the Roscommon method, and it's documented here on the site.

No crate engine required.
 

TexasM1079

1998 S&S LMTV M1079
7
1
1
Location
Dallas TX
Any way you can point me to the wiring diagram for my 1998 M1079 ? I can't find it on any threads. My S&S dealer is installing my AC system and can't get the AC clutch to engage (which I realize could be for more than one reason). Thanks in advance. Dan C.
 

Keith_J

Well-known member
3,657
1,313
113
Location
Schertz TX
The diodes are there to block reverse current, not for radio noise suppression. Capacitors are used for radio noise suppression.
 
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