Wire gauge

[usmcgunner]

Just picked up an M1008. I noticed, among a couple of related items, that the wire going from the front battery (batt 1?) to the rear battery is a much smaller gauge than the rest of the main cables. Is this normal? Or should all the cables be the same size. Semi-related issues....headlights are very dim and the voltage off of batt 1 is lower than batt 2 (rear) while running. Once again, normal?

 

[richingalveston]

no, battery cables should all be the same size but the large cables are for starting only. The 12volts is delivered to the truck from the neg terminal of the rear battery assuming it is still a 24v truck. You should see a smaller wire that leaves the rear negative battery terminal and goes to a two terminal power block on the drivers side of the fire wall (next to relay). This smaller wire is what feeds all of the 12V equipment in the truck. If your lights are dim then you have a problem in your headlight harness or some bad grounds causing a drag on the battery.

check battery voltage with lights off, and with them on. if it only happens when lights are on then the problem is probably in the headlight harness. To help alleviate a bad headlight harness, get the heavy duty harness with relays from LMC. however, with this harnes you still need to fix bad grounds and any also any other bad wiring. This new harness just reduces the load on your factory wiring wich will keep things from burning up in the future.

 

[usmcgunner]

Thanks man. Would you happen to know the correct size or recommended size? I think I'm just going to replace all the heavy stuff and the batt terminals. I was thinking either 6 or 8.

 

[Warthog]

The wire sizes are listed in the wiring diagrams. You need to read the first few pages of the Troubleshooting section to see how the wires are labeled and what the numbers mean.

 

[richingalveston]

becareful when replacing the wires, you will see some of the wires are crimped to smaller wires before they make the final connection. These smaller sections are the fuse.
Your wiring harness has no fuses, it uses whats called fusable links. the small section of wire is supposed to burn before the rest of the wire durring overload and short situations. replacing the wires in many cases will remove the links thus you can fry a lot of stuff if you do not know what you are doing.

my recomendation would be to fix your truck back to stock. with the exception of converting your glow plugs to 12v, doing doghead relay, and adding heavy duty headlight harness. with these mods done, your stock wiring will be very reliable.

 

[Warthog]

Post some pics of what you have. The stock wire size for the batteries is 2 gauge.

 

[usmcgunner]

Thanks. I missed it or didn't look at the right schematic. I'm at work right now, so I'll pop some pics up tomorrow when I start tinkering around. There appears to be a "few extra wires" under the hood from when the Forestry service had it.

 

[Warthog]

The forestry service was very good at adding additional wiring, no matter what part of the US they where located.

 

[usmcgunner]

So here it is. The uploads might end up being out of order. Front batt picture shows the cable from the front batt to the rear. The gauge marked on it is 4. So I guess I'll be replacing that. Any good sources on batt cable in 2 gauge? I've found plenty of 4g and some 2g in black. Next is the interesting little yellow wire which I assume is trying to be a ground. As you can see, it screws directly to the body. Next is a little red (I think 10g) coming off the rear batt going to just behind the air cleaner in the last picture. Some sorta little terminal thingy that it connects to on the left post. It changes to green right behind that windshield wiper fluid hose (hmmm).

 

[Warthog]

The factory wiring terminals have been replaced. They did rewire it the same a stock.

1) The yellow wire is a ground. The factory wire was black and was attached to the radiator support. It was 10 gauge.

2) The smaller red wire on the rear battery feeds the diamond shaped 12v Positive terminal block on the firewall. The wire has a blue fusible link where it attaches to the 12v block. This wire is stock. It is 8 guage

3) the 24V restistor pack for the glowplugs has been bypassed (good thing). They disconnected the wire on the right side on the resistors and attached the wire to the 12v Terminal block.

4) The two batteries are tied together with a 4 gauge wire. Your is the stock size.

You may want to replace the battery cables since you have no idea of the condition. Stock cables are not avaiable except used.

Going back to the first post, are your GEN ligts working when you first start the truck? They must work indorder for the alternators to work.

 

[usmcgunner]

Thanks man. Yup. Gen lights are both on when I key on. After a slightly long start, they both go off. Which is a good transition point to maybe a related topic. I've only seen the WAIT light once. When I first picked up the truck, the PO said that there seemed to be a "rattling" noise coming from something related to the glow plugs/relay. Haven't found that relay yet to check it because I haven't heard it since pickup either. (just like the light). I need to do the voltmeter/glow plug test tomorrow to see if I'm getting power, but I'm guessing a bad relay. Once again, just have to research and find it.

As for the dim lights, I metered them last night and I'm getting about a half volt drop on batt 1 when they're on. 12.3 off 11.7/8 when on. New wiring harness is on the way and I've already picked up new bulbs.

Know of a good source for the battery terminals? I can only find 4g on multi-post terminals.

Lastly, what is that terminal block on the firewall that I pointed out in the picture?

 

[Whitfield]

My biggest headlight issue was the spade plugs and terminals at the headlights themselves, a small screw driver and some 200 grit sand paper got them working again for now.

Battery cables / Terminal ends. The two of the best sources I've found locally are, A big over the road truck repair shop or a fork lift repair shop. Either of these places make a living off of stocking / installing dependable heavy gauge battery cable connections. Terminal block on the firewall (in pic 4) is the stock GM 12v terminal block. Glow plug relay is silver and to the lower right in that picture. A new 1986 Ford 6.9L glow plug sylinoid part # GPR7 is a nice easy $20 replacment + flip it upside down and it is a perfect fit.

 

[usmcgunner]

Thanks for all the info. I'll put a hold on this thread for a bit until I take care of the items covered so far. Don't want to get too far ahead. I just placed a huge LMC order, so once that comes in and I catch up the work, I'll report back.

 

[Warthog]

Sorry for letting this thread get sidetracked. Lets keep it simple for now and learn all the hard stuff later.

You current wiring works, you might need some new cables and terminal ends. Fix what you have and then get into all the theory about isolated ground alternators, dual batteries , current flow, etc.

Now to your questions.

1) the diamond shaped thingy on the firewall is the 12v Engine Wiring Harness Block (EWHB). This is where all the 12v circuits for the truck originate. 12v is coming from the front battery via the red wire from picture #3. The "green" wire started out as blue and has faded. The blue wire is the fusable link for the 12v circuit. Power then goes out to the fusebox and other circuits.

2) The glowplug relay is the silver cylinder item next to the 12v EWHB (picture #4). In a stock system it is controlled by the Glowplug Controller Card in the cab. Normally it is fed 24v from the 24v Positive Terminal Board (behind the rear battery). Your truck has been modified to feed the glowplugs only 12v. That is the larger red wire in Pic#4 that is attached to the 12v EWHB

3)From your description, your GEN1(drivers side) alternator is not working properly. The 12.3v from battery1(front) is just battery voltage. A fully charged battery should read ~12.7v and a fully fuctional alternator should read ~14.4v. That would help explain your dim headlights. The alternator may need to be rebuilt.

You need to see if both of your alternators work properly, see if you batteries are good and then learn what all the different parts of the truck are.