Electrical issues

[Joey7]

So I've been having a handful of electrical issues on my m1008 for the last few weeks and I can't figure it out nore find a solution anywhere.

The biggest issue is starting. Both batteries are around 12v (ones been around 11.8 most the time) but I'm not even getting a crank most the time without jumping both batteries.

I'm getting 24v at the starter, and when I went to hotwire it between the wiring and it cranked without an issue.

Granted the two batteries are both 650cca I believe. Just because I wanted to eliminate my batteries being the problem especially after one of them tested bad. But as soon as I left them on the charger they both went right up to 12.6. but once the trucks starts, my stereo starts turning on and off after a few minutes, then completely shuts off, and I slowly loose accessory power, as well as all nights, blinkers, ect. Even when the batteries are for the most part full.

I have an generator light on. But only one, I think an alternators out but I haven't been able to check it. But unless both alternators are out I can't imagine that's the main issue

If turning the key does anything, it clicks like I don't have enough voltage. But most the time I turn it over only for nothing to happen.

I'm assuming on top of an alternator being out, my ignition switch, or the starters out. But that wouldn't explain the rest of the electrical issues. That's why I'm wondering if a short somewhere would be draining voltage somehow. Or if there's a relay I'm missing. Any advice would be appreciated, thanks

 

[Keith_J]

11.8 volts is very weak. Both need to be 12.5 volts or more. 650 CCA is also weak. Test alternators per the sticky thread at the top of this forum, then load test batteries after a full charge.

 

[Joey7]

11.8 volts is very weak. Both need to be 12.5 volts or more. 650 CCA is also weak. Test alternators per the sticky thread at the top of this forum, then load test batteries after a full charge.

I have my original batteries, but both were reading low so I threw on the 650cca ones mainly for testing. But now my good batteries are charging no problem off of the truck. I tested my alternators yesterday just with the regular multimeter test. Regardless of which alternator was disconnected my main battery (closest to the cab) was staying right around 12.6v when it was running, and the other battery immediately starts dropping around .1v a second. So I'm leaning towards both alternators being out, or maybe a short somewhere draining voltage

 

[GunnyM1009]

I would study the exciter circuit for the alternators before assuming both are bad. I had thought the same thing till I looked in to how that circuit runs thanks to some advice from the SS forum. Turned out the printed circuit board on the back of the instrument cluster was bad on mine causing both alts to never start charging. That new PCB and replacing some burnt out fusable links made a world of difference for my electrical system.

 

[Guyfang]

Anytime you have a problem like this, you need to unhook both batteries. Hook them up to a GOOD, SMART battery charger, and let them be fully charged. Then load test the batteries. Only then, will you know if the batteries are good. You are assuming, hoping that they are good. But you kneed to KNOW. If you do not have a good charger and battery load tester, borrow them and or take the batteries to a professional.

 

[Joey7]

I would study the exciter circuit for the alternators before assuming both are bad. I had thought the same thing till I looked in to how that circuit runs thanks to some advice from the SS forum. Turned out the printed circuit board on the back of the instrument cluster was bad on mine causing both alts to never start charging. That new PCB and replacing some burnt out fusable links made a world of difference for my electrical system.

I'm not great with electrical, mostly learning as I go. So what does the exciter circuit do? And how would I test it? When I get home today I'll retest everything. But the fact one batteries staying at 12.6v while running and the other draining immediately is what's throwing me off.

The battery that's staying at 12.6 while running is completely new, and the other is a little older but was holding full voltage before putting it in. But that's why I'm thinking there's a parasitic draw somewhere on top of a charging system issue

 

[GunnyM1009]

I'm not great with electrical, mostly learning as I go. So what does the exciter circuit do? And how would I test it? When I get home today I'll retest everything. But the fact one batteries staying at 12.6v while running and the other draining immediately is what's throwing me off.

The battery that's staying at 12.6 while running is completely new, and the other is a little older but was holding full voltage before putting it in. But that's why I'm thinking there's a parasitic draw somewhere on top of a charging system issue

I would do a horrible job explaining it but this is an article on here for trouble shooting the circuit. https://www.steelsoldiers.com/threads/cucv-gen1-and-gen2-exciter-circuit-troubleshooting.121589/
If the front battery is draining and the rear is staying constant it could just be that the rear is only used for the starter and your glow plugs. The entire 12v side of the truck runs off the front battery.

 

[cucvrus]

The batteries need load tested.
This is a chart showing what a battery condition is. And this indicates after being load tested. Good Luck. I know a lot of people don't like it when I say the battery is bad even with a 12 volt reading. It is the amperage that does the trick. Good Luck.

 

[Keith_J]

Original 27SI alternators have 4 required connections. These are battery positive, battery negative, voltage sense and exciter-trouble light.

On the driver side alternator, there is a brown wire that presses on a 3/32" smooth stud, about 5/16" long. This is for tachometer reading using military standard test equipment. The battery negative wire is black and connects to a manifold stud which is grounded so it goes to the front battery negative. The red wire connects to the front battery positive, through the front battery positive to rear battery negative. It has fusible link protection so if the red terminal does not have front battery voltage, check the fusible link. On the side of the alternator is a two wire plug with a brown and red wire. The red wire is voltage sense, it is protected by a fusible link so if does not have front battery voltage, check the link. The brown wire is excite-trouble light. Switched 12 volts with key on, engine off, is sent to the excite portion of the regulator. With engine off, the alternator is not making any current which means enough current flows through the trouble light to male it illuminate. Once running and generating current, the alternator internal voltage is greater than that supplied through the trouble light, causing the light to go out.

So, to test if it is the alternator or the wiring, measure voltages with key on, engine off. Driver side alternator must have front battery voltage on the big red wire and both sense and excite wires.

The passenger alternator is similar, only the voltages are measured using the back battery negative for the black lead of the voltmeter. The alternator negative is red with a black stripe and since it connects to both the rear battery negative and front battery positive, it will have front battery voltage to ground. And it is fusible link protected.

One other addition to the passenger alternator is a relay under the dash for excite wire. This shouldn't be an issue unless the vehicle has been dunked.

Make certain the wiring is stock, a few have tried to convert to 12 volt which leads to frustration. And get the technical manuals.

 

[Joey7]

Original 27SI alternators have 4 required connections. These are battery positive, battery negative, voltage sense and exciter-trouble light.

On the driver side alternator, there is a brown wire that presses on a 3/32" smooth stud, about 5/16" long. This is for tachometer reading using military standard test equipment. The battery negative wire is black and connects to a manifold stud which is grounded so it goes to the front battery negative. The red wire connects to the front battery positive, through the front battery positive to rear battery negative. It has fusible link protection so if the red terminal does not have front battery voltage, check the fusible link. On the side of the alternator is a two wire plug with a brown and red wire. The red wire is voltage sense, it is protected by a fusible link so if does not have front battery voltage, check the link. The brown wire is excite-trouble light. Switched 12 volts with key on, engine off, is sent to the excite portion of the regulator. With engine off, the alternator is not making any current which means enough current flows through the trouble light to male it illuminate. Once running and generating current, the alternator internal voltage is greater than that supplied through the trouble light, causing the light to go out.

So, to test if it is the alternator or the wiring, measure voltages with key on, engine off. Driver side alternator must have front battery voltage on the big red wire and both sense and excite wires.

The passenger alternator is similar, only the voltages are measured using the back battery negative for the black lead of the voltmeter. The alternator negative is red with a black stripe and since it connects to both the rear battery negative and front battery positive, it will have front battery voltage to ground. And it is fusible link protected.

One other addition to the passenger alternator is a relay under the dash for excite wire. This shouldn't be an issue unless the vehicle has been dunked.

Make certain the wiring is stock, a few have tried to convert to 12 volt which leads to frustration. And get the technical manuals.

Okay so everything looks stock to me. But both alternators have ground, as well as reading voltage. It might be worth mentioning I couldn't ever get a tach to work with that tach wire, so I put in a w terminal and couldn't get that to work either. I'm re testing everything now. Is there anything I should check aides from batteries, and alternator connections? As far as I can tell everything looks normal. And I'm fairly certain this is more than a battery issue

Driver alternator
Key on engine off :
11.79v main power
11.77 red wire
Brown 0.07

Key off:
Main power 11.9
Red 11.94
Brown 0

Passenger
I'm getting ground out of both wires coming out of the plug.
Key off:
main power 24.8
Lower red plug 12v

Key on engine off:
Main 24.5
Lower plug 11.8

 

[Joey7]

Original 27SI alternators have 4 required connections. These are battery positive, battery negative, voltage sense and exciter-trouble light.

On the driver side alternator, there is a brown wire that presses on a 3/32" smooth stud, about 5/16" long. This is for tachometer reading using military standard test equipment. The battery negative wire is black and connects to a manifold stud which is grounded so it goes to the front battery negative. The red wire connects to the front battery positive, through the front battery positive to rear battery negative. It has fusible link protection so if the red terminal does not have front battery voltage, check the fusible link. On the side of the alternator is a two wire plug with a brown and red wire. The red wire is voltage sense, it is protected by a fusible link so if does not have front battery voltage, check the link. The brown wire is excite-trouble light. Switched 12 volts with key on, engine off, is sent to the excite portion of the regulator. With engine off, the alternator is not making any current which means enough current flows through the trouble light to male it illuminate. Once running and generating current, the alternator internal voltage is greater than that supplied through the trouble light, causing the light to go out.

So, to test if it is the alternator or the wiring, measure voltages with key on, engine off. Driver side alternator must have front battery voltage on the big red wire and both sense and excite wires.

The passenger alternator is similar, only the voltages are measured using the back battery negative for the black lead of the voltmeter. The alternator negative is red with a black stripe and since it connects to both the rear battery negative and front battery positive, it will have front battery voltage to ground. And it is fusible link protected.

One other addition to the passenger alternator is a relay under the dash for excite wire. This shouldn't be an issue unless the vehicle has been dunked.

Make certain the wiring is stock, a few have tried to convert to 12 volt which leads to frustration. And get the technical manuals.

And I forgot to add, I definitely think somethings going on with the charging system, but when one battery was reading a bit over 12 and the other was 11.8, I wasn't getting a crank, and hardly any power in the cab. After a few seconds holding the golowplugs it sounded like a relay ran out of juice. And the other day I managed to jump it, started driving and after a few minutes a lost power to my stereo, blinkers, lights, ect. I don't know if there's anything powering the main fuse box, and ignition but that almost seems like the problem

 

[Squibbly]

I'd start with a good baseline.
Go get a battery load tester as @cucvrus suggested:

...or take all of your batteries to AutoZone or NAPA or one of those places, and they will not only load test your batteries, but will check your generators for free.

If you aren't 100% sure your batteries are good (which you can't generally do without a load test), then you can spend weeks troubleshooting something that could have been solved in 5 minutes.

If everything checks out on that front, then we can start going down the troubleshooting flowchart, but you're going to potentially waste a lot of time skipping that first step.

 

[Guyfang]

Joey, Have you noticed yet, that everyone has said you need a battery load test. For this kind of problem, you need to troubleshoot the problem in a Logical method. You start at the beginning, and work from there. Every time you solve a problem, or prove something is good, you are closer to finding the problem.

 

[Joey7]

Joey, Have you noticed yet, that everyone has said you need a battery load test. For this kind of problem, you need to troubleshoot the problem in a Logical method. You start at the beginning, and work from there. Every time you solve a problem, or prove something is good, you are closer to finding the problem.

Yeah and I did get a load test and one was going bad. So I put a brand new one in with the same problem, and my other battery was reading like 7v, so I put in another 650 for testing. Yes, the cca is way too low but it was all for testing. I'm gonna get them load tested again today to play it safe and in case something went wrong last time

 

[Joey7]

I'd start with a good baseline.
Go get a battery load tester as @cucvrus suggested:

...or take all of your batteries to AutoZone or NAPA or one of those places, and they will not only load test your batteries, but will check your generators for free.

If you aren't 100% sure your batteries are good (which you can't generally do without a load test), then you can spend weeks troubleshooting something that could have been solved in 5 minutes.

If everything checks out on that front, then we can start going down the troubleshooting flowchart, but you're going to potentially waste a lot of time skipping that first step.

Yeah I got my original ones tested but not the ones I currently have in there. So I'm just gonna get everything load tested one more time and hope thats the problem

 

[Mullaney]

Yeah and I did get a load test and one was going bad. So I put a brand new one in with the same problem, and my other battery was reading like 7v, so I put in another 650 for testing. Yes, the cca is way too low but it was all for testing. I'm gonna get them load tested again today to play it safe and in case something went wrong last time

.
A matched pair is a good way to install batteries.

 

[Guyfang]

Charge them with a GOOD, smart Charger first. Then load test.

 

[Joey7]

Okay so batteries tested good. Truck was running fine today. I disconnected a handful of stuff I wired a few days ago, but both batteries were staying around 12.6v. a day or two ago my front battery was dropping .1v a second after start up. I was trying to get my generators testing too but after taking them both out in the Napa parking lot they told me they couldn't get a reading out of them. So I'm gonna take them to a alternator rebuild shop and have them tested if the problem occurs again. Usually after fully charging my batteries everything runs perfect for a couple days before everything starts to act weird

 

[Keith_J]

Ok, sounds like exciter circuit problems on both alternators. You need to trace the wires from engine side to the generator lights in the dash.
The light bulbs must illuminate with key on, engine off. The current illuminating the bulbs bootstraps each alternator, providing current to the rotor through the slip rings. This turns the rotor into an electromagnet, it spinning in the field coils generates AC power. A tiny bit of the field AC is turned into DC by the diode trio. This direct current feeds into the excite terminal, once the diode trio voltage exceeds the excite voltage, current through the generator light bulb stops.

 

[Keith_J]

The negative is isolated from the case, unlike most other alternators. So if the tech didn't bond the negative to the case, the alternators would fail the test.