M923a1 alternator voltage gauge readings

[diverman555]

Hey Dukeman, what is the reason for your question? Is your Alternator not working? Is the gauge not showing charge? what is the problem.

 

[Dukeman]

My issue is exactly what you described in your original post. Meter in the yellow, only charging 24.5 volts across the batteries. Let me tell you what I did this weekend though. I removed the existing batteries and replaced them with two brand new Interstates that I had just put in my F350. I thought maybe the existing batteries were not holding a charge or just needed to be replaced. There was no difference in the voltage output of the alternator. I did the step by step alternator check procedure shown in the PS article I think on the first page of this thread and verified only 24.5 volts directly from the alternator connections. So it seems like we need a new alternator, but. Went and took a drive about 14 miles and at about the 10 mile mark the voltage gauge moves in to the green. I get it back home and verify 29.6 volts at the batteries, whoa! So I pull the plug on the alternator and adjust back to 28 volts, perfect. So I don't know if maybe the regulator has a bad connection somewhere or what, but maybe it just needs to be driven. It has sat for about a year. We drove it 60 miles home and within about 30 miles the voltage meter climbed in to the green just like it did yesterday, so we figured everything was ok. So I guess I will drive it some more and see what happens. I just hate to spend $64 on a new voltage regulator and find out that isn't the problem.

 

[maccus]

The regulator is bad. You have described one possible failure mode exactly the way one will see it when the regulator fails.

 

[Dukeman]

Thanks Maccus, kind of what I was thinking. I went ahead and ordered a regulator this morning.

 

[maccus]

Wise decision. You would have risked damaging your new batteries were you to have driven the truck for any length of time with that particular problem in the regulator. And as we all know batteries are getting to be a major expense. Especially if your truck were to have needed 4 batteries like the 5 tons do. I have purchased good MVs for less than they want for four of the new gel style mil batteries.

 

[Dukeman]

well, I should have known better. Got the new regulator and went to install it. When I got the alternator out and took the old regulator off it was completely fried. I mean melted. I should have know better then to try a new regulator, but I figured it was worth a shot. Cleaned out all the goop and installed the new regulator, put everything back together and started her up. Worked great for about 15 minutes. Then it went in to the red and started over charging to about 30 volts. I couldn't adjust it at all. So I think there was probably a problem with the alternator to begin with and that's what fried the original regulator. Now I'm probably out the $70 I paid for the regulator and need a new alternator. Has anyone used the Spider Marine Alternator? What modifications are required to set it up?

 

[ChuckM]

I replied earlier to go straight for the 21si. They work great and it's the the only way to go if you are having alternator trouble. You are going to have to modify the bracket and pulley to make it work.

 

[Dukeman]

Hey Chuck, no problem with the bracket, what about the wiring. The small wire how does that hook up. And the pulley, can you just use the pulley off the original alternator or do you need a new pulley?

 

[ChuckM]

I didn't use the original wires to the alternator. I taped them off and ran a new positive wire to the batteries. I also ran a ground wire from the alt to the batteries. The new alternator will come with a simple wiring diagram. The pulley will need to be drilled to 7/8".

 

[Dukeman]

So the small wire that comes off the original alternator that goes to the ignition switch is just hooked to a positive terminal right? So that wire could go to the same post as the positive battery cable?

 

[ChuckM]

Yes and yes. I wanted new wiring directly to the battery to eliminate anymore possible issues.

 

[Dukeman]

Thanks Chuck, yeah I kind of figured it out. Found this:

http://www.newindo.com/pdf/1G286.pdf

Goes in to a lot more detail about the alternator. You might be interested in it.

 

[Dukeman]

Okay, got the new alternator in. Worked out great. Got the old pulley off and drilled it out to 7/8". Thanks Chuck for that measurement. Wound up just putting a 2" piece of pipe as a spacer on the back of the alternator to tie in to the lower bolt hole on the existing bracket. Very solid set up. I hooked up the existing positive (#5) to + on the alternator and the existing negative wire (#3) to - on the alternator. I hooked #566 to ignition on the alternator. There is one wire left, the wire with the connection on it that is hard wired to the old alternator #568. The wiring diagram in the TM shows 568 going to the control box. But the wiring diagram also shows #566 going to the control box, I thought that was the ignition wire? Anyway, everything seems to work fine, the wiring diagram does not show any voltage, so I don't know if I should hook #568 to a 24V lead on the alternator or just leave it unconnected. I see all these wires going in to the control box, but can't tell what they do after that.

 

[dconradb]

Hey Dukeman, what is the reason for your question? Is your Alternator not working? Is the gauge not showing charge? what is the problem.

A while back you had a problem starting your m923, you had power to the battery switch but no power to the starter switch. what was the fix and did you ever find a wire diagram for your m923 ? my truck has the same problem now, can you help ? THANKS

 

[Dukeman]

Diverman said he wound up putting a new regulator on his alternator. That must have fixed the problem for him. Wiring diagrams are in the TM section, appendix H.

 

[diverman555]

Ended up that all was well, the paint on the back of the panel was keeping it from grounding. Cleaned the paint off and got it to ground and it worked fine. Both trucks were the same.
So start with the simple things.
Mark

 

[diverman555]

simple things

Ended up that all was well, the paint on the back of the panel was keeping it from grounding. Cleaned the paint off and got it to ground and it worked fine. Both trucks were the same.
So start with the simple things.
Mark

 

[rickycotte]

Diverman said he wound up putting a new regulator on his alternator. That must have fixed the problem for him. Wiring diagrams are in the TM section, appendix H.

Hi everyone. I am amazed about coincidences or this equipment is junk. I have been working for two days now on a M931A1 with the yellow range in the voltmeter syndrome.

I did get info from the TM...just in case. I have been recharging the batteries one at a time since all I got at the time is a 12V charger. So, this takes time and it is a pain in the lower back. I could not imagine why someone figured to install these batteries under the bench seat. It is really hard getting up and down sooo many times on that passenger side. But I digress.

I am very happy of having found this thread since I got ample info on my alternator problem. I did all the tests (specially test #14 Alternator adjustment) and am getting only 24 volts. This means the alternator at least is putting out voltage.

The problem is that darn adjustment screw underneath the pipe plug. As Dukeman says, it is impossible to look at it because part of the engine cooling system sits on top of it. I did not know it was a Philips!! The TM shows what it looks as a regular slot. So much for the TM.

I will look tomorrow for it but most surely will not have any effect as you guys say. Maybe the regulator is toast.

Thanks to all for the info.

 

[juanprado]

For whatever you think this is worth....

I sold parts for 20 years and I always recommended to replace an alternator with a built in regulator whenever there was a problem. The internals are just as old as the regulator, even more so if it was a reman and all subject to wear. Electrical gremlins that kill the regulator can also fry other gizmos. Sure you can go cheap and replace a regulator, brg, diode, etc but you will be back at is soon enough when the next component breaks, wears out etc. Time after time, Murphy proved this scenario to be accurate.

More $ on the front end but no hassle, down time, break down etc

Yes, I know the regulator is just mounted externally and not literately internal but in this case; same idea.

Happy Amping and Volting down the road.

 

[rickycotte]

Okay, got the new alternator in. Worked out great. Got the old pulley off and drilled it out to 7/8". Thanks Chuck for that measurement. Wound up just putting a 2" piece of pipe as a spacer on the back of the alternator to tie in to the lower bolt hole on the existing bracket. Very solid set up. I hooked up the existing positive (#5) to + on the alternator and the existing negative wire (#3) to - on the alternator. I hooked #566 to ignition on the alternator. There is one wire left, the wire with the connection on it that is hard wired to the old alternator #568. The wiring diagram in the TM shows 568 going to the control box. But the wiring diagram also shows #566 going to the control box, I thought that was the ignition wire? Anyway, everything seems to work fine, the wiring diagram does not show any voltage, so I don't know if I should hook #568 to a 24V lead on the alternator or just leave it unconnected. I see all these wires going in to the control box, but can't tell what they do after that.

From what I have researched, #566 prevents the starter from being engage while the engine is running. It seems this wire delivers whatever signal (voltage, freq.) to the protective control box (mysterious black box by the drivers side firewall) for this.

9 CIRCUIT 566 - Controls a relay in protective control box that prevents starter from reactivating</SPAN>
while engine is running.