M923a1 alternator voltage gauge readings

[diverman555]

I put a rebuilt alternator on my M923A1 it did not have one. On the bench the alt read 24.3 volts, put it in the truck and looked at the gauge and it showed in the yellow about the middle. Well knowing what the alt was on the bench I just ran it in the truck for a few weeks. Truck ran fine, never had any issues, even running full lights. I tested power at the batteries and same readings 24.3 pulled the gauge panel out and pulled the single wire that goes to the gauge and tested it there and it was 24.3 So I figured it must be the gauge so I bought a new one, not used.
Installed the new gauge started the truck, and the needle went right to the middle of the yellow. So volts read 24.3 at the alt, the batteries, and at the gauge, but the gauges still show middle of the yellow. Looked at the TM's and they showed to check everything that I checked. Has anyone ever heard of this where it is showing the correct volts even at the gauge wire but still shows low charging at the gauge.
Thank you for any help.
Mark

 

[dozer1]

Could that gauge need a better ground to the truck? Maybe there is some resistance on the ground side of things making it read lower then it should. Also if you bench test the gauge on a known 24 volt source, does it read higher ?

 

[phil2968]

24 volts is not enough. You should be around 28 when running. The alt is not making enough volts.

 

[MidNightRider]

I agree with phil2968, you need to adjust the alt. if it is the standard 60 amp alt, you need to go to the regulator on the back of the unit, look for a small allen head screw near where the wiring is going into the unit, remove the allen head screw, insert a small phillips head screwdriver and turn the adjuster right or left, if you hook a multimeter at the alt wiring, you can watch the readings as you turn the adjuster, we always adjusted them to 27.8 volts, and then just reinstall the allen head plug and you are done.

 

[cranetruck]

Right, adjust output to 28 plus a fraction.
The gauge showing in the "middle of the yellow" would be about right for 24.3 volts, nothing wrong with the gauge (see image).

 

[cranetruck]

Here is a PS magazine procedure, note the desired 28.5 adjustment, about 14.2 V across each battery.

 

[diverman555]

I Did pull the little plug and turned the screw under it counter clock wise which the TM shows to increase voltage. the screw only turned about 1/4 turn. I did not have the use of a volt meter at that time so I don't know what exactly the voltage reads now, but the screw is all the way up, or to the left, and the volt meter is still in the yellow.
I am going to put a pic up of the little analog meter I have. Let me know if this is a good unough meter. I will post in a minute

 

[diverman555]

Here is a pic of my meter

 

[MidNightRider]

i have used that type before and had no problem with it. but you said you have tried to adjust it, all the way left & right and nothing happened? so you are saying that the voltage did not decrease? it just stayed at 24? something does not sound right.

 

[MidNightRider]

ok, you said rebuilt alt, i thing you might want to see if you can get anothr regulator for it. it sounds like the alt is working as you stated that it does charge to 24 volts, but it sound like you need a new regulator so you can adjust it to 28 volts. just my 2 cents.

 

[diverman555]

I might not have explained that good enough. I took the cover off, took the plug out, but I did not have a volt meter at the time, so in the tm's it says counter clock wise to increase voltage. So I turned the screw counter clock wise but it would only turn about 1/4 turn. Since I did not have the meter I just looked at the truck volt meter and it was still in the same place. I have my meter back now so I can check just what the voltage is when it stops raining.

 

[diverman555]

can you buy just the regulator for that? well I would guess you can. I will check with the shop and have them order one. Never thought that just the regulator could be bad.
Thank you.
Mark

 

[gringeltaube]

NO, DON'T read the TM (in this case)...
just re-read posts #3 to #6 again and again...! Maybe then you will understand that for doing this right you'll need to get a (accurate)voltmeter and hook it up between alt. output terminal and ground...

With engine at idle adjust to 28.0V - 28.2V.
Repair/replace alternator if you can't get that voltage!

G.

 

[ChuckM]

Make sure you are getting battery voltage to the exciter wire when the ignition switch is on.

 

[M923driver]

If you can't adjust it any higher, your rebuilt alt might need a rebuild. Try moving the screw in and out, it may have some corrosion or other thread issues. I've had rebuilds that had issues right out of the box, not too uncommon.

 

[ChuckM]

can you buy just the regulator for that? well I would guess you can. I will check with the shop and have them order one. Never thought that just the regulator could be bad.
Thank you.
Mark

I was having an overcharging issue last week and put a new regulator ($63) from Erik's on mine. It would charge fine for about 5 minutes and then start overcharging...even rewired straight to the batteries. So a new regulator is not a guarantee fix. I dislike spending money with negative results. I ended up buying a delco 21si ($110) from spidermarine. Problem solved!! Do a search for this upgrade or pm me for more details.

Regards,
Chuck

 

[73m819]

Another GREAT THREAD title (Please don't say read the TM's) to help in search for help with alt. problems,

 

[197thhhc]

I am a huge fan of upgrading to the delco alternator. 1 wire no issues.

 

[gimpyrobb]

Read the TM!

 

[TIGERFANS2]

and get thee down to harbor freight and buy their el cheapo (~ $5.00 ) digital voltmeter ,
they aren't HP's but most are pretty close, closer than trying to read that analog