Alternator charge

I'm not familiar with every set up, but that seems on the low side to me. Where are you taking your readings while running, the back of the alternator, or at the batteries?

 

Shouldn't it be around 14.6 volts?

 

That is ideal but should be at least 12.8 and no more than 14.8 I would not trust what the truck is telling you put a good meter on the batts. A fully charged battery is 12.6 volts. You should check voltage with the truck running and everything on (lights, ac, blower fan everything you can turn on) If you have 13 volts I would not bother with it.

 

I had kinda the same problem on a Volvo 780..The alternator was 5 years old so I changed it and the local electric rebuild shop put an external wire for the regulator...I had to run a wire for the alternator to the battery so now the alternator regulator senses battery voltage rather than alternator output...Holds the batterys at 13.8 to 14.0 VDC....

 

best thing to do is get a digital multimeter and check it out ground the neg lead and put the pos lead on the pos output of the alternator see what your reading is then go to your batteries and ground the neg lead and hit the pos to the pos post of the batt see if there is a resistance in there there shold be no more than .02 volt between teh alt and the batts if more than that then chances are you have loose or coroded connections somewhere voltage should be between 14 and 14.8 no higher than that though when running when the engine isnt runnin it will be around 12.8 anything passed 12.2 batts prolly dead

 

A 24V system on a highway truck is very unusual these days... are you sure the batteries don't connect somewhere after the battery box?

The last 24v system I had was on a 70's vintage Freightliner...

 

there are no trucks other than military built after 86 that are 24 volt...