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Hi my name is Robert...
The only thing I can think of on this is if you have a battery isolator and it is faulty, the battery isolator will take the incoming voltage from the alternator and charge BOTH the chassis and house batteries. I would follow the cables from the alternator, most isolators have three posts, incoming from the alternator, outgoing to the chassis and house batteries, the voltage should be within one volt from the alternator input. If the voltage is good going into the isolator and low going out it is the problem. Also you might have a battery control box located outside, inside this box are some fuses, solenoids and auto breakers, if you happen to see that please get me the make and model of the box. The reason being is the charging may go through that box and it uses a printed circuit board....... Let me know if you need more help, I am around daily and respond when I can... Robert
I do not have any info on that box, what I might try and do is get a volt meter and with the engine running see if you can locate the alternator output on one of the soelnoids on the top, looks like you have three of them, I am not sure if they are using them for the charge circuit, my guess would be battery boost (which could be the charge solenoid), house battery disconnect and chassis battery disconnect, you should be able to hear them click when you hit the button inside for the boost disconnect etc, the problem could be in that box, it also looks like to me someone has rigged a jumper on one of them to bypass the solenoid, not sure what is going on there. Really need to follow the main cable off the alternator and see where is it going, in that box you also have two auto breakers to the right of the solenoids, make sure you have the same voltage to chassis ground on each post with the engine running.... Robert
At 1500 RPMS you should have close to or over 14 volts, I do not know that year if you have an external voltage regulator or it is built into the alternator, IF you had a external one it would be mounted to the chassis frame. I would see what you get at 1500 rpms, make sure the battery cables are clean and tight, looks like you just replaced the alternator and batteries so would be rare for an alternator not be working if it is new..... Robert
Hi was just checking in to see if my answer helped??? IF you have more questions or concerns please feel free to contact me....