Hey there. This car not charging well after warm up the engine. Few years ago change the alternator for same reason. But didn't solve the problem looks like..

Here is my check.

Start up engine. 14.45V from B at alternator. Regulator connector S (red wire) has 14.45V. Regulator connector F(yellow wire) has 14.40V.

After while start drop down voltage at B and connector F. 14.45 to 11.85V. After 20min later B 8.85V F 8.45V. Engine temp is operating temp. Outside temp 4C.

Also this RV using a Multi isolator. They have 4 pin.

At alternator from B to A(isolator) 1(isolator) to main Batt and starter. 2(isolator) to second Batt.

At alternator from S to 2(isolator). From F to R(isolator).


Please help is this alternator problem ore something else?

Thank you for your help

Do you know the type and model of the alternator? Is it a delco or denso or mitsu or some other brand.

If that's built on a GMC chassis, it should have a Delco alternator. Delco alternators have built in voltage regulators so if your output voltage goes low like you've described, the most likely culprit is the alternator. You can remove it for off-board testing to verify the fault at many parts stores.

Thank you guys its fixed, the RV has isolate. The iso late affected. One wire wet wrong spot. Now is OK.