Chronic Overcharging Issue

Hello all. For the last 7 months i’ve been having charging issues. Not undercharging, overcharging. Bad overcharging. Today it clocked in at 17.5v. I’ve replaced the 120 fuse multiple times because it keeps melting on the battery connection side. I’ve replaced the alternator voltage regulator, and the battery, and the alternator once. With a new alternator it wont charge at all. I’ve resurfaced connections, cleaned them, etc, they’re all tight and strong, ive changed fuses maintaining therated amperage, and at this point I’m stumped. Sometimes its fine, rests happily at 14.7 volts. Then all of a sudden it wants to fly to 17.5. Highest its gone is 19.2. It’s a Denso alternator with an OEM regulator. The pigtail harness for the alternator is new and the wiring is new. Does anybody know what course of action i should take next, comments, questions, etc? I’m completely stumped. And at this point its blowing fuses every time i run her. It used to not charge at all and now just charges to the moon.

 

Do you have a diode in the ALT-S fuse location? This is required for AGM batteries.

 

Only thing I’ve seen/heard relating to this is a bad alternator ground.

 

I have a fuse(pretty sure that’s a diode?)in there, a 7.5 amp

 

Test the battery to make sure it's still good? All those voltage spikes aren't exactly good for the battery. Usually any time the voltage spikes high it's the voltage regulator, or it could be a dead cell in the battery causing a larger draw from the alternator.

Here's another thread with the same problem.
https://www.tundras.com/threads/power-surging-alt-putting-out-18-volts.88881/

 

I didn’t think of that. I’ll go clean that up and try again in the morning.

 

if I recall, ALT-S if containing a diode, amplifies voltage to be compatible with AGM. But I can’t remember. There is info about it on this forum.