740 New to me 740 overcharging

Just picked up this new 740 turbo wagon. Had to get a battery when I picked it up too. Came home and tested her with a multimeter and she was showing 16.50! Spiking upto 18 next day. So today I just swapped in am old regulator I had in a 740nalternator I had sitting around. This regulator had less life on the rotors then the one I took out. At first she showed only 13.5 but then she jumped back upto 16 volts. Wondering if I should swap the whole alternator?

I thought this was regulator related. Or maybe a whole brand new regulator will do it? Or...! Is this connected to a rotten wiring harness and that's what can cause overcharging sometimes?

As is right now I took out my brand new battery and have my dead one in there and I jump the car to get going. Because I don't want to cook the new battery. But I'm also worried this could be harming other electronics

-jason
It's an 86' 745 turbo

Alternator's internal voltage regulator has probably failed. Time for a replacement alternator. More than just the battery will be damaged by overcharging. Headlight bulbs, windshield wiper motors, and radios don't like overcharging.

Hmm, that makes me wonder - my system runs 14.5 volts when the car is on. Is this overcharging as well?

No anything above 15-15.5 is overcharging really.

P.s- I ended up swapping the altnator itself with an old 74o turbo alt. I kept the regulator with the most life left on its brushes. I patched the bits of wire that had become bare going to the alternator. But yeah swapping alternator still has me at 16volts. Odd.. when the stores open next I will be getting a new voltage regulator. Let y'all know

Feel like such a tool. I did not know multimeter could be wrong. Not just not working. But it shows 2-3 volts higher over say 10 volts. I had tested it on a double a battery myself thinking that was a reliable test. But apparently on low voltages the multimeter shows the right voltage.