Sense wire for alternator

I recently upgraded to a denso alt, ever since I did I noticed my interior light would flicker at idle and a relay would click in my dash. Turned out the relay was for my vintage air, I checked volts at the relay and it was spiking to 15 volts.
I checked volts at my electric fan and same thing. Spiking so fast my volt gauge wouldn't register it.
After running a bunch of extra grounds, changing regulator I tried changing the point of my sensing wire, as it turns out if I use any keyed wire I get a spiking condition. If I hook it to a continuous supply it works fine.
This has me baffled