Sense wire for alternator

[11.2]

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

 

[KitCarlson]

The regulator controls the field current to regulate alternator output voltage. The IGN terminal as you know is the sense point. The regulator nominally attempts to keep IGN at 13.8V, but it will be slightly higher when temperatures are cold, to more correctly fit the charge requirement of battery. The alternator is electrically closer to battery, and voltage drop between battery and IGN increases battery voltage by that undesirable amount. The drops in the path typically include battery to starter relay stud, fusible link, bulkhead terminal, ignition switch, bulkhead terminal, IGN circuit. You can easily measure the drop, voltmeter IGN to battery terminal. Fix drops, eliminate regulator over voltage.

 

[11.2]

When I use an ignition wire it runs 14.7 - 15.0 volts. When u use a battery wire it runs a steady 14.7.
The reg is brand new but I think I'll try another one. I doubt 15 volts would hurt anything but it's enough to make my ac relay go stupid.

 

[KitCarlson]

Read the voltage at IGN, is it steady? If so, regulator is working fine.

Varying load on IGN, from ignition may result in some transient behavior. If you have other loads there, that. Is a problem too. Loads should feed off ACC, and relays for large load. The IGN circuit has skinny wire.

Have you measured 0.3V variations from battery to IGN?