I've tried an adjustable regulator for my IVR, adjusted it to 6.0 v and it was not right. I then readjusted it to 5.0 volts and it seemed to be much more accurate.
If you ever took apart a OEM voltage regulator, it is nothing more than a fast acting flasher. It turns on and off very fast and lets the capacitor smooth out the voltage. a very antiquated PWM type system.
On my modification. I have tuned the voltage regulator and it is running like new. At this point I am not going to disassemble the cluster to see what voltage that is.
