The only gauge that will work after converting your electrical system to 12 VDC will be your oil pressure gauge as it is a mechanical gauge.
I thought all the guages in the M715 were electrical. Hence being Mil Standard?
I know my 715 was in fact I took the gagues out of my m151 and used them in the 715 for testing so that I could figure out which ones were good and or bad. Did I miss something along the way?