I was trying to help my dad with his car yesterday, and found I didn't know much. He has a '40 Ford coupe with a 6/12 volt system. 2-6 volt batteries with some systems in series and some in parallel. He has installed a 12 volt tach and I believe the feed is one keyed hot (6 volt), one battery hot (I'm pretty sure it's 12 volt), a coil feed and a feed for the light. He bought a tach that reads pulley rotations and we found that the mounted tach in the car is reading double what the hand held one is. My hope is that by changing the battery hot to 6 volts, the mounted tach will read true. Or, does he need a 6 volt tach? Above my pay grade

Dave, Kamloops, B.C. '65Crown V8, 2009 Tacoma

Does the tach have a 4-6-8 switch that could be used to advantage?

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
65 Canadian Monza 4dr 110/PG 40k
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

Ya, for sure Craig. My Dad had it set for 4 cyl. and it was at 2200 at idle and after we switched, it was 1100. Closer, but still double the actual idle speed. He said he will try switching the one lead from the battery to 6 volt today. I will check back with him later today. Cheers, Dave