Hitman's Pontiac Trans Am Forum

Trans Am Information => Trans Am Tech => Electrical => Topic started by: KJMason on September 16, 2014, 10:04:36 PM

Title: '71 Points Tachometer with HEI
Post by: KJMason on September 16, 2014, 10:04:36 PM

My '71 TA has the original gauges with the single wire tach; however a PO replaced the points distributor with a later model GM HEI. My tach is correctly connected to the HEI with no filters or resisters in the circuit. It operates correctly but reads about 25% low (shows 750 at 1000 RPM and 1500 @ 2000rpm, etc.  I've read that GM changed to a different tach that had a +12V input in addition to the tach trigger wire when they began using the HEI and was wondering if anyone knew of an adaptor, filter, or modification that would fix this (short of replacing the tach that is.)

Thanks,
Kevin