Join Date: Dec 2002
Location: Saint Louis, Missouri
Re: Recommend + and- for tach
What brand and model tach ?. Is there a link to the wiring diagram ?
On most basic tach installs, I would make the connections for power and illumination to the fuse block. I would also find out if the manufacturer recommends any kind of inline fusing on either or both of the power wire and illumination wire.
In the middle of the factory fuse block, there are 1/4" male terminals that allow accessories like a tach, aftermarket radio, aftermarket gauges, and such to get different types of power for them such as a constant 12 volts, an accessory 12 volts, an ignition 12 volts, and an illumination 12 volts that comes on when the parking lights are on and is also dimmable. I would power the tach off of the accessory or ignition (marked ACC or IGN on the fuse block) 12 volt terminal in the fuse block, connect up the tach's illumination wire to the LPS terminal on the fuse block, then ground the tach to either an existing firewall bolt or find a good metal spot on the firewall to connect to solidly. For the signal wire that would connect to either the coils negative terminal on a normal points ignition or to the HEI's TACH, use an existing hole in the firewall that has a rubber grommet in it.
If the manufacturer suggests something like a 10A fuse, put this fuse close to the fuse block so that if the wire ever gets shorted past it, the fuse will blow. Also crimp on a ground ring terminal to the tach's ground wire and don't just wrap it around or under a bolt.
1974 Spirit Of America Nova (being restored), 1973 Nova Custom, 1968 Chevy II (Garage Find 2012)
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