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How to connect a 12 V tach.
Posted: Sat Sep 21, 2019 3:11 pm
by Boze
Just as an aside, is there an easy way to wire up a 12 vdc tach or should I look for a 24volt model. If so, who sells them? Understand that most of what was written above went zoom! right over my noggin!
Your post was actually hijacking Lyle's post and not at all related to mechanical tachs. I took the liberty of starting a thread for you here. Wes K. management
Posted: Sat Sep 21, 2019 10:42 pm
by wesk
As a rule electric tach's used with Pulse type ignition are the 3 wire type.
1 - Positive power wire is + system voltage. IE 6, 12 or 24V.
2 - Negative - ground wire grounds the tach to the vehicle.
3 - Brown sense wire senses the pulses at the coil negative - terminal.
A 12 volt electrical tach requires no more than 12-14 V's on it's + positive wire. So you could either place an inline resistor in whatever source wire you decide to power the tach to drop the voltage from 24-28 to 12-14. Or you could run a special wire from the 1st battery (on the M38 this is the under hood battery) to the + positive line on the tach. In either case that power source must be switchable on/off so as not to run the battery down when the engine isn't running.