Corey 12 Posted March 26, 2014 G'day everyone, I want to install a tacho into my 85 F100, it never had one in the past as far as I can tell and I don't know anything about how these work, I've never had to install one previously, will the motor already have a sender or something in it or will I have to buy one to suit? It's a 351c if anyone can help me with this that'd be great. Cheers, Corey Share this post Link to post Share on other sites
gerg 10,871 Posted March 26, 2014 A tacho just counts the ignition pulses coming from your coil. Aftermarket tachos often come with a switch on the back that goes from 4-6-8 cyl, so are universal to some extent. They need about 4 wires normally, one from neg side of the coil, one from ignition, an earth, and a tee off from your dashboard lights if they come with a built-in backlight. For simplicity, you could just loop the power for the lamp around from the wire from ignition so it's on all the time.<br /><br />Factory ones are often purpose built for the engine, unless you want to tinker with a 6 cyl one to make it work with a V8 like I did... Got it to within 50 rpm accuracy by guessing! 1 Corey reacted to this Share this post Link to post Share on other sites
Corey 12 Posted March 26, 2014 Exactly what I was after, thanks mate! Bit annoyed I never learnt about these before, it seems so simple now. Share this post Link to post Share on other sites
Outback Jack 6,352 Posted March 26, 2014 Usually when ya buy a tacho, theres a wiring diagram in the box, should be pretty easy to fit to a 85 Effy. Jack. Share this post Link to post Share on other sites
gerg 10,871 Posted March 26, 2014 Exactly what I was after, thanks mate! Bit annoyed I never learnt about these before, it seems so simple now. There is kind of a "sender" for a tacho, but they are for diesels which have no ignition pulses. They take the AC frequency output of the alternator before it gets converted to DC and calibrate the tacho to that. Share this post Link to post Share on other sites
