Wiring in a Rev Counter

[P1800Ray]

I acquired an unfitted aftermarket rev counter when I got my Amazon. I’ve tested it and it reacts when connected to the battery.

How would this be installed? In addition to the red and black cables there are green and white ones.
Thanks

[Ron Kwas]

Ray;

"reacts when connected to the battery.", is reaction associated with smoke?...not so good, or simply a minor needle bounce, and not much more? ... and wire color codes...are not really enough, because there is little standardization...first thing I'd try is to get a manufacturer's name and product ID from it and see what a Gargle search comes up with...

If you insist on a trial-by-fire (potentially!) method, connect power to Red and Blk (1A fuse is highly recommended!) connect green wire to 12V, by way of a 10-100Ohm resistor, and see if it lights an internal instrument lighting lamp...White might be Ignition signal input...momentarily test-connect to points wire of the car (engine running), and see if instrument reads anything useful...

Use these hints at your own risk... again, I'd much prefer working from a definite wiring diagram...but if I was on a desert island, and had to figure connections out the hard way, and as an electronic guy, before connecting, I'd take the instrument apart and inspect where wires go internally...I can learn much from this toward correct hook-up, but it does you little good...

...hope this helps, just a little...

Good Hunting!

[Derek UK]

What make of tach? TIM, Yazaki, Smiths? Google that make tach and wiring diagram. Or Google wiring up a rev counter and go to images. See if you can find yours. They are all pretty similar and will probably involve the low tension wire on your distributor.

[Laird Scooby]

I've had a few aftermarket tachos over the years and the wiring was always :

Red +ve 12V ignition fed
Black 0V -ve/earth
Green signal input from coil - terminal
White sidelights circuit

However, to be sure, i'd suggest you get a multimeter and put it on resistance and check the resistance between white and black, if it's in the region of 50-120 ohms, chances are it's the lighting circuit. Holding the black on the -ve battery terminal and a very quick flick of the white one onto the +ve terminal should see some light inside. By light, i don't mean a blue flash, i mean a bulb lighting up.

If so (or no light at all because the bulb has blown, give those connections above a try. You may also find if it's one of the bigger ones designed as a stand-alone unit with a bracket to scrw it to the dash or similar, there is probably a screw or two in the back and you can remove and see where the wiring goes.

That would confirm the white as being lighting and give you a chance to renew the bulb too!

You may also find there is a switch inside to select 4-6-8 cylinders, set it to 4 unless you've done an engnie swap for something bigger than Volvo fitted! :thumbs_up:

[P1800Ray]

It’s an Equus. No obvious model number but I’ll have a look tomorrow.

[P1800Ray]

Ron, I just tapped it on a leisure battery that I have rather than connect it up in the car.

[Laird Scooby]

It’s an Equus. No obvious model number but I’ll have a look tomorrow.

https://www.iequus.com/pub/media/manuals/Tachometer.pdf

In that pdf, scroll down and you'll find the colours in a diagram, exactly as i suggested. :thumbs_up: