Autometer Tach

[ricoc]

Ok so mine works on fours that have a distribrutor. Anyone have a trick to have the tach read twice the pulses. I have it working at half the correct RPM.

Our coils each spark once every RPM and the tach wants 2 pules/RPM

I think I will try two high value resistors. One tied to each neg. coil primary, then tie the two together and hook up the tach there. Wild guess value 100Kohms. The resistors need to be enough to trigger the tach but not the other coil

14vdc/200kohms=70microamps

"Just like Edison, I will attempt to proof something I know nothing about."

[audijunky]

I am thinking that you use both wires going to ground after the coils. No need for the resistors. Basically a signal gets sent alternating to bth coils. There is a ground or return line( might be just one for both) coming from the coils to ground. hooking up the input line for the tach so that it gets a signal from both coils should do the trick. I have hooked up an aftermarket tach to mine as well but I cant remember right now exactly how it was done. Hopefully someone else will chime in. Do a search for "aftermarket tach" thread started by me. There is some good info on it.
Good luck

[audijunky]

I found it
http://www.xs11.com/forum/showthread...threadid=11601

[ricoc]

Looks like you have a 2cyl tach, mine only goes down to 4 cyl. I didn't get a chance to try today. Hopefully tommorrow

[audijunky]

You are right mine was made for a Vtwin. That is why I only connected to one coil for the input signal for my tach. As you say that yours is for a 4 cylinder, I was thinking you should hook yours up to both. . I dont think a resistor would be the way to go anyway. I am thinking more like a diode. A diode blocks a signal from going one way but not the other. Any way From reading the other thread mentioned, It looks like there should be two wires returning from the coils going to the TCI or ground. IF you use both you should put diodes inline between the coils and the connection point where the two return lines connect before going to the tach. The wires you use to feed the tach should be T'ed off of the wires going to the TCI from the coils. I tried to draw something up to help and here it is. The small rectangles are the diodes, the middle sized rectangles are the coils, and the large rectangle is the TCI, the cirlce is your tach. I ommitted the power wires for your Tach and Coils, the drawing contains just the signal wiring. hope this helps

[ricoc]

Well.... I used a couple 100k res. instead of diodes, wired the same as your drawing. And it works! I figure the tach is a voltage sensing device so a high ohm would see minimal current. and that's also why I'm not getting extra sparks between the coils either.

Woohoo it works!

BTW diodes frighten me