Wiring in a tach; not the typical how to ?

[Bummer72]

Hello again,

I purchased and am attempting to wire in a Sunpro II tachometer. I understand that this tach should be wired red wire to switched power, black wire to ground, white wire to instrument lighting, and green wire to the negative post on the coil.

My problem is that it appears I'm not getting any signal to the tach.

I asked myself, did I fry the tach by accidentially crossing a wire? No, I am very confident I didn't...so confident, in fact that I exchanged it for a new one, thinking the tach was defective. Got the new tach and wired it up again...same thing! The tach powers up, the needle floats up to "0", the backlight comes on, but the needle doesn't move above zero.

Well, since its unlikely a second unit would be defective, I pulled out my multi meter w/ RPM function to do some troubleshooting.

First, I disconnected and checked at the junction where I spliced on more green wire to extend it forward to the coil, to see if perhaps my extention wire was broken somewhere along it's lenght. Again, no reading on my multi-meter. I think, ah-ha, now I'm getting somewhere...the wire must be bad.

So I take the other end off the coil, set my multi-meter to the ohm setting, and check the wire end to end. Absolutely no resistance...the wire is good.

Okay, so I go back to RPM function on the multi meter, start the engine, and check the coil (-) terminal for tach signal, and I get Almost Nothing....by that I mean, I'll get a reading, but then the reading drops down to zero withing a moment, almost like I'm trying to use a flashlight with dead batteries, and the light comes on for a moment, but then fades out to nothing! WT#$@$%$#

Some internet wild a$$ guessing I did was searching "no tach reading from coil" Google returned meTHIS.
That led me wonder if the coil might be backwards, and if it would run like that. Google search for "ignition coil backwards" gave me several hits that say it would. I don't know if that would affect the tach or not.

So again, I don't seem to be able to get a usable tach signal from the negative ignition coil....Anyone have any ideas why???

Thanks,
Doug

[fireguywtc]

I would do two things:

first check to make sure your tach is selected for the proper engine size, 6cyl, 8cyl, etc.

next I would run a wire all the way to the coil post itself rather then splicing. That is how I wired mine by putting a small round end on it to go over the post. Maybe you are not getting enough power from the splice like you mentioned.

[Bummer72]

PROBLEM SOLVED!

So, after my post, I did some more research. I had a hunch that my coil was the issue...it was, sort of. Remember, the green tachometer wire goes on the (-) post of the coil, right......

Well...when I read that the (+) terminal on the coil should be the wire coming from the ignition switch, and the (-) terminal should be going to the distributor I thought to myself, just what if the coil is arse backwards??? If that were the case, I would have been hooking my tach up to the wrong side!!!!!

And that was in fact exactly what was wrong...the coil was installed reversed were hooked up backwards, leading me to believe that the (-) terminal was the terminal post holding the wire that leads to the ignition switch, and causing me to hook the tachometer wire up to that side of the coil, all of which, of course, is incorrect.

So, in summary: The tachometer wire needs to be on the side of the ignition coil that leads to the distributor. The coil should be installed so that the (+) side contains a wire coming through the firewall from the ignition switch. The (-) side of the coil should lead to the distributor.

And now I know!

[67mann]

We must have the same people installing our coil.....because I just went through all that Sunpro II tach.....nothing on Neg side or what I thought was the Neg. side.Switched it to the + side and everythings good