How to wire factory tach with matchbox distributor?

[dgi]

Man, am I confused...

 

I'm trying to get a factory tach working on my 72 510 with a matchbox distributor. And, I'm having no luck at all!

 

I've even tried two different tacks... one I'm not to sure of, but the other one was working when removed from another car with a points dizzy.

 

Can someone give a pointer here!

 

TIA,

Terry

[datzenmike]

Whether points or EI dizzy the tach input signal wire is connected to the neg. side of the coil. Should work.

 

Some older? tachs are connected in line between the neg. side of the coil and the dizzy.

Edited November 4, 2009 by datzenmike

[tlap]

I was having issues also, I am using a Matchbox dist. too. Did you see this post?

http://forum.ratsun.net/showthread.php?t=11055

[MicroMachinery]

I'm running my 3-wire style factory tach to the negative side of the coil. Also running a matchbox dizzy. Works great.. you may have to adjust the variable resistor on the back of the tach. That was what was throwing me of for a long time.

[dgi]

I was having issues also, I am using a Matchbox dist. too. Did you see this post?

http://forum.ratsun.net/showthread.php?t=11055

 

Yep, but that isn't the factory tach for a 72. Might have started out that way, but I believe it has been "adapted" to use the later 3 wire tach. There is a post somewhere here and on DimeQuarterly about it (that started a ruckus).

 

Both of mine have a wire for the light, one for the ground, one for +12 switched, and two white wires that go in series with the coil.

[hang_510]

... and two white wires that go in series with the coil.

 

have you tried reversing the 2 white wires?

common prob = easily solved

[dgi]

have you tried reversing the 2 white wires?

common prob = easily solved

 

Yes, I have. Not the solution.

[dgi]

A bit more information for those willing to help.

 

Both of these are factory inductive tachs from 1972 510. One white needle, one orange needle.

 

Discussions elsewhere with folks who should have enough experience to know fall roughly divided.

 

• Three say that "the inductive tach won't work with the EI distributor".
  
• Two say "sure it works. I've done it." but can't remember how to hook it up.
  
• One said "I'm got one on my Z and it works." and sent me a diagram of the wiring. And that hookup didn't work either.

So, unless someone here can prove me wrong I'm gonna say that you can't get an inductive tach to work with the EI distributor.

 

I hope someone proves me wrong! :confused:

[hang_510]

well if 3 have it functioning, then 3 are still on your side... :confused:

 

 

why would it NOT work?

 

 

 

mine works perfect. is that 4? i can make it 5, since it also works on the other goon i put one in.

 

 

 

OR maybe you have a broken tach.

 

do you know if it was working before you got it?

[mklotz70]

There realy isn't any reason that I can think of that would keep a tach from working with EI. The only difference between EI and points is how the ground to the coil is turned on and off. With points, it's a mechanical switch....with EI, it's an electronic switch. They both simply cycle ground on and off for the coil.

 

The stock tach with the white wire gets wired in series with the coil. It seems counter productive to a good signal to the coil. You pull the wire off the neg term on the coil and hook it to one of the white wires. Then hook the other end of the white wire(same wire, simply coiled in the tach. If it doesn't work, switch them since polarity does matter. I had a matchbox dizzy on my wgn with a factory tach.

[dgi]

Sure, I could have a broken tach...

one I'm not to sure of, but the other one was working when removed from another car with a points dizzy.

 

Yeah, Mike, the inductive tach seems a bit counterproductive. However, I am trying to remain stock appearing and wanted to use what I had.

 

I agree with your description of the hookup and believe me I have tried it that way and swapped the polarity too.

[mklotz70]

Do you have a dedicated ground to the dizzy? Have you double checked that you have a good ground to the black wire and a good 12v to the green wire? The tach needs that power to operate...the white wire is simply the trigger. It's the equivelant of the ring in the center of the EI dizzy :)

 

I understand running the stock tach despite the inductive pickup. I ran one. I was a bit surprised it didn't affect the running at all. :)

[motavated]

My stock tach works fine with a matchbox on my 620. Is that what you guys are talking about? If it will work? 720's have tach's and dizzys. It should work...

[dgi]

Do you have a dedicated ground to the dizzy? Have you double checked that you have a good ground to the black wire...

 

Another one for Magic Mike! Dedicated ground... now why didn't I think of that?

 

I'm not gonna fret about why the ground I had originally used didn't work. I verified it using a VOM, but neither tach liked it.

 

A dedicated ground did the trick.

 

The known good tach came right to life, just needed a bit of adjustment.

 

The other one, a white needle tach, jumped a bit but didn't work. A little fiddling with the potentiometer and it came back to life also, ready for adjustment. Not too surprised... it has been on my shelf for many years.

 

Now both tachs are working fine and are calibrated correctly at 1000, 2000, and 2500 RPMs.

 

This exercise has gotten me intriqued on "inductive" tachometers, how they work, and how to accurately calibrate them. I think I will build/buy me some gear to more thoroughly verify their accuracy.

 

Thanks to everyone. And a special thank you to mklotz70 :)

Edited November 15, 2009 by dgi

[mklotz70]

Sweet! I got lucky again!!! :)

 

Glad to hear you got it working!!

 

Everyone always got a laugh over my factory tach in my automatic wgn.... :)

[moparvwfreak]

congrats. at least its working. i still need to wire in my tach and it seems like its an early tach. and i would like ot know how to adjust it if need be.

[hang_510]

The other one, a white needle tach, jumped a bit but didn't work. A little fiddling with the potentiometer and it came back to life also,

always start w/the free or easy things first! ;)