tach wiring - please verify my diagram

Is this accurate?

Just installed an Autometer this weekend. Blk-ground,Grn-neg. coil,Red-hot and White to headlight or dash light fuse.

Sorry, I should give more detail:

I'm retro-fitting a factory tach into a non-tach car, so none of the wiring is there.

It's a '66 factory tach w/ a separate sender like this:



I'm not sure whether M goes to the + or - terminal on the tach - the FSM wiring diagram doesn't indicate this for some reason. I'm assuming it sends the signal to + because that seems intuitively correct, but you know how that goes.

The other thing I'm not totally sure about is which terminal on the tach is + and which is - since one is gold and the other is silver. Is gold usually the +?

Also also, will this work with an ignition system upgraded to electronic? e.g. is the signal at the - side of the coil the same as it would be with a points setup?

Excellent questions! I am doing the same for my 1966 Satellite. I have the tach and sending unit but I am not that far along to hooking it up yet. So this will be very valuable info for me!
Your tach sending unit looks in great shape. I am not sure mine will work. I am not so concerned with originality but more importantly is the functionality. Are there any sources for an external sending unit that will work if mine is no good?
Also, do you have to run all these new wires or can you splice into the factory wiring harness?
Did they really use 2 different wiring harnesses for tach or no tach? I know certain options were pre wired from the factory if you got it or not.
I have electronic ignition as well.
Hope someone (maybe with an original tach car) can help.

The tach will work with stock-type electronic ignition. It may or may not work correctly with an MSD or other multi-spark system. The "M" goes to the plus on the tach. The other side goes to ground. Since the tach is a simple meter, it stands to reason that installed backwards will cause it to move the wrong direction. I would use an ohmmeter to check it. The meter movement (the needle is attached to it) will move slightly when the meter is applied. It should move in the positive direction when the red (+) lead is on the positive side of the tach and the black (-) lead is on the ground side.

It's been nearly 20 years since I owned a 66 Barracuda with a factory tach.

It looks to me like you have it hooked up correctly.

I make aftermarket 66 charger tach boards. I will upload the manual I wrote for my tach board as it has some information about how to connect things. You will have to ignore the parts about adjustments as those are specific to my aftermarket tach board.

By the way, I sell my board for $75 plus $10 shipping if anyone needs one. I am in the process of coming out with 67-74 tach boards as well. My board fits inside the original sending unit can, so the originality of your car is maintained. I use modern electronics so you don't have to worry about the board going bad on you like the original boards.

As far as the wiring harness, you should be able to splice into the hot wire. But you will have to run the wire that goes from the coil to the sending unit, and the wire that goes from the sending unit to the tach.

Sometimes you can fix the old sending units, usually the capacitors are dried out. I have also seen a few with fried transistors. I have seen some with fried transformers, and these would be very difficult to fix.

P.S. I tried to attach the PDF file, but moparts only allows attaching pictures. Here is a web link to my tach board manual:

http://www.rt-eng.com/mopar/TachBoardManual.pdf

Greg Garner

If I remember correctly, the tach on the 66 charger only has one terminal on the back, and that is the + side of the meter. The minus side of the meter is the case of the meter, which should be hooked to ground. If your tach has two wires, it could either have a + and - for the meter, or it could have + for the meter, and another wire for the light inside the tach, with the case of the meter being ground. You can usually take these tachs apart without damaging them if you are careful, and you can look and see if the two wires go to the meter movement or if one goes to a light. The suggestion with the meter was a good one in order to find out which wire is positive if both + and - terminals of the meter are available. I sometimes pop a tach with +12V for just a very short period of time to see which way the meter moves. Do not connect 12V to the meter for more than about 1 second or you could fry the meter.

Later model tachs (67-74) usually have two wires going into them (D for - side of distributor, and +12). The case is ground on the later model tachs.

Great! I was worried that everyone would say try to find a good used or NOS. I thought the last time I looked, the black tape was falling off and it looked pretty corroded. Maybe it will work and maybe it wont. If not, at least I know Greg makes aftermarket ones.

Where is the best place to run the wire through the firewall to the coil? How did the factory run the wire?

The factory ran the wire through the firewall connector as part of the engine wiring harness. My car never had a tach so no connectors.

I've run various extra wires through the rubber firewall grommet that the vacuum gauge hose and temp sensor wire run through, so that's what I'll do for this wire (only one wire needs to enter the engine compartment, the one that goes to the coil). It's a little round grommet near the center of the firewall. It had holes for two tubes/wires in it - I just cut the middle out of it to fit more wires through and it looks factory. Might be a different setup on your car.

I'm also psyched that Greg makes a replacement board - I have no idea if my sender still works.