Avanti II Tach

[jirvin]

I know parts of this have been covered in other threads but I have not found what I need. I have a 1972 Avanti II and my tach no longer works. There is a mish mash of wires under the dash and hood from previous owner. Got these claened up and I cannot get tach to work (it was not working before). Folks tell me I need the sending unit that goes between the ignition (coil or ignition box ( I am running Crane Hi 6 multiple spark discharge ignition with a wire clearly labeled Tach)). I have checked all the usual sources and found that the unit for 1972 is no longer available.

Any suggestions for sources or fixes?

Thank you all for keeping the spirit alive

[Gunslinger]

Your car originally came with a tach sender attached under the dash as you said. That Crane unit may not be compatible with it even if the tach worked normally. I can't say for sure on that but the technologies behind each are decades apart. The Crane may require a more modern tach to wire directly to.

I'm thinking you need to replace your tach with a modern one. When I purchased my '70 the tach didn't work either. I replaced all the gauges with Auto Meter replacements. They look great and are very likely far superior to the originals.

There is at least one vendor who sells replacement circuit boards for the original round can tach sender used by Studebaker, but I think yours has the squarish plastic sender. Check through some issues of Avanti Magazine and see if you can find the ad. I'm out of town right now so I can't look in back issues for the vendor. Maybe someone here will have the vendor's name.

[WayneC]

Gunslinger, I replaced the stock distributor/coil setup with a GM HEI distributor in my '71 Avanti years ago and found the tach worked fine getting its signal from the HEI's tach attach terminal;

required my finding the correct GM wire terminal to mate to the HEI tach (and I replaced the pink resistor wire to the distributor with a normal wire as part of the swap).

Can't say for certain, but my guess is that the Crane output signal is probably the equivalent (an intermittant 12v signal, same as a points distributor) and would probably work if he had a working sender.

One possible way to find out if the sender works might be to run a wire from the tach terminal of another running car (either points distributor or HEI) to his sender's input wire (with Avanti ignition on).

My guess is that his tach will register if the Avanti's sender and tach are both good.

There may be a way to use a multimeter to check the output of the sender, but you'd need a known good Avanti to find out what the reading should look like... my guess is that the sender

puts out a variable voltage signal.

Beyond that, he'd probably need to swap parts with another Avanti to find out which component is bad, or as you suggest, swap out the old speedo & sender for a modern electric tach setup.

[WayneC]

Any suggestions for sources or fixes?

Today I was looking through a stash of Microsoft Word documents I've saved over the years, some of which are Avanti-related, and I came across this (perhaps it'll be of some help)

I'm not sure whether I wrote it, or if I found it somewhere...

Thoughts on checking a bad tachometer on an Avanti:

Luckily I haven`t had to worry about this problem as yet, but here`s a couple of hints and thoughts: start by checking all the wiring to the tach sender and the tach itself for loose or corroded connections.

The tach sender is a flat cannister about 4 inches in diameter by a half inch high, located on top of the horizontal steel dash support, just below and to the right of the tach head.

There are 4 terminals on top of it.

The tach sender gets its rpm timing signal from the negative terminal on the coil to the terminal marked `D`.

The sender gets 12v from the circuit used for the automatic shifter... this is the 2-amp fuse in the fusebox closest to the circuit breakers... check the fuse and check for 12v to the sender terminal marked `+`.

There is a terminal marked with the grounding symbol which should have a white ground wire attached... check this wire for continuity to body ground.

Lastly, there is a yellow wire from the tach sender terminal marked `M` to the brass terminal on the back of the tach head.

On the tach head there also are 2 black power leads for night illumination bulbs, and 2 white leads for ground for those same bulbs.

I`m not an electrical techie so I do not know how to check for the signal from the coil to the tach sender `D` terminal and from the sender to the head (yellow wire) but I guess I`d play with the 12v setting on a fuse-protected ohmmeter to see if that picks up any kind of reading at the `D` and `M` terminals on the sender and the brass terminal at the tach head that varies with engine rpm.

Hope that all made some sense.

Edited November 20, 2015 by WayneC