Tachometer enquiry

[johndowney]

First time poster...please be patient!
Some years ago I picked up a set of old gauges at a boat swap meet. Mostly Stewart Warner except the tach which is AC. I would like to install this tach when I get around to rebuilding the control panel on my 1964 Cheoy Lee Bermuda 30. I have researched wiring requirements on this forum and it looks straightforward enough. Problem is that the terminals on the tach are not marked. There is one insulated terminal right in the center with a white/black wire coming out, two other terminals towards the bottom (these may be part of the casing as they don't appear to be insulated) and then two other studs for mounting at the 3 & 9 o'clock positions.
Does anyone have the same tach? If so can you help me identify the wires please?
Other markings on the rear of the unit are : AC 8c , 12v., 27934, 6411529
I will try and add photos to this post.
Thanks for your help.
BTW...I have sweet-running 64 old style to which I have added electronic ignition and a late-model starter. One of these years I will bite the bullet and attempt a major rebuild. Compression is kinda low in the low 70s all along the cylinders but she runs well.

[ILikeRust]

Hey, is that a purple terry cloth towel?

[ndutton]

Don't let the towel comment throw you, these folks have issues . . . .

I believe it can be safely assumed this tach gets its signal from the coil (-) terminal due to it's apparent age. The single insulated terminal is puzzling, I would expect at least two: one for 12V positive and the other for the coil (-). There could have been a third insulated terminal for the illumination light (+).

That's what I would expect. Of course, none of that is present, the reason for the question in the first place. How committed are you to this gauge?

[thatch]

John, First, welcome aboard. That tach looks very similar to an old AC unit that I "pirated" from a Buick and used on a V8 powered skiboat. Unlike other universal tachs that can be adjusted for engines with varying numbers of cylinders, this one is V8 specific. If it is still operational, it will most likely work on your A4, except for the fact that it will only read 1/2 the actual RPM's. As Neil pointed out, the white lead would connect to the -coil post. A ground lead would also need to be connected to the case.
Tom

[johndowney]

Thanks for the replies. A short story...When I first got this boat about seventeen years ago it had a non-functioning tach as part of a neat little grey "UNIVERSAL" instrument panel. A friend of a friend who happened to be a mechanic offered to replace the tach. What he actually did was to butcher my really cool instrument panel and shoehorn in a big old automobile tach from one of his old hot rods. It works but is really out of place and I have been thinking for a year or two of replacing the whole panel. This old AC tach will be great if it works. I kind of like old things...old boat, old engine, old terry towels!
So I think I will give it a shot with a temporary lead to the -coil and just try grounding the case. If it works I will pursue using it in the new panel. If you think this might blow up something please pipe up! Thanks...John
I will include shot of the front this time. Will try and figure out how to reduce size of image before posting any more!

[roadnsky]

Originally Posted by johndowney

...When I first got this boat about seventeen years ago it had a non-functioning tach as part of a neat little grey "UNIVERSAL" instrument panel...

There is a really nice blank instrument panel sold on this very site.
Just sayin'...

[Kelly]

John-

Please take a look at the visitor board on your personal profile page; I've written you a message concerning your B30 and Santa Barbara.

Thanks,
Kelly

[67c&ccorv]

I think you have a Sun Tachometer there...won't work on the A4 unless you send it for modification to a specialist who can modify it.

I put a similar Sun tach in my home made dash - I have the name of the company that does the mod if you are interested.

[johndowney]

Thanks for naming my "Sun" tach. I was thinking it was A.C. as in Alliss-Chalmers (sp?), now I realize that AC stamped on it refers to a type.
I just tried hooking up the only insulated terminal to the neg coil and then used one of the un-insulated terminals to ground. (tried the other one too) No dice! Yes please I would appreciate the contact of the people who converted your tach for A4 use.

Thanks also to the poster who suggested the blank instrument panel from MM. I think that's the best way to go when I get around to the rebuild of my panel.

[67c&ccorv]

Here is the company who modified my Sun Tach:

http://williamsons.com/