Tachometer signal connection

[engineer bill]

My coach is a 1989 Chevy L7.4 454 P30, carburated. From studying the service manual I see that the distributor and coil are all in one unit. The manual has a diagram that refers to a "Tach Connection" but it is not clear to me exactly how access the terminals and to find the right one. Anyone have any experience in connecting a standard tachometer "Tach" lead to this distributor?

[Rickf1985]

Hi Bill, If you look at the terminals on the distributor cap where the power wire comes in, they come up from the bottom towards the top of the cap and off on the side. You will see one of the terminals is marked "tach".

[cncsparky]

If the tach connection is unused on the distributor, you will need a female 1/4" spade connector for it.  Mine was being used for the cruise control(I think), so I just tapped into that line.  I believe it was a green wire.

[engineer bill]

Thanks! After looking closely at the connector on the side of the distributor cap, I disconnected it and took a look at the wires and the marking. Aha, all was clear to me. I tapped into the "tach" wire using one of these (see attached) to make a nice clean connection with no wire damage. I wanted to presearve the integrity of the existing tach wire (cruise control?) I still hope to get the cruise control running someday - and no, I won't be using it in hilly country, only on miles and miles of flat I5 here in California.

Thanks everyone.

[Rickf1985]

What kind of tach do you have and did this work?

[engineer bill]

Well. I tapped the tach signal as described above. I used an 18 ga stranded copper automotive wire and started routing it to the cab. At about that point I noticed that the PO (s) had drilled a bunch of holes in various places including above the wheel well. Wires coming and going everywhere and not a grommet in sight. So, I started looking for a good place for one big grommet. Obviously, you need to be able to line a drill up to make the hole. Or maybe a punch, I suppose. I thought about pulling the putty away from the factory harness pass thru but decided against disturbing it. After a while, I think I found a good place. Out of the path of direct water flow while driving. It's hard to describe so I'll take a picture soon. Electrical harness putty is on the way from Amazon. I want to integrate the tach wiring with the other gage and switch wiring in the cab so fuses and terminal strips are in my future. I'll document it here.


The Tach is an Autogage 2300 series. Not very high end but I think it'll do for now.

[Rickf1985]

Bill, look under the hood about 1:00, you might see a group of wires coming down from above. If it is there you can sneak the wire up through the center of that bundle which on the other side is under the dash in front of the dogbox about even with the left side of the dogbox. I have to take the dogbox off on mine because of a cupholder/console on it, but with it off you can see and reach both above and below for the wire.

[Oz]

Why do you have to look under the hood at 1:00?  Why not 2:30. 5:00 or even 3:am?  Is it only visible at 1:00?

[Rickf1985]

Smart azz! No, it HAS to be one O clock!

[joanfenn]

Is that AM or PM?

[TerryH]

In which time zone? Hm? :)rotflmao

Metric or Imperial?

[Oz]

See what you started, Rick...

[M & J]

If it was military time youd know AM or PM.

[Rickf1985]

Tough crowd! Bills an engineer, he will figure it out.

[Rickf1985]

In which time zone? Hm? :)rotflmao

Metric or Imperial?

Metric or Imperial time??   Yes I was paying attention.

[engineer bill]

For those following the Tach connection thread from home, you will remember that we had just found the attachment point for the "Tach Signal". Please note this warning that I found in the Service Manual:


"Notice: The tachometer terminal must Never be allowed to touch ground, as damage to the module and/or ignition coil can result."

[HandyDan]

Maybe this will help.