How to connect a tach to HEI distributor?
 

hi guys,

I just tried to install a tach to my HEI distributor.

No the Tach terminal is already connected to a white wire, running somewhere I can trace it to. I dont have a tach in my cluster, so shouldnt the tach connector be open?

Anybody know why the tach connector would already be connected in my car?

Re: How to connect a tach to HEI distributor?
 

Do you have a remote start system on the truck? If not, maybe a PO had an aftermarket tach installed and just cut the wire and left it in the dash somewhere.

Re: How to connect a tach to HEI distributor?
 

nope, no remote start. ans the wire is part of a connector that looks original and is for both connections.

I'll try to trace the wire. But it is all taped up!

anybody?

Re: How to connect a tach to HEI distributor?
 

I would disconnect the existing wire and hook up the tach. See if the truck will start and drive it around the block. I'm not familiar with the white wire you're speaking of. Another option would be to connect the existing wire and your new tach wire together.

Re: How to connect a tach to HEI distributor?
 

I agree. I don't see the white wire being very important especially coming from the tach output.
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Re: How to connect a tach to HEI distributor?
 

OK! thanks for the advise.
I checked the Chilton manual today and it shows the white wire in the electrical diagram from my 86 mode. going from the distributor to the tach.

could it be that they already ran a wire, but didnt connect a tach?

so this tach connector has no other function than to connect to a tach?

Re: How to connect a tach to HEI distributor?
 

Hi kikkegek,

What type of carburetor is on your truck?

The reason I ask is because GM used some carbs with a computer-controlled mixture solenoid setup in the 80's. Mostly found on cars but I've heard some trucks got them too (California emissions mostly I think).

Anyway, many of those computer-controlled carburetor setups have a wire connected to the HEI tach terminal to send a tach reference signal to the computer. If that's the case, you'll need to keep that wire hooked up, but I don't see any problem tapping into it to hook up your new tach.

Re: How to connect a tach to HEI distributor?
 

hi there. I checked and the white wire is not connected to the carb. But I cant seem to find where it goes...I only see it drop down behind the engine to the passenger side and dissapear into a hose (cover) for several cables. Cant seem to trace it where it goes to.

I'll just tap into it and see if my tach works...I'll be back!

and YES, my engine had lots of california eco-stuff on it we all took of. since there is no need for it in Europe. The car was imported from california last summer

Re: How to connect a tach to HEI distributor?
 

tested it just now. connected 12V and ground to the battery and the S (rpm signal) to the TACH signal from the HEI. But I get no rpms displayed.

help?

Re: How to connect a tach to HEI distributor?
 

does anybody have the wiring diagram for the ECO part of the engine? My wiring diagrams from Haynes and Chilton only say the white wire from the TACH connection should run to the tachometer. But doesnt in my case.

There is a vacuum diagram in teh Chilton, but no electronics. please help.

Re: How to connect a tach to HEI distributor?
 

How many wires do you have with your tachometer? I believe there is supposed to be a green, red, black, and white...The white should be for the lights...and should be spliced or connected to the lights to where when you turn the headlights on...so does it.....the black should be the ground.....red should be connected to the ignition switch because you want it to turn on when you turn the key on.....and green should be on the negative post on your coil.....which should be on top of your distributor unless you have an external coil...don't take this 100% but I think that's how everything is hooked up

Re: How to connect a tach to HEI distributor?
 

Hi kikkegek,

I don't have a diagram for the Calif emissions feedback carb wiring, but I'm pretty sure that white wire off the distributor runs to a control module mounted under the dash (behind the glovebox).

Since you removed all the emissions stuff, I think you can safely unplug that white wire from your HEI and replace it with the wire going to your tach. Try that instead of tapping into that wire as I had mentioned earlier. Although unlikely, there might be something in the control module at the other end of that wire that's keeping the tach from getting a good signal.

Re: How to connect a tach to HEI distributor?
 

Looking in the Haynes 1967-85 workshop manual. They show the white wire going to:

81-85 years
6 cyl - A.I.R diverter module
8 cyl - speed switch relay

The 77 up years don't have a white wire but instead a brown and that wire is shown to go to the tach clusters

I would disconnect the existing white wire and connect your tach lead there!
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Re: How to connect a tach to HEI distributor?
 

he thanks man!

what is the speed switch relay for? what does it control? or check?

Re: How to connect a tach to HEI distributor?
 

kikkegek found it page 12-12 @ the back
i'll post it in a bit...looking for cam

Re: How to connect a tach to HEI distributor?
 

posted

Re: How to connect a tach to HEI distributor?
 

thanks man!
i did it. tapped into the white wire and the tach is working.

as soon as I got it built into the dash I'll post esome pics.

its a relly nice little tach that will fit realy nice!

Re: How to connect a tach to HEI distributor?
 

I just finished adding a tach in where my clock was. I think it came our really good!

http://i69.photobucket.com/albums/i4...y/d52577f9.png

http://i69.photobucket.com/albums/i4...y/b7f9d192.png
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Re: How to connect a tach to HEI distributor?
 

he man! i am gonna do exactly the same. my tach is a small one like yours too! looks good man!

only mine is yellow lit, and I cant seem to be able to open the thing!

Re: How to connect a tach to HEI distributor?
 

That's strange. So there is no socket on the back for a bulb?

Who is the manufacturer of the gauge?
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Re: How to connect a tach to HEI distributor?
 

weird that means you can't replace the bulb?
i had to pry my case away from the edge to take my autometer apart(to fix short)
but the bulb i could get from outside
and i used a trailer hitch plug for ez in out

Re: How to connect a tach to HEI distributor?
 

how did you mount your tach inside your dash? any pics?

Re: How to connect a tach to HEI distributor?
 

I just replied to your question over in my build thread
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