tach wiring

[blazen88]

i have an old tach do any one no how to wire this up {hei dist} it has four wires
green wire labled positive on tach
white wire labled negative on tach
red wire runs to a light bulb
grey wire runing to same bulb

 

[cybrfire]

Green wire goes to the tach pole on the distributor and the white goes to the ground pole on the distributor.

Grey wire usually to any chassis ground
Red wire to something that goes hot with the dash lights, ie. another gauge light, brown accessory terminal in the fuse panel etc.

 

[Fabrimacator21]

Did the tach work? Are you pulling this off a truck and putting it on yours? Is this a stock or after market tach?

Just going from how mine hooked up, usually red is positive. There should only be one wire going to the light... mine was white, sounds like yours is grey.

You have four wires and they should/usually go as follows...

1. positive
2. ground
3. signal
4. light

Sounds like the signal/green wire isn't hooked up to the dizzy.

Red SHOULD be pausitive. What do you mean by "labeled on the tach". Is it something someone wrote on it or is it actually manufactured like that?


If your gonna start swapping wires around to see what works I suggest you wire a fuse (10 amp) into the hot wire so you don't blow it up if you don't hook it up right. They are only a buck or so at autozone.

To put it simply I think you need to hook up the red to any 12v source, The white to any chassis ground, The green to the signal on the dizzy and the grey to the light.



Cybr: shouldn't there be only one wire going to ground? The way you told him to hook it up theres no wire to power the light(although I guess you could splice another wire off the hot to power the light).

 

[blazen88]

i got this out of and old rv proublay in the early 70s on the housing of the tach it has a + sign and - sign and the green and white wire attached to the post

 

[Fabrimacator21]

I'm assuming by "post" you mean battery...

if that's the case, it looks like the grey wire is you signal then..... Should go to the dizz.

The red should be lights.

An easy way to find out would be to hook up green to pausitive, white to negative and red to light(leave the signal/dizz wire off). If the light comes on then you know your right and you can hook up the signal to the dizz... if the light doesn't come on (make sure the bulb is good) then swap them, but grey should be signal. The signal wire usually alternates between grey or green depending on how old the tach is.

I still say get a fuse wired into the hot wire before you try anything though.

 

[cybrfire]

The description of where his wire are coming from/labeled is kinda bizarre.

Two wires to a light bulb. One has to be pos the other neg for the light bulb.... Usually one is to an ignition hot.... he has two to the light bulb so not sure. One of these could be to an ignition source.

One is a green wire which in my experience is always to the tach terminal on the distributor. The other is white which is labeled negative. There is a neg. terminal on the dizzy if memory serves. Any chassis ground can work probably.

What brand is this thing??

 

[Fabrimacator21]

The description of where his wire are coming from/labeled is kinda bizarre.

Two wires to a light bulb. One has to be pos the other neg for the light bulb.... Usually one is to an ignition hot.... he has two to the light bulb so not sure. One of these could be to an ignition source.

One is a green wire which in my experience is always to the tach terminal on the distributor. The other is white which is labeled negative. There is a neg. terminal on the dizzy if memory serves. Any chassis ground can work probably.

What brand is this thing??

I agree it is bizarre but two wires into a light is a red flag for me.... that should be wired into the ground wire internally through the tach.... in other words there should be one light wire coming out of the tach, not two. I've never heard of two wires to a light. Me thinks the grey wire running to the bulb is the signal wire(someone hooked it up wrong). I'm pretty sure the OLD tacs used grey for signal... the wire coming off the coil (for signal) on my 1978 305 boat is grey. Since he says the tach is labled green hot, white negative, the other two can only be signal and light. I'd assume that the grey wire would be signal since thats how my 1978 boat is wired.(that leaves red as the light wire)


Blazen88: autozone has tacs for 35 bucks and they are pretty decent.... sounds like someone fubared that tach. I'd try green hot, white ground, red light, and grey signal.... if that doesn't work I'm guessing it's blown.

 

[4X4HIGH]

i got this out of and old rv proublay in the early 70s on the housing of the tach it has a + sign and - sign and the green and white wire attached to the post

Red is keyed 12 volts, green is tach signal (hook to HEI post marked TACH), white is for the light, and whatever color your last wire is is chassis ground (usually black wire).

 

[blazen88]

well check this out if you didnt have any wires on the back of and old tack you have two post to connect a wire use a small nut one says negative and the other positive what would you do this is an old DELTA tack with a dial in the front to ajust the rpms i asume the bulb only comes on when it reaches the rmps you set it at ill worry about the light later this is an old tach that looks pretty cool and i be damn it says it was MADE IN THE USA so do i run the posi side to the distrubuter and just ground the neg will it work that way