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Discussion Starter #1
Got a 76 SS and it has the vacuum (economy) gauge. Want to install the factory tach in it's place. The Tach has 7 studs on the back but only 3 receptacles for studs to insert into the instrument cluster case. Cannot find any source to identify the 3 contact points. Also cannot find the pinout identity of the printed circuit board. Ant help would be greatly appreciated.
 

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Hi Cruisers, welcome from Idaho. Glad you've joined us. I've made that change to my 5th Gen, I think the 4th Gen are probably different. Others should be able to help you with that.
 

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Discussion Starter #5
welcome C
is it a square sweep or round speedo dash??
gauges or idiot lights ??

power - pink from gauge fuse
ground - black
tach sig - white,, maybe if its there ??
Wiring Diagrams 59-60, 64-88
The gauges are round and it is the gauge cluster NOT idiot lights. You mention Pink, Black and White wire. Are you speaking of the harness that plugs into the PCB? In the diagram I don't see anything labeled as "Tach" anywhere. In the PCB connector I do see Pink and Black wires, but NO White. If you are looking at the rear of the Tach, which of the 3 stud plug in points is which?
 

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yes the harness that goes to the PCB..
the PCB may be different for without a tack dash, so the white wire wont be there..
youll have to add the white wire from the distributor or coil negative terminal..
yea, that diagram is just a generic idiot light wiring.. but the pink and black should be right..

are there any markings on the tach ? like 12v, power, GND, signal, + or - ??
if not
hopefully someone with a 76 manual and wiring diagram will chime in..
the book will have a pic of the round/gauge/tach PCB to trace the tach inputs..
 

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Discussion Starter #8
First, thanks to all for the help. There are no indications as to what each of the 3 stud connectors are. I don't want to guess at which is which as this Tach is NIB and very expensive. Therefore I cannot afford to fry it with a wrong/reversed connection. I have the Kent Moore Tach driver tester, BUT I have to know for sure which is which.
 

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I understand, I like to have a picture..

if you can find a good PCB pic and trace it out, the pos+ and neg- will be obvious..
there may be 3-4 PCBs for the different dash's..
sometimes there is a fuel gauge in that hole, I think ??

like this, but its too small to see.. not sure if its a tach or fuel..
Chevelle Printed Circuit, For Cars With Gauges, 1975-1977
 

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Discussion Starter #10
Want to see if anyone can help. The person in this thread posting as "Donny" works with American Autowire. I was told I could not speak with him when I called there. He appears to know more about this Tach situation than anyone else I've found on the Inet. Does anyone know how to reach him? I would just like to run a few things by him in regard to the Tach install on a later model than it came on. I would like to bench test a NIB Tach but don't want to fry it with incorrect hookup.
 

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Cruisers, I just got a used factory tach for my 5th gen. after reading your thread here, I started examining mine closely. while the layout on mine is different (2 posts on 1 side, 1 on the other), I did notice that my actual circuit board was labeled with Coil, 12v and GND, where the clamps are soldered on for the screws to push into. you may want to take a closer look and see if you see something like that, even if it requires some disassembly
 

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Her are pics of the tach I am installing. I marked the + (top left), Ground (a bit ambig but top right), and Signal posts (wire feeds through the hole in the back of the cluster). Also pics of the front and rear of the cluster. If you are using a stock cluster you don't really need to know the identities of the posts because the flex circuit board does the work. You can also trace the path of each path on the circuit and see what pin it corresponds to, then compare that to the wiring diagram to identify the wires. I had to do that when I repinned my cluster connection.
131031


131032


131033


131034
 

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Discussion Starter #13
Compared mine to yours. Mine has 7 studs and yours has 5. The circuit board looks very different than yours. The PCB looks the same, the cluster housing looks the same. I know I can trace out the PCB to find the + and- BUT, the bulbs don't care which is + or- they'll work. BUT the electronic circuitry of the Tach board very well may be polarity sensitive. Thus ruining the Tach with a reversed hookup. I've never hooked up to an electronic Tach that this Kent Moore tester would not drivet. But it will not do anything to either (have 2) of these Tach's.
 

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It's kind of hard to see in the pic but mine has 6 studs--but your point remains. They are not the same. If yours is NIB, then mine may very well have been refurbished at some point. I hope you can get it figured out! When you do, post up pics and everything so we will have a good record. In fact, if you post up a pic of the back of yours we might have more luck zeroing in on the right info. I had to do a lot of digging to identify mine and figure out a test, so I may have run across yours at some point.
 
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