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so i have a set of gauges for my 1969 GTO, i bought the car with the dash removed and dissembled... trying to understand how the tachometer is wired. There is one post on the back of the tachometer that i assume is for power? ground is right to the body of the tachometer? and where does it receive signal?
 

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Zg
the tab on the rear is the fused PULSE wire from your coil .... - side
IF
your changing to oil water gas gauges in the left pod from a single fuel gauge
there is also sending units on the engine to swap out'
and
wires on the master plug at the circuit board and ignition switch also at least in 68 for sure
you will also need a Y light harness if you didnt have a clock originally for the illumination bulbs,,gray wire

you might consider spending 100 on some manuals ,,,,,

we like to help when we can .........

Scott

hey 1970 lets start a new chat about your dash pad ....
so this thread wont get hijacked from Zg




133075
 

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Discussion Starter #4
great thank you blk69judge.

so from what i have read, these pontiac tachometers are "single wire" units, theses tachs do not use a secondary power source as most gm tachs do. ia this correct?

which brings me to my next question, can i bench test this tachometer with a battery charger as i would other tachometers, AND what could i use as a single generator to complete a more comprehensive bench test?
 

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NO
your not testing a light bulb ...
if your tach is an original it should be checked by a qualified speedometer shop

often original tachs are way off calibration .... and need rebuilt....
I have an NOS GM hood tach that works perfect at idle but at 5000 rpm it reads 3300
the originals are just not reliable,,, unless checked first on another vehicle with a known calibrated tach
and running them side by side ... still kinda ruff on engines testing tachs at 5000

buy a new repop ... from AMES ... and the harness ,,,, You do not want to pull the dash back out very many times
and a lazy tach can cost you 1000's in engine repair over a 200.00 tach

just my opinion

Scott
 

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NO
your not testing a light bulb ...
if your tach is an original it should be checked by a qualified speedometer shop

often original tachs are way off calibration .... and need rebuilt....
I have an NOS GM hood tach that works perfect at idle but at 5000 rpm it reads 3300
the originals are just not reliable,,, unless checked first on another vehicle with a known calibrated tach
and running them side by side ... still kinda ruff on engines testing tachs at 5000

buy a new repop ... from AMES ... and the harness ,,,, You do not want to pull the dash back out very many times
and a lazy tach can cost you 1000's in engine repair over a 200.00 tach

just my opinion

Scott
also
if your running anything but a points distributor ,,,, you will want the aftermarket tach for its internal updates ..
 

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so i have a set of gauges for my 1969 GTO, i bought the car with the dash removed and dissembled... trying to understand how the tachometer is wired. There is one post on the back of the tachometer that i assume is for power? ground is right to the body of the tachometer? and where does it receive signal?
as other posters have said, the single terminal on backside of tach is for the (brown) fused signal wire coming from the negative side of the coil. The mounting tabs on the tach case serve as the ground. Separately , if your car had a tach in it already, there should be a light harness with the 2 bulbs (gray) or, if your car had a clock, you may be able to use the same light harness, or at least buy a harness from one of the suppliers and it will plug right into the gray wired 12v connector for your clock wire. Ive installed two of these in the last few years, one was original, one I bought from PartsPlace I think. I also bought the light harness from the, Here's a wiring diagram of sorts out of the Zazarine GTO book. Note, if your car did not have a tach, you may not have the Brown wire included in your original harness, in that case I just ran a fused wire from the coil thru one of the holes in the firewall and attached it to the tach. IMG_6262.jpg IMG_6261.jpg back of dash tach_reference.jpg
 
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