Factory Tach 1985 442, which post is ground, hot, coil?

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Hurst/Olds 73-74

Not-quite-so-new-guy
Jun 4, 2014
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I don't want to come across as a complete idiot, but there are some areas of a car that I'm just not knowlegable yet. I can't get the factory tach in my 1985 442 working, so I'm thinking about wiring it directly and bypassing the press circuit board on the back of the instrument cluster. The car has it's original engine, but has an Accel HEI Super Coil (140005) on top of the distributor. The tach has 3 prongs on the back of it.
1. Which prong is for the ground, which is for the power, and which if for the coil?
2. Which wire on the Accel HEI Super Coil do I splice into for the tach wire?
3. (Dumb question) On the back of the Tach, there's a red plastic plug that can go into the "6" or "8" box. This application is for a 307 V8, so do you put red plug into the "8" hole to indicate 8 cylinder use, or do you put the plug into the "6" and leave the "8" hole open for V8 applications?
 

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Hurst/Olds 73-74

Not-quite-so-new-guy
Jun 4, 2014
11
0
0
OK, I got the answer to question #2 from a friend. There's a male plug hanging down under the Accel HEI Super Coil just for the tach wire hookup. Just need to know about the 3 prongs on the back of the tach and the red tab now.
 

88hurstolds

Royal Smart Person
Jun 24, 2008
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The 8 indicates 8 cylinder.
The tach is one wire and it's white.
You can simply follow the path of the circuit board to the corresponding connector on the harness and then just run a straight wire with an eyelet to the speed nut on the back of the circuit board that correlates to the white wire if this makes sense...
Here is a photo of what I am referring to:


Here is more information:

http://tech.oldsgmail.com/eint_rallye_swap.html
 

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Hurst/Olds 73-74

Not-quite-so-new-guy
Jun 4, 2014
11
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0
Update: I got the tach and ALL of the gauges working!!! The white tach wire had been cut and was hiding down in a wire loom that held the pink wire that was still plugged into the HEI distributor. The gas gauge pink wire had been chewed in half by a rodent about 2 inches from the wiring connector behind the gauge cluster. It's nice to see all of the gauges working again!
 

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