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Discussion Starter #1
I am restoring a 68 rag with a roller tach. There have been new dash, engine, and forward lamp harnesses installed. Currently I am unable to get the roller tach to work. I have lights on the dash (so I assume I have a ground) and all the other gauges are working. However, I am using an Accel HEI super coil (the harnesses were built to accomodate this feature). Is this my problem? Will the tach work off this coil? I haven't checked yet but is one of the terminals on the tach suppose to have an insulator to prevent the sending wire from grounding out? To the best of my knowledge the tach is functional, but is there any way of checking it while it is in the dash.
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The tach has two connections on the back. The top should be brown that connects to the TACH connection on the HEI dist/coil cap. The bottom should be pink and have power when the ignition is on. The tach grounds by it's metal back. You can check for a complete circuit from the tach connection to the dist, the brown wire. You can use an ohm meter, disconnect the tach connection at the dist and at the tach and either ground one end and check the other end to ground with the meter or stretch the meter leads to each end and check with the meter. Check for power on the pink wire and if the tach back light works the ground is good.

The tach should work with the Accel coil. I have the same coil on my El Camino, the factory tach works fine.

Yes the tach should have an insulator on the signal/coil connection. If the "sending wire" (brown)were to be grounded at the tach, the engine would not run.
 

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Discussion Starter #3
The light on the back of the tach works, I will check for the insulator tonight, which fuse does the red wire get power from? Thanks for the info.
 

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I had a quick look last night,and there is an insulator type of a plate on the back of the tach which appears to be keeping both terminals from contacting the back of the tach. The brown wire is connected to the top terminal while the red is connected to the bottom. I have both a multimeter and a small pen like test light. I guess the first thing is to check to see if the tach is getting power via the test light, the signal from the distributor I will have to check with the multimeter. (what setting do I put the multimeter to when checking for signal with the engine running?) Also should there be some sort of rubber insulator between the screw which holds the terminal down and the top of that plate which I was describing? Thanks in advance, pston.
 

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I have never connected a volt meter to the - side of the coil. Not sure what voltage you will have when the engine is running, there is potential for high voltage spikes at four times the engine RPM. Someone else may have advise on this. I recommend you check for a complete circuit using the ohm function as described. Or I guess you can connect a volt meter to the brown wire at the tach, bumping the starter should give a reading of around 12 V. if the pulse circuit is good.
 

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old post here but did you ever get the tach to work ? mine works great with jumpers out of the dash. I put it back in the dash and nothing - and it is driving me nuts and slowing my restoration !! thanks !!
 
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