Tach installation?

[John Mc]

I've seen some folks have added a tach to their truck. Where are you picking up the signal for that? I've used a cheap digital display with a lead that wraps around a spark plug wire, but that was with the unshielded plug wire adapter. I'm not sure I want to leave that in the circuit while driving around. (I have the stock 24V military system on my truck, but with the Pertronix electronic ignition installed.)

I don't know that I'll leave the tach permanently mounted, but I'm curious to see what's going on with the RPMs during normal driving and how fast it's turning when the governor kicks in. I suppose I could leave the adapter in place for a bit, but I was not sure if that's a great idea for longer term use.

[NAM VET]

my truck is like yours, Pertronix, 24 V, OEM plug wires, and would like to add a tach too, so will follow this thread. Right now, I have an Autometer oil pressure gage, and a transfer case temp gage. hal, aka NAM VET.

[John Mc]

Where are you thinking of mounting your tach, Hal?

The cheap unit I have which we used for tune-up and trouble shooting does not even come close to fitting the look of the truck. I bought it to use the hour meter and tach function on a Coot I own (antique ATV), but have not installed it on that yet, so it was pressed into service when we were setting up the rebuilt 251 engine in my M37. I've not even tried to see if it can pick up through the shielded OEM spark plug cables. I doubt it will work, but I may try it. If it works, I'll just Velcro it into the glove box until I come up with a better solution.

I know some tachs work on a wire that attaches to an output from a modern electronic ignition system. I don't know if the Pertronix unit has such a connection, but even if it did, I'd have to figure out how to get the wire out of the military distributor.

[NAM VET]

Charles Talbert haș posted about a tach pick up at the flywheel, with some sort of switching for the tooth count. For me, knowing how my truck is running is more important than a stock appearing cab. For instance, here in SC , when my engine and oil is hot, I do'n't "load" my motor with cylinder pressure but accelerate easy and slowly as my oil pressure comes up, right in front of me on my steering wheel shaft. I don't want to put high cylinder/bearing pressure on my engine with an idle oil pressure. So far, no knocks or rattles on cold start. Oil pressure good. But on pavement, I can't turn my steering wheel, with NDT tires. Much easier to rolll just a bit forward and backwards. NV

[PoW]

There is a hex headed plug in the top of the distributor for the purpose of taking an electrical pulse sample for reading RPM.

Originally, there was an adapter provided along with the plug wire adapter. Some dealers sell that, called a timing light adapter.

The threaded hole is positioned directly over the coil terminal connected to the point set.

I've seen field taps made out of the stock plug by drilling it out and fabbing a spring-loaded probe to carry the pulse out to your tach.

PoW

[sturmtyger380]

spring-loaded probe

What is the probe attached to?

[just me]

The probe touches the coil switched side. (To points)