Weird Vacuum pump with tach sensor help?

[Valor]

That is the same tach that I plan to use in my new gauge panel. Because I am swapping the TH400 for a 700R4, I won't need the vacuum pump anymore, so I installed a HMMWV oil pump drive with tach sender on top. It seems pretty simple to hook up, 24v in and 24v to ground, with the 2-wire signal from the sender going to the other 2 posts. Are you planning on keeping the TH400 transmission which requires vacuum?

View attachment 840096

I already have the 700R4. The vehicle is a civy suburban. I'm wanting to keep the vacuum pump for the HVAC controls as they are vacuum operated. Just trying to get a tach to work in the thing. I also have one of those ess sending units for the HJMMVEE. If you ever get yours hooked up and working, could you please share your wiring setup? Thanks.

 

[Valor]

Wow I just refreshed an entire year in 20 minutes from my electronic schools 40 years ago.
Thanks

Yeah! When I took electronics in high school, we were learning how tubes worked! Transistors were a new thing!

 

[Valor]

C. When the transistor is on, collector voltage goes to ground. When off, the voltage is to the rail, through the 1k ohm resistor. This resistor value is based on the impedance of the tachometer.

What would be the impedance of the HUMVEE tach? Could I just measure the resistance between the signal + and - input points on the tach and call it close enough?