that sure wouldn't work on the newer trucks. It's all controlled by the ECM. I've inquired to Mike at Isspro about some sort of control box to integrate with the tach. He said by next year they may have something. So far, as far as I've seen, no one makes anything that will work. A mechanical truck it just may work on.
You could probably use a dakota digital box like this one connected to your alternator. That will give you the pulsed signal to run an aftermarket tach like an autometer with a shift light.
Here's how I connected mine to my alternator on my 3rd gen engine.
My Dad uses one of these and they work well. He had them build a voltage amp or something like that to get everything to work properly. It works very nice and is compact. Lon