Here is what I did to run a new wire for my new SR5 dash on my 92 2wd pickup 4cyl. My dash was not wired for dash so it did not work when first installed. Got the dash cluster with tach from a 93 4runner v6 automatic. Also used the 4runner oil pressure sender needed for new dash oil pressure, screwed right into 4cyl block. See photos for locations, on the location to hook up the new wire if your tach does not work. The diagnostic port is under hood next to fuse box.

 

When initially wiring my tach, I attached it to the cluster in the same way, with a ring connector on the screw. But whenever I had to remove the tach I found it irritating to have to remove that connector from the screw. So I just soldered on a pin (clipped from the junkyard) that clips in the appropriate spot in the connector to the cluster. This provided a much neater and more "factory" connection.

It's just the little things like this that make me happy...

 

So does that little port then send the tach signal? I bought an aftermarket LED one that I never got around to installing, and I never looked it up where the get the signal

 

That signal is the IG- signal, which is output once each time a spark is generated, I think (or once per revolution, but I think it's the former). At any rate, it's a signal who's rate is proportional to rpm, which is exactly what a tach needs.

I believe it goes 0-5V, but I'm not 100% sure on the level.