Been pokin around lookin at various parts on E-pay for a tach for the big ol beast. I'd really like to find a factory part, but I've pretty well given up hope there.
I found myself a 12V 6-banger signal generator for a Sun Tach. Was wondering if anyone has adapted one of thier tachs to fit in the right side hole on the stock GMC dash panel & had some pictures?
Just interested if anyone else had gone that way as it seems to be where I'm goin with this part of my insanity.

A built in tach that fit in the right hole was an option on a 450 series and larger. 450 used a 302 6 cy. 550 and 600 series used a V8. From there on up the gas burners were the big 6 cy engines like the 503.

I got my truck with a sun tach already mounted into the opening. I rebuilt it & installed a matching face identical to the speedo to make it look original.

Thats pretty uch what I'd like to do, not a real fan of mounting it on the steering column.

The Sun electronic tachs that were used in the 1950's and early 60's had a sending unit that looked like a big voltage regulator, with a brown Bakelite cover. I believe some of them were dealer-installed as an option on medium-duty trucks back then. They used a set of Mallory mercury batteries in an oddball voltage, and those batteries went obsolete many years ago. I've seen original-appearing systems that were actually rebuilt with modern electronics, but I don't recall what company was doing the conversion.
Jerry