It might be nice to get the original working if it is just a bad connection somewhere. If you want the ability to check the engine RPM while back there, instead of going to the cab to see what the fan speed is, to determine engine RPM, there might be a better and cheaper way.

Non contact, hand-held laser tachs are reasonably priced, simple and very accurate. I put one of each on my vari-speed mill and lathe. They come with reflective tape that you stick to the rotating part you want to gauge. You then point the red dot at the target and it reads RPMs as long as you hold the button on. listing on eBay here:

http://search.ebay.com/laser-tachometer_W0QQfromZR40