My experience with aftermarket sending units is that they are very inaccurate. I have tried a few of them and their resistance values are off from the factory ones. I have only tied them into the factory gauges though, and the last one I had read way too hot. I then found a used factory one in an old intake manifold, installed it, and it fixed the problem immediately.
I would highly recommend Barry, but plan for a couple months to get it back. He has done both a '66 and '69 8-track for me, did a wonderful job, and I have a 2nd '69 8-track at his place right now getting fixed. He takes his job very seriously, and is the only person I would trust fixing these units. As far as button interchangeability, unfortunately these buttons are kind of rare (I may have one if you really are in a bind - PM me). Here is a good reference for the radio's you need to get a button from, and I got it from the following link:
The Motorola part number is 38-41329B01, which is used on the following AM/8-Track players:
T8MM - 1968 Mercury
T8MZ/T8MZW = 1968 Mustang/Cougar
T9MZ - 1969 Mustang
1MZ4004 - 1970 Mustang
1CR4005 - 1970 Cougar
http://forums.vintage-mustang.com/vintage-mustang-forum/485579-radio-push-button-interchanges.html
mqu02 got a reaction from mwye0627 in Which Temperature Sender is Best
mqu02 got a reaction from RPM in AM/8-Track