[dmjlambert]

You've got me puzzled about several things. I've never heard of needing to replace an alternator because it was magnetized on the front. What is that like? Was it not working?

Were you replacing the original alternator that requires the external regulator with an internally regulated alternator? Or replacing with another alternator just like the one you removed?

Have you also replaced wiring on the truck?

You also said tach does not work because the wire that is unplugged goes to the ignition. I don't see how the tach could be related to a wire plugged or unplugged at the alternator. You should be able to completely remove the alternator and all connections, and run the truck and everything will work except battery charging. So you really have me puzzled there and I think others may need to help with that one.

It would be good to see some pictures of what you have. Front and back of the old and new alternators and any custom wiring, and what is the wiring like at the regulator, and any jumpers you have at the regulator plug if you use an internally regulated alternator.