there is a main connector block located on the underside of the steering collumb that may have leads that go to the indicator panel. wiggle it and see if that helps. its really tricky to get to the back of the panel itself to see if there is a bad connection there though. because the fule tank leads run from under the bed, but the temp gauge is on the engine, it may not be the senders that are faulty. but check to see if the temp lead has come loose from the sender. also pull the lead loose, and check the resistance from there to ground, while a helper keeps an eye on the dash indicator. this sounds like open circuits, and two seperate problems.
that said, the previous reply is a very good one. and auto electric problems are often the hardest to troubleshoot or fix.
unfortunately, toyotas color coded wire diagrams in chiltons and haynes are not at all reliable. and they did some weird splicing moves to save on the lengths of wire.