I opened the system and traced the problem to the tape deck. The
inputs run through the tape heads and would only operate if the tape was
running. Found two problems with the deck:
1. The main belt was far gone. I changed the belt but it still didn't work.
2.
The multi-switch operated with the tape buttons was faulty and didn't switch the input to aux. No cleaning
would redeem it so I bypassed it and mounted an extra switch to the front
where the mic input was.
Works like a champ now and a round black button doesn't stand out too much. As an added bonus the tape doesn't have to be running when using the aux input.