I assume that the start was the click - click problem that is usually a short in the control head taking out the 8 volt from the main board.
After that was resolved I again assume that you had the 8 volt from the main to the panel and then the +5 and the +3.3 volt supplies alive and well.
It is possible that at that point you have another problem in the head. When the control head gets power the cpu sends a signal that it is alive and ready to the main cpu where the relay is not dropped out.
I suspect that a second problem was created when working in the head.
I believe the PWK signal makes a ground that pulls down the device that initiates the POWER ON SEQUENCE.
I would trace that signal to find out why the relay is no longer pulling in. PWK goes to the
IC1302 to initiate turning on.
The control head has no voltage on it until the relay pulls in.
The voltage present should be the voltage pulled down by the power switch. Check for that voltage on the switch at the transfer jack pin 2.
After the relay pulls in 8 volts at pin 1.
I hope memory serves and it helps you fix your radio.