The radio in my '90 740 was not displaying anything on the lcd, so I decided to swap radios with a known good radio from an '89 740 gle. The 89 has an equilizer. There are 2 DIN plugs on the back of the radios. In the car with an equilizer, there was a plug attached. In the other car, there was a plastic plug with no wires coming out. Apparently this little plastic insert does play a function in cars with no equalizer - without the plug the radio seems to be very quiet.

But the kicker is once I had both radios swapped, they both worked! Seems like there must have just been a loose connection. I guess sometimes it is not good to assume the worst.

-Nathan