[acastagna]

Problem sovled. Thank you to everyone who provided input. The issue was definitely ribbon contact with the solenoid board. Opening up the three side cars revlealed the same chip (U2) was burned. We did some testing and found that only a very light pressure was needed to make electrical contact with the cut end of a ribbon cable, which would send 24 volts into the side car. We tried the ribbon flush and taped the end with electrical tape, and everything works fine with a new side car. Luckily nothing else appears damaged.

So, the lesson learned is secure all possible points of electric contact.