This is from Wayout440 on a taxi thread.

"Your solenoid multiplexing is broken...allowing power to both "A" (coils) and "C" (flashers) banks of solenoids. "When the bank select relay is energized, solenoid power V+ is connected to bank "C". Then only solenoids 1C to 8C can be driven by the driver transistors. There is no power available to bank "A". The "C" bank is usually reserved for flash lamps."
My guess is you have a short somewhere in or near K1 relay on the driver board, allowing power to both banks. When a solenoid driver transistor turns on, both the coil and flasher that are controlled by that multiplexed solenoid come on at the same time, because only one of them should be receiving power."

Seems relevant to your problem. Good luck.

Ok wel substitute K1 for A/c relay on Aux board. That as I stated came from a Taxi thread. And it fixed his problem. Its got to be a relay right? Can you pop open the cover and manipulate it with your hand? Maybe the relay isn't getting proper volts. Hook it up to a 12v battery see if you can make it work. Maybe your plus 12 v is low