Back in one of my previous incarnations I was a field rep for Standard Ignition. At that time the local power company, HL&P (Houston Lighting & Power, aka., Houston Looting & Pillaging) was using big gas powered Ford trucks with BIG 2 way radios. They were using Standard's Blue Streak (heavy duty) version of Ford's ignition module to replace the OEM modules when they gave up the ghost. HL&P soon began reporting that if the drivers keyed the mike for their radio it killed the engine. Somehow the transmitters could set a RFI that could confuse the module enough to kill the engine. Standard came up with an internal shield for the modules that deflected the RFI. Problem solved but it took a bit of head scratching.