Stinson pilot reports radio failure while waiting to depart Sun N Fun and signals this fact to the Controller at the runway end. The Controller responds with a rapidly rotating arm signal which the reporter assumes to be a takeoff clearance and does so.

Narrative

When taxiing to line up and wait for departure at Sun n Fun; my radio failed completely (only one working radio) due to what appears to be rain water falling down from my panel and shorting the radio contacts. My airplane is always hangared; but it had been left outdoors for the week during the heavy rain that occurred at LAL. The radio had picked up the ATIS; although with squelch and static and was probably working until I turned a couple of times to line up; where it made a squealing noise and loud static noise and then I was unable to hear or transmit. Water was dripping in the cabin from above the panel. At the Departure Controller; I pointed to my headset to indicate a lost comm and the one of the two persons on the departure stand used a rapidly rotating arm signal that appeared to indicated to me to GO or depart. Since the NOTAM says follow red shirted personnel instructions; I then departed. I believe the controllers should have light guns so that when there is a comm problem; the light signal could be used to give me a better departure or a light return to the starting point; rather than a hand signal.