1999 Hyundai Van speedo stops working sometimes, hold ligh

The "HOLD" light on the instrument panel begins to flash sometimes when the hold switch for the transmission is not even turned on, normally when you use the hold option on the transmission the light on the panel would just illuminate without any flashing, it has done this twice now in the last two weeks and at the same time the speedo stops working, like the needle just drops down to zero. Both times its been raining, then I stoped the car and turned off the motor and restarted and it was back to normal, there is no problem with the transmission it works fine, its been serviced as per log book by hyundai.