compressed air (if you have a fine bristle brush that will fit in those small spaces that might work ok too)
do not use water period! no degreaser either

you can use motor cleaner or contact cleaner
anything that will evaporate quickly and is designed for cleaning electrical components or motors.
Just make sure you unplug the battery and discharge any capacitors on the panel if any. Alot of times pressing the horn will discharge any residual power stored in any circuits.