My experience with an old M20 engine......
cover your distributor with a plastic bag, use a degreaser ( spray in can type ), use a brush for the stubborn stains, let it soak and then rinse well ( using ONLY low pressure water ). Yeah avoid the fuse box and after hosing down, please ( please x 3 ) use compressed air to blow off water from spark plug sockets.......to prevent misfire later from short circuiting. ( this is mandatory )
I will NOT allow car wash boys to do the above, only myself cos with old electrics and socket fittings......water ingress can create havoc - misfiring, erratic idle, improper running!
Oh ya, starting your engine and let it idle to dry off the wet bits AFTER pressured air drying is also helpful, though no mandatory.
Well, above works for me - but maybe cos my car has less electronics so wash at your own risk!