There are different styles of funkjam:
The guitarist plays with very low gain and reverb on the bridge pickup and a wah-wah pedal. The bassist plays clean with smooth, finger picked notes and can include some light slapping. The drums are light.
The guitarist plays with medium/high gain in either the bridge pickup of the neck/middle pickup. The bass plays with low gain and heavy slapping. The drums are very heavy with lots of cymbal crashes, in other words, the drummer has a spaz-out.
Red Hot Chili Peppers normally play a funkjam for the intro of their gigs.