I own a 1995 Jeep Grand Cherokee and experience the "4WD Switch requires servicing" warning on a frequent occurrence, usually when the car is warm and hitting a bump in the road. The local Jeep dealer's service manager told me the problem was either a defective switch, which they replaced for $86, or an internal malfunction of the transfer case which would cost about $1800 to repair. The switch replacement was a waste of money; the Light came 'ON', on my way home from the dealer.
My findings: If the wife kicks the center console 'hard' the light will usually go out. Proves to me my problem is inside the car, not the switch, transfer case or external wiring.
For those of you that are receiving the 'Tail Light Warning' I may have some good info for you. The 3rd Brake Light, the one located at the top of your back window has three small bulbs, and in my case one of those was burned out, but not noticeable during a visual brake light check.
I have also had this 4wd switch problem. what i did was put the trans in N. N transfer case then 4L then 1st gear and went forward a couple feet. then N on the transmission then rev while still in 4L. then putting the trans back in N then the transfercase going from 4L N then Full time 4wd then putting the trans back in 1st creeping about 2ft then R 2 feet, shut the jeep off then restarted it and it hasent come back on since. i dont know if that would work for others. also disconnecting the battery but that was after i "fixed" the 4wd switch problem
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