It works just like the newer ones, but you can't turn it off. It's 2wd until the rear wheels slip, then the hubs lock and you get 4wd.

Here's the one we have:

 

unplug the black wire from the rev box. its under the hood peice and if your standing infront of the bike lookin at it it will be on the left side of the frame. small black box..

and never ever run one of those motors without the clutches installed. you can over-rev the motor and destroy it completely.

i would definatly take the carb off and do a complete disassembly/clean job on it

 

Turned out to be an electrical problem. the speed module was fine, but the reverse light, neutral light, headlight, and tail light were all out. The previous owner ran it without a good battery. They guy i brought it to says that the reverse light is wired into that speed module and that is why it was stuck on.

On a side note. Everything is now great. The bike has some serious white smoke coming out of it.

 

yeah the 4wheeldrive is full time

 

He bud.. I had the same problem with my 87 and it was the cdi box..apparently it is a common problem..