Here's some pics that may help. The first two pics are from the 650 and 750 Brute Force. Look under your seat first and see if you have what's in the first two pics. If those connectors are not there, look for the other connectors down around the petcock.
On the connectors under the seat, take the gray cap off, disconnect the black connector and plug the gray connector in, and then turn the ignition on for about 7-10 seconds. Turn the switch off and reconnect the two black connectors, replace the gray cap, and stow everything back the way it was.
If your connectors are beside the petcock, disconnect the 2-pin connector and leave it disconnected, disconnect the black 4-pin connector and the gray 4-pin connector and cross connect them, and turn the ignition switch on for 7-10 seconds. Turn the switch off and reconnect all the connectors the way they should be.
If the belt light comes on again after performing this procedure, do it again, but this time while you have the switch on, tap lightly on the solenoid in the fourth pic. If this doesn't do the trick, then you will have to replace the engine cover with the solenoid made on it.
Scott