Paul,
Best approach is to bring slide in and then reattach the brake to hold the slide in place.
The brake needs a full 12v+ to operate and the wiring from the switch the slide mechanism has a number of connections that can offer resistance. Try the slide after the generator runs a bit to ensure a full 12v. Also check the connections, especially at the slide switch. If wired like my 01 Contessa, the wire awg from the slide circuit is reduced at the switch pigtail. Also try un/re-plugging the connector on the switch itself as it can give you a poor connection.
If you want a block diagram of the wiring circuit let me know,
Steve