Chevrolet Repair: 1988 Chevy 4X4 Silverado 1500, chevy 4x4, amp fuse

Question
I have a 1988 4X4. during the last snow storm I shifted the transfer case into 4 Hi and about 5 seconds later I lost my heater motor and my 4 wheel drive. I replaced the 20 amp fuse and all works well until I shift into 4 wheel then I blow the fuse in a few seconds.  Any ideas on where to start troubleshooting? Thanks for your advice.

Answer
Here is a link to an upgrade for the 88 style.

http://www.getdieselpower.com/misc_auto/actuator_upgrade/GM_TRUCK_4X4_ACTUATOR_U...

Van