Welcome to the forum Jethro.
I have a 94 Silverado, never heard of "mark III "
Fuse is a very good place to have power. Not Brake fuse, but Stop fuse.
Stop fuse supplies ABS, Haz flasher, brake switch(to brake lights and cruise),
and convience center(to chime alerts for key/lights)
Fuse is supplied from a fusible link connected at battery junction block on firewall.
That passes through bulkhead connector and, after a splice, goes four ways.
One to Stop fuse, one to ACC-BATT cb(lower silver can) for pwr locks, two to key.