I don't see what year the truck is but on my 94 the solenoid pull up coil is fed directly through the relay by a fusible link from the driver side battery. On later years I believe the solenoid is fed from a fuse in the power distribution center.
Is this one of the frequent problems caused when the starter sticks? If so, did you get a protective diode from Larry B? If not, you should. It would be good insurance. You can get the large diodes elsewhere somewhat cheaper but Larry's offering is a kit that makes it easy to install.