Can I see images of where the plug is under hood for Cruise control connection on 2005 GMC?

obd II fuse located ???? Or do you mean fuse for DLC - the connector under the dash that you plug the scan tool into ? GIG LTR fuse 15 amp under hood fuse box

Do you have a air bag light on the dash ? Check ground circuit for lose connection . Ground G203
In the I/P harness, on the left side of the I/P near the A-pillar below the I/P top cover .

Check the wire connector that plugs into the cruise control under the hood. Sounds like a loose connection. Remove the and reinsert the wire connector several times to make a better connection. Stepping on the brake pedal disengages the cruise control by a switch on the brake pedal, not the computer.

It may be in the fuse panel under the hood. If it is ok, check the cruise control kick out switch operated by the brake pedal. If mis adjusted or knocked out of position cruise will not work.

If you don't have wiring diagrams,can't read them,&
or work on your own vehicles & their technology,then
a repair shop or different dealer, is you only option,that
question you knew the answer to

check vac. connections under hood as well as a signal to the cruise cont. head check for signal out of cruise switch are your brake lites sticking this will cause the cruise not to engage their are also this circuit is fused

try and check all of your fuses, under the dash an under the hood, If that don't work then you will half to replace the swich.

Locate the switch under the hood and clean all the connections

Sounds like you have a bad ground somewhere. Get a voltmeter and start probing around and wiggling connections, like the battery to engine and frame.

most likely just unused wire, did you check the fuses, check them inside and under hood.