I was under the truck today replacing an o2 sensor and when I was getting back up I noticed a broken ground wire that connect from the bottom of the cab to the frame on the passengers side of the truck. It's obviously been broken for some time as there was noting left of the wire except two small sections where the blots are. I know it's the ground wire but what is it for and I need to know what gauge it is as I keep finding different options online? Thanks in advance!

 

Its a ground, so that's what it is for, so cab metal and frame metal have the same 0volts as battery negative

Cab and frame have at least 2 grounds maybe 3, they share
Use 14gauge or just get another ground strap about the same size