SWR/Power are strange...

Check ohms from antenna bracket to body,
And antenna bracket to battery. If anything other than zero ohms you have found your problem. Swr measurements won't be accurate with a bad ground.

 

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Not exactly correct. Running a wire or ground strap from the antenna mount to the battery could very well act as another antenna. You are not grounding the antenna. What you want to do is called BONDING. Bonding is interconnecting the large metal surfaces of the vehicle together to create one large antenna ground plane or counter poise. It has nothing to do with electrical grounding. When your SWR measured on an external meter [not the SWR meter in the radio] is above 3, that is an indictation that your antenna ground plane could be faulty.
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. Using a multimeter [volt ohm meter] check the resistance from the antenna mount to the door. If high resistance, bond the antenna to the door using a short length of ground strap.
.Then check resistance from the antenna mount to the door frame. If high resistance, bond the door to the door frame using a short length of ground strap. To accomplish this, run a ground strap from a bare bolt on the door side of the hinge to a bare bolt on the frame side of the door hinge.
.Finally, check the resistance between the antenna mount and the tractor chassis. If high run a short ground strap from a bare bolt on the cab frame to the chassis.

 

I never told a guy to run a braided strap from his bracket to his battery. I simply told him to measure dc ohms between the two.
DC and Rf potential must be equal

 

Bonding shouldn't violate any company policy. Use existing bolts and make sure they have a bare metal connection. You can do this stealthily, just shiny up the metal under the washer, it doesn't take much. Keep your bonding straps under 18". Use flat braid or a piece of coax, or even a large gauge wire with a whole bunch of fine wires in it like they use in stereo shops.

Maybe, maybe not.......sorry, but you won't know until you try. There is a thing called "ground loop" that is not good too. I'll leave the explanation for that to someone else.

The 5ft long wire you referred to is an attempt at a bonding strap.....it's too long though. The only modification you are making is shinying up the metal for good connection, and they'll never know if you just do a small area under the the washer/bolt head......and probably won't care if they do see it. Inconsequential I would think. Remember, it is always easier to get forgiveness than it is to get permission!

 

Sounds like a radio problem to me.