Horn question for 1977 Stepside

[77 ChevySport]

My horn seems to work about 80% of the time. I believe it is a ground
problem on the horn assembly. My horn is located between the radiator
and grill on the passenger side. My question may possibly be applied to
a great many other Chevy PickUps. Here goes:

What is the most simple and painless way to get to the horn to work on
it. There is very little room from the bottom of the truck to stick your
hand in there. I have jiggled the wire but would like to get in there to clean
the contacts better and clean the ground connection. All help is welcomed and thanks in advance. Larry

P.S. Everything checks out OK on the Steering Horn Buttom