On the port side of the steering wheel just under the fuel gauge is a black screw cap w/chain attached.......does anybody know what it's purpose is?
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First nice cig, looks good in the other pics.

I am on the phone but that looks like a water fill? Could there be a tank in the cabin?

Use to see those for some kind of power outlet. Cap covers when not in use.

Either CB radio or some other kind of electronic port. Take the cap and see if it is .
RG

Usually a two prong power port for a Q beam spot light

Whatever you do , do not unscrew and open it ,, it could be a Portal to the other dimension .

Something added, that dash is not factory Mistress, so that's not normally there. Probably power outlet for something

Yea that's what it is so don't open it, let me open it.