Isuzu NPR box truck questions

I just got a nice 86 NPR diesel 5spd box truck for an upcoming move. I got it cheaply enough that I know I can get my money back after the move, but I'll probably keep it for moving machinery and such.

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I have a number of questions.

Is there a good online place where I can order parts like filters and manuals?

The right hand stalk controls the wiper (which doesn't work at the moment) and you lift it to control something else. See the last pic in the above site.

I can't figure out what the little symbol is. You lift the lever to turn on and off the mysterious green dash light with the same symbol. Exhaust brake maybe??

There is another mysterious knob on the dash with a square containing a slash and surrounded by a circular arrow.

Thanks for any info or knowledge you care to impart on these trucks