Working on a 1977 bus and the nightmare of previous owners wiring for the stereo and booster amp. Below the fuse block (the standard location above the steering column under the dash) I found this larger plastic box than I expected. It sure seems like it's part of the fuse block: same black plastic, same size, looks to be part of it. But what throws me especially is the variable resistor knob as you see on the right side. It turns like any variable resistor like a volume control. It has no off/on switch at the end of the turning travel, it's just a variable resistor. But I have no idea what it does. The two white marks I'm thinking are there to show some previous owner the best setting to turn it to but that's a guess.
I'm attaching a photo. Anyone know what this is? None of my other buses have this (I don't think). Maybe some aftermarket fuse block and/or some addition or maybe it's stock from VW but it's new to me.
Thanks!
-George