dual tanks -- need advice

[mdj3316]

The dual tank selector in my folks' 1985 Chevy has stopped working. The only fuse I can locate [in the main fuse block] is OK, the dashboard switch is apparently only removable from behind, I can't get behind the dash enough to either remove the clip holding the switch or get the wires loose [at least, not with any hope of getting them back in the switch block], and from the looks of the nuts attaching the cover over the main switching unit underneath [and what I can see of the unit itself], any attempt at disassemby will probably break something.

I would really hate to replace the main unit and then find out it is a bad switch -- especially since I still won't be able to figure out how to get the switch out.

Any bets on whether the problem is at the dash or under the bed?

How do I get the switch out, short of breaking it or cutting a hole in the dash?

Thanks!