My plan was to take the sender wire through the firewall, but I couldn't
find anyplace that looked easy. But I did notice that the hood release
cable comes through at about the right spot. After pushing the rubber
grommet back a bit with a screwdriver, it was easy to fish a stiff wire
through the hole, and it came out at just the right spot under the dash.
I taped the sender wire to the stiff wire, but it was too tight a fit, so
I had to drill the hole a little bigger to get everything through.
The main problem was the sender wire was now pushed tight up against the
sharp edge of the sheet metal. I used electrical tape to make a pad and
stuffed it between the sheet metal and the sender wire. If that doesn't
hold up, I'll have to come up with a more permanent solution.
(DP: consider this grommet under the fuse box).