.. Rocker switch with center pilot light on dash does not come on, but "feels" fine ..
Owners manual shows Rear DEf fuse shared with other things that work, so can't be the fuse...
The rear window 'lines' all look fine/unbroken.. Any thoughts??

 

Have you tried bypassing the switch? With the switch on/bypassed, does the connector at the back window get power?

 

Easy solution: Get a replacement switch from a donor car (wrecker) and see if that makes any difference. Electrical switches do fail. This is a good time to do the repair with the (hate to say this) fall/winter season approaching.

I've run into situations like this before. Everything else on the circuit works. Just about always turned out to be the switch or a bad connection. Check the connector too to make sure it's not oxidized. Probably isn't but it's an easy check.

78/79 Ninety Eights/ Eighty Eights and Custom cruisers should share the same connector and switch when you're looking for donor cars

 

Where's the connection at the window? ..
I looked in the trunk & didn't see anything ....

 

The electric defog on glass has connections inside the car at the bottom left and right of the rear window. You need to remove the inside rear window trim (probably sail panels too) to access those connections.

They probably aren't the problem though. More likely its your connection at the on/off switch and the connecting plug. That should be really easy to access. The r.s. dash is only held by 2 phillips screws, the radio ***** and spring clips on the back of the plastic panel. Once the panel is off, the defog switch is held on by 2 (I think it's 9/32) bolts. Comes out real easy.