Okay, here's what I discovered in my early morning attempt to figure this out...

Legend:
TS = exterior turn signal lights
TSI = dashboard turn signal indicator light
4W = exterior 4-way emergency flasher lights
4TSI = dashboard turn signal indicator when the 4-way is in use
4WS = light in 4-way flasher switch

NOTE:� There is some PO-crafted wiring in the fuse box, along with my own for the GW headlight upgrade, but none is new and there has been NO change to anything electrical since I replaced the high-beam indicator during the summer.

IGN OFF-Headlights OFF-21 Relay IN
TS = NO
TSI = NO
4W = YES
4TSI = YES
4WS = YES (in sync with 4TSI and lights)

IGN ON-Headlights OFF-21 Relay IN
TS = YES
TSI = NO
4W = YES
4TSI = NO
4WS = YES (in sync with lights)

IGN OFF-Headlights ON-21 Relay IN
TS = NO
TSI = NO
4W = YES
4TSI = YES
4WS = YES (in sync with TSI and lights)

IGN ON-Headlights ON-21 Relay IN
TS = YES
TSI = NO
4W = YES
4TSI = NO
4WS = YES (in sync with lights)

Very simply, with the 21 Relay out; nothing, nowhere, nohow.

IGN OFF-Headlights OFF-21 Relay OUT
TS = NO
TSI = NO
4W = NO
4TSI = NO
4WS = NO

IGN ON-Headlights OFF-21 Relay OUT
TS = NO
TSI = NO
4W = NO
4TSI = NO
4WS = NO

IGN OFF-Headlights ON-21 Relay OUT
TS = NO
TSI = NO
4W = NO
4TSI = NO
4WS = NO

IGN ON-Headlights ON-21 Relay OUT
TS = NO
TSI = NO
4W = NO
4TSI = NO
4WS = NO

Thanks for taking a swing at this, guys.

Stephen