The absolute best reference for wire colors, component identification, component locations, connectors, ground points, wire harnesses, and functional voltage paths is the Volvo Service Manual Wiring Diagrams green manual.

Here's a link to one for the 1994 940s which should be almost identical to your 1993, especially at the rear
https://documents.pub/reader/full/volvo-940-1994-wiring-diagram

You'll need to look at separate diagrams for park/tail/number plate lights (USA/Canada), brake lights (USA/Canada), tailgate wash/wiper, heated rear window and radio for the power antenna.

As you have a wagon with an in-window antenna, note that the power antenna line from the radio is instead wired to a little black box signal amplifier located at the base of the fuel filler neck. Additionally, in case you find any mystery wires, if you have a trailer hitch then the trailer connector wiring is usually spliced in near the left rear tail light and an additional power line for the trailer adapter is often run back up the left sill to either the electric seat connector or fuse panel, plus sometimes a line run all the way back up to the brake light switch at the pedal.

I thought coonhounds were a little less lunatic than that?
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now