While tracing some on-again/off-again headlight troubles to rusty terminals on the large, oval-shaped headlight DIP relay on the firewall, I noticed my reverse lamps light up when I tried the flashers (or, was it the brakes?)

So I know the lamps work.

Anyhow, after cleaning the contacts on that relay, everthing works reliably now, but for the reverse lights. They don't come on at all.

The poor wiring diagram in my Haynes manual suggests I am looking for a white wire where power runs through a switch and a reverse light relay (a relay separate from this headlight DIP relay)

Where are the reverse light switch and relay?

BTW, the starter is all reassembled, painted and turning over the engine. thanks, everybody! Had is running over half an hour the other night. Continuing to rebuild the brake hydraulics.
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'Don't Understand Why People Abort Volvos, Either'