This pinout is the result of considerable painstaking experimentation and deductive logic on my part. I hope you enjoy it.
If you have occasion to troubleshoot the wiring of a Volvo 240, you may find yourself tempted to disassemble the ignition keyswitch connector to find out exactly where all those wires lead. I advise you not to do this without the appropriate wiring diagram for your car's model year. After removing the rear shell of the connector by pulling back on the three plastic tabs, you will see that the wires are soldered into cylindrical metal sockets which fit into holes in the bakelite body. As soon as you feel confident that the sockets will stay in place without external fixation and slacken your grip, they will all pop out of the connector into complete disarray.
Cursed be Sven! For Volvo used the same connector with the same markings on the 240 and 740 series across decades, but seems to have changed the color code and connection of the wires with each successive model year. The only diagrams I had available were for 1976/83/86 240 and 1987 740; in each diagram the pinout for the ignition connector was completely different and none matched the number and colors of the wires in my sweaty fist.
So, after a bit of continuity testing and hair-raising experimentation, I arrived with the working pinout you see before you. I have placed it on the Internet for all to see, that someone may hopefully benefit from my misery.
Just for fun:
*Actually, a fairly low eventuality, unless I have to do this again and find some more broken meters. Suffice it to say that the platinum filament and other component parts can be swapped between meters with some trouble. Feel free to email me for details.
Contact: reboots at g-cipher.net