Can't help with the bulb number but surely someone else will be able to post it. For what it's worth, in 53 and 54 it was #1133
Back up lights were optional and until 53 when some common options started becoming more standard and made it onto the basic wiring diagrams, Packard usually provided option or accessory wiring only with the instructions on how to install the option.
I do not know who originally posted this info but here are the instructions for installing back up lights on the 22-23 series. Packard shows power coming off the tail light terminal of the headlight switch which would mean they will only work at times when the parking or headlights are on.
Attach file:
22-23 Back Up light install 1.jpg (265.68 KB) 22-23 BackUp light install 2.jpg (179.36 KB)
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