The general idea is to gut an old Dell Optiplex GX270 and stuff the high-voltage parts of the sewing machine controller inside a well constructed and solidly grounded metal shield inside a not-too-ugly plastic box. It’d be nice to reuse the power control button and status LEDs on the front panel…
The few parts on the front of the through-hole board:

The copper side, with annotations:

The red tracer on the ribbon cable goes to Pin 1, which is a blind key on the PCB.
The LEDs do not have ballast resistors, so those must go on a circuit board somewhere else.
The connections:
16 | 14 | 12 | 10 | 8 | 6 | 4 | 2 |
Gnd | nc | nc | nc | nc | HD+ | HD- | Button+ |
Gnd | nc | Gnd | Pwr Y+ | Gnd | Pwr G+ | Gnd | Key |
15 | 13 | 11 | 9 | 7 | 5 | 3 | 1 |
Sigh. Integrated resistor LEDs never fully caught on, though we sold a bunch of them over the years. They solved a lot of problems, but the marginal price increase hurt. (That, and they weren’t very compatible with dual-color lamps.)
A fixed resistor restricts the input voltage range, so you must stock half a dozen different “identical” LEDs. Only one or two of those would sell enough to make their premium price worthwhile, while the rest lingered on the shelf until they turned into weird surplus items on my shelf.
I’m sure they’re still made for extreme high-volume users. Those are the same users who care desperately about the cost difference between a fancy LED and an 0201 resistor, so maybe not.