Finally something to report. As mentioned earlier, I always planned to add some gauges to this car. The first attempt, with an 80s electronic combo gauge, was an abject failure. After that, I took a while deciding whether to go with mechanical or electronic gauges; in the end I couldn't get over my dislike of pressurized oil being pumped into the cabin, so electronic it was to be.
From there I had a choice: spend real money for real gauges, or roll the dice on cheap Chinese units from Amazon. Cheap car, cheap gauges. I found a triple set with sending units included for somewhere around $25. As a bonus (to me) they were calibrated in metric units, something I've always preferred in European cars.
A lot of the work was done, as I had already run the wires into the engine bay. The main issues were feeding a signal to the temp gauge (more on that in a minute) and figuring out how and where to mount the plate (and doing whatever additional wiring that entailed). The 900 has a DIN slot down in the center stack, and I figured I'd either put the gauges there, or move the radio down since I rarely use it and put the gauges up higher in the dash. The latter was certainly more useful, but also entailed more work. It being cold in the garage this time of year, less work won. As it turns out, this was a better decision than I expected.
That decided, the first thing I did was figure out where I was going to get power for the gauges and the lighting, and make up the harnesses. I pulled the light circuit from the courtesy light in the ashtray, and the main power and ground from the cigarette lighter, both very close. I used spade connectors to make removal easy should it be necessary.
That done, I installed the new oil pressure sender (I already had a T-fitting in there from the last attempt) and wired it up. That left the temp sender. I measured a nearby heater hose as having a 22mm ID, which then led me to Amazon to find an adapter fitting (for motorcycles, as it turns out). The only issue with this is that the sender needs to be grounded, so I had to add a wire to accomplish that. I thought about tapping it, but the walls are fairly thin and I didn't want an additional potential leak source. Instead, I found a ring terminal that slipped under the sender, then cut a piece of fuel hose to act as a spacer and put some pressure on the terminal when the sender was tightened into the adpater.
I wasn't sure if this would work, but my multimeter showed continuity, so I installed it and hoped for the best.
In proper Roadkill fashion, I mounted the panel itself with a couple of zip ties. With everything back together, I started it up. The voltmeter and oil pressure gauge both sprang to life immediately. I also discovered that the internal lighting is provided by LEDs, and they are bright. And non-dimmable. This made me very glad I mounted them low and out of my direct line-of-sight rather than staring me in the face.
After a few minutes, the temp gauge also started to creep upward. That's all the testing I've done so far, but fingers crossed that everything holds together.
