Sparky,
Of course with no technical support, this is my best guess.
From numerous visits with them over the years, it is my understanding that the basic board set, which was used in all their products and modified for high precision, bigger cpu, more sensors such as solar or lightning, the wind sensor was one of three, chosen when you bought a unit from then, or returned to have them do a board modification and a ROM firmware update.
The choices were Texas Weather Sensor, R M Young sensor (the 5016 I believe) and the Texas Electronics type sensor, of the last version (was it a 114 or something like that?), and each was NOT interchangeable with the other.
I had most of mine changed to RMYoung (one came that way off eBay) and still have two with the TWI sensor package as the board-level wiring.
I asked either David or the other tech was went on with the mods (they charged me $90 plus shipping back then) and the best he'd say was some 'components' on the mother board were changed, a few jumpers, and a new firmware chip with code to do the wind speed and direction. They wouldn't divulge more no matter how sneaky I was in trying to find out.
I know the Young wind monitor uses an AC 3 pulse per revolution signal for wind speed and a standard potentiometer for wind direction. Their wind head uses an optical encoding, with pulses from a chopper disk for wind speed (sort of like the Heathkit ID-4001 and ID-5001) and the Grey Coding scheme (I think) for the wind direction, again very much like Heathkit.
The Texas Electronics earlier devices used a reed switch for pulse per revolution for speed, and the very expensive potentiometer for the direction, and that one could NOT be used for connection to the TWI boxes, since I had one and they said it wasn't a supported version. They needed the optical type, so much along lines the their device or the Heathkit type from what he alluded to, but again didn't go into details on the differences.
It sure would be nice if someone that had all the schematics and service notes would release them into the public domain for those of us trying to keep these things running to fix or modify what we could. If the ROM goes, I think that the whole thing will have reached the end of the line.
Nice stuff, good readouts with good visibility,and while wired vs. wireless, I have three running here right now and hope they keep going longer than I do.
Let us know if you uncover anything different, and if I've recorded something wrong here, please chime in with corrections to my note here. Dale