I have been selling Reatta parts for 25+ years and always learning something new. I've discovered the 1988 heater programmers are different from the 1989-1991s.
Yesterday I was using an '88 parts car to test programmers from other Reatta parts cars. The original one in the '88 tested good. The two I took from a couple of '90s would not change the air direction from floor to defrosters. Seemed strange that two of them would not test OK.
I then got an '89 parts car and tested all of them again. Now the two I took from '90s worked in the '89 but the one from the '88 would not change air direction.
I am guessing over the years I may have thrown away some good programmers thinking they were no good when in fact I may have been testing '88s in a '90 car or vise versa.
I compared the wiring diagrams in the shop manuals from '88 and '89 to see if there is a difference in wiring. One example of the differences is the ppl wire from the BCM going to the programmer. Inside the programmer it goes to resistance 5V battery in the '88. But it goes to resistance ground in the later programmers.
Thanks to Jim Finn for this information.