There were differences in the compressors used on '88 model Reattas and the compressors used on the '89-'91 models.

The connectors used on the '88 models had a blade style male connector. The later models used a female style pin connector. There may be other differences in the compressors as well but for identification purposes this will be one major difference.

Thanks to Padgett for the photo

Thanks to Padgett, member of the Reatta forums, for this information.