1992 Cadillac Deville heater blower

Have you checked the EEC Power Module? With the ignition off resistance between black and purple wire should not be 0. If it is replace and recheck.
Turn ignition on. Simultaneously depress OFF and WARMER buttons on CP until "8.8.8" appears on FDC panel, and "-188" appears on CP. See Fig. 1 and Fig. 26. Code "8.8.8" appears as a check of all display segments and to indicate the beginning of diagnostic readout.
After display, "8.8.8" ends the segment check (approximately one second), and ".E "will be displayed. This indicates beginning of PCM stored trouble codes.
Following display of ".E, "lowest numbered PCM trouble code will be displayed for 2 seconds on FDC. All PCM codes will be prefixed with an "E".
NOTE: Trouble codes have an "E" (PCM) or "F" (BCM) prefix to designate which computer detected the fault. The "E" (PCM) codes will appear first.

Progressively higher numbered PCM codes, if present, will be displayed consecutively in 2-second intervals until the highest code present has been displayed. If no PCM trouble codes are stored, ".E "display will be by-passed.
Beginning of the second PCM trouble code cycle is indicated by an ".E.E"display. On the second cycle, only current hard codes will be displayed. Hard codes are malfunctions currently present. If malfunctions are not current, ".E.E"display will be by-passed.
NOTE: First cycle of BCM diagnostic codes (".F ") contains both hard and intermittent codes. Second cycle (".F.F") contains only hard codes.

After all PCM codes have been displayed, BCM codes will be displayed. BCM codes will be displayed in the same manner as PCM codes. All BCM codes are preceded by ".F "on the first cycle and"F.F"on the second cycle. See BCCM TROUBLE CODES table.
After all PCM and BCM codes have been displayed, or if no code is present, code ". 7.0" will be displayed, indicating system is ready for next diagnostic feature to be selected. See BCCM DATA DISPLAY
see pics