It would most likely have been one of these:
This is an in-service shot of a '90.
I have more pictures of this type unit somewhere, they are of the one in the '90 that's currently owned by a guy (Louis D.) in NJ...I'll have to find them. I can't help you on ID'ing it, try the guys at copcar.com or Geoff Fors at his CHP radio history site.