[GTJIM (R.I.P.)]

Try Here ...

I have a 1991 Opel Senator - not had to fix the heater yet ... touch wood!

Most of the questions I have had are answered on this site:

vauxhall_senator : Vauxhall (Opel) Senator (all series).

Try a search for heater resistors - there are 15 'hits'!

HTH