I assume the car is a MK2 (A2) It depends is the car CE1 or CE2?
On a CE1 vehicle the hazzard switch is a rocker switch on the dash, where as a CE2 the hazzars swich is on the steering collumn, as long as both the vehicle your fitting the clocks to and the vehicle donating the clocks are the same CE1 or CE2 its dead easy, just plug and play, as there already is a revcounter feed present for the oil pressure warning buzzer, and asif Volkwagen would make 2 verions of the CE1/CE2 dask loom IE one for rev conters and one for "big ben" dashes.
I have fitted a A3 CE2 TDi set of clocks and stalks to my A2 CE2 GTD, I also converted my A2 CE2 1272 Jetta LX to A2 CE1 GTi clocks and A3 MFA stalks, so I know more than a little about VW dash looms.
CE1 clocks have two plugs, CE2 clocks have one plug, CE meand central electric, sometime arround 1989 VW decided to simplify the electronics accross the range so implement there CE2 standard which is still going, thats why a 1.8 20VT engine loom can plug into a late mk2 fuse box, and a set of mk 3 stalks can plug steight in on a late mk 2 column loom.