Likely the switch. Is the steering column stalk used for other purposes
(like turn signals)? Over time these switches (single-purpose or
multi-function) get wonky. I had a car whose wipers would act weird when I
hut the turn signals...
The big problem is the degree to which the steering column has to be
disassembled to replace the switch assembly. If it's a multi-function switch
assembly, brace yourself for the cost of the new part...