Tachometer still cuts out

The tachometer in my 2000 Sonata (4 cyl auto) periodically stops working
now. It just sits at 0 rpm. Then without warning it starts working
again, and visa versa. Typically, when the car is started cold, it works
for a while, then cuts out, then comes back on and stays on.

I just had the front brake pads and rotors changed.

I also had some work done on the timing belt recently.

(see my earlier threads)

Could this type of work have some how affected the tachometer?
The tach trouble seemed to start right after they had poked about with
my timing belt(s).

 

There's really no-one here who has any thoughts on why this is happening?

For the record it's stayed on for the last few days.