Hi Sunchaser.....why do you want heated grips? Summer down there isn't it?
I tried to pull the cover out of mines, only because I wanted to adjust the angle of the handgrips. Looks easy in the "Book", remove one screw and everything should come apart.....not so, I could not even pull the cover out by more than 1/8". After some careful pulling and prying I managed about 1/4", just enough to squeeze a ball end wrench in there and adjust the angle of the grips.
But looking at it carefully then, it seems there is a screwed on clip to hold the wiring in place, with that removed you should be able to pull the cover/switch out. I had no reason to do that on my bike so did not insist.
But like Vox says.....a job for a jeweler. But with the cover pulled out a bit, you should be able to spray some contact cleaner in there, and then lube the switch with some good dielectric lubricant. Largo.....should be some marine suppliers there, always a good place to find such products.
I lived and rode BMWs for years close to a wet marine environment, every couple years I did lube all the switches and connectors with marine products and never had an electrical failure caused by corrosion. This bike I just bought had quite a few connectors showing a little corrosion, so I cleaned and lubed them all and did the switches also as much as I could within the limited space BMW gave us to work with....
Those heated grips are know to fail from the heating wire breaking inside the grip, that is repairable, I've done it before and some of the GS guys on ADVRider are also.I do not think there is a relay dedicated to the heated grips, there should be but.......!
If you have any kind of foam grips over the OEM, they will take a long time to heat up in cold weather, if they ever do.....
Testing them, you may want to find the connector(s) to the grips and see if there is power to them, I'm not home this week to look,but I don't think they go very far into the harness. You could also disconnect the battery and check for draw with an Ampmeter, however you either need a very good one with large capacity for that, or disconnect the headlight, fuel pump etc so as not to put too many Amps through the meter and fry it. Most of the cheaper multimeters are only rated at 10 A or so.
I've seen the Wattage on then grips before, don't remember, but the conversion would be Watts divided by Volts(12)= Amps.