What's this supposed to go to?

[Highway_Glider]

Thanks Highway_Glider. So, curiously, if I had the optional radio, is there an optional cable that connects that connector to the battery somehow?

I don't really know how it was supposed to work. Never seen an OEM radio on a GK. Car radios, yes. OEM, no.

I always assumed (And never went any further) of some kind of remote operation of the radio with a few switches on the handlebar (Like volume plus-minus and tunning plus-minus).

From MCS about the GS1100GK:

http://www.motorcyclespecs.co.za/model/suzu/suzuki_gs1100gk%2082.htm

In the middle of the text:

It has removable lowers, built-in front turn signals, a headlight-adjustment knob in the cockpit for the rectangular headlamp, locking storage pockets on each side of the interior, a non-locking compartment on the right, and removable panels to permit installation of the Clarion radio, speakers, etc. to be offered in 1983.

Both my GK and my donnor GK were manufactured in 83. My manual taken from Basscliff's website is from 82 and the diagram doesn't show the connector. So maybe the 82 doesn't have that extra connector.