85 GK71B...

oscillating temp needle - gets more vigorous with engine speed - as in full extreme - so fast it's a blur back and forth
Seems like some AC signal is getting through and causing it to oscillate - maybe a bad rectifier?
checked battery charging and still seems ok there.

Any ideas?

Also finding random moments where all lights die, and come back on randomly later on.

Could be the reg/rec on its way out or possible its a short and the temp gauge could be picking up the rev counter signal.
Have a good look around the connectors and where the loom bends around the head stock.

ok thanks rev counter pickup is a good suggestion.

I've been tracing the wiring to find the general lights out fault, and found the rectifier when tested according to the manual shows no circuit beween ANY of the terminals - the manual says any multimeter besides a suzuki tester won't give the correct reading but I get nothing on ALL of them... wonder how my bike has been running/charging all this time if it hasn't been working? I'll post another question for the rectifier

for the record to help others-
found the problem behind the instrument cluster - btw it's much easier than I thought to remove the front fairing - a melted connector (prob from some shorting of the battery teminals at some point ) was allowing temp gauge and tacho to touch/interfere.

thanks for the advice