Who doesn't love chasing down electrical gremlins? I don't. One of the major contributing factors to an ill performing bike is corroded contacts. Those bullet connectors are harbingers of corrosion. Oh yeh, over heated terminals as well, thanks to Suzuki's legendary poor charging system. Hopefully this page will help you with a few things. Make sure all your contacts are clean and don't expect to much from your thirty year old wiring harness.
Headlight / Relay
Clocks Repair PDF
Vapor / Katana Idiot Light Diagram
GSX-R L/H Control Upgrade Wiring Diagram
The 1982 and 1983 gs1100 katana do not have the exact same wiring harness. They have a different pin out placement for the white Molex controller plug that resides under the seat beside the blue Molex controller plug. If you install 1983 controls on a 1982 katana, you are not going anywhere unless your pushing. Don't ask me how I know or how long it took me to find out why I only had power to my rear brake light and nothing else. The plug coming from the kill switch and the signal control have a different pinout than the harness of the other year.
These are getting scarse. I like using SPA ($500.00) or Vapor ($150.00) instruments in place of the stock ones. I have posted the installation wiring diagram for the Vapor clocks above under the tab "tacho",for those who would like to try them. If you want to try and repair your stock Suzuki katana speedometer a friend of mine, Joey Hong, produced the instructional how to also posted above under "Tacho".
I am a resto-mod guy so like to upgrade many of the old parts. GSX-R controls are a nice upgrade. I have added hi-low pass and a headlight off switch by using late model GSXR controller. The kill switch is a very easy upgrade also. When using flatslide carbs you need to use a push/pull throttle which requires a slimmer kill switch assembly. My wiring diagram is above under the tab "Controls".
Dim lights are bad for a bike. Usually with these old harnesses, there is much resistance in the system so by the time voltage reaches the headlight, there is not enough to burn it bright. A headlight relay hooked directly to the batter helps this. Read the "How To" .PDF file above under the tab "Charging", thank you Matchless for the contribution. Excellent instructional.
LED signal require a low load signal relay to work. LEDs do not have enough resistance to actuate the relay.
The signal control module on under the left side cover is not needed for the signals to work. It is part of the auto cancel system. If that is not working anyway, or you don't care about it, remove it and save some weight and room.
Wondering if there is a better option than that old car battery your GS is carrying around? There is, I use and sell Shorai lithium iron batteries. The stock battery is 14Ah @ 190 cold cranking amps, 5.5" x 3.5" x 6.5" and 4.6kg. The Shorai lithium 14Ah is under 1kg, 4.5" x 2.25" x 3.5" and has 210 cold cranking amps. The one I use is 18Ah, 270 cold cranking amps, 5.83" x 2.63" x 4.13" and 1.05kg.
I take my battery out for the winter and just leave it in the basement at 13.6v and the voltage will stay there for 6 months. With proper maintenance the lithium can last 8 years or more compared to the acids I replaced every 2. Liked them so much I became a dealer for them.
These old charging systems are not the best. I use Compufire regulator/rectifiers on my bikes. They are the only reg/rec I have found that don't cook my stator and drop my oil temperature significantly. I like them so much I sell them.
If you are having problems with your charging system, there is a charging fault finding flow chart from Electrosport Motorcycle regulators/rectifiers above under the heading tab "Charging". Very helpful. Before I moved to the Compufire components, I always upgraded the stock reg/rec to the electrosport.