Browse Category: Electronics

Indicator lamps

Ground (GND) to the lamps:

For the rear lamps the GND is not any issue. The indicators are mounted direct into the frame.

For the front indicators it’s more difficult. On my GT750A model the head light house is all metal and clamp GND direct to the headlamp bracket. On my GT380J it’s different. To make a proper grounding I solder wires to copper spacers and they were both connected to the GND wires inside the head light.

Wires from the spacers connected to GND.

Green wire (right indicator lamp) Black wire ( left indicator lamp)

All indicators worked fine, + the instrument lamp as well πŸ™‚

Looks like all of the electronics are working fine without any smoke πŸ™‚

Rear light

Making wires for the tail and brake lamp:

White wire: Brake

Brown wire: Tail

Black / white : GND

Wrapping the wires using textile tape.

Cable layout:

Decided to lay down the cable as shown in the picture.

Tail, brake + left and right turn signal.

Handlebar switches, left and right

This is what I had. Two right hand switches (one old and one new ) + one old left hand side switch.

Decided to mount the new one and restore the right hand side switch.

The overhaul process:

Important step: Take a pictures before disassembling the parts. Note, the clip shown by the arrow is mounted the wrong way. In that position it will short the headlight high beam to GND.

Primer painting.

Black paint + text painting.

Cleaning and polishing all electrical parts:


Lower part switch assembled:

Upper part switch assembled:

Almost done:


Done: Made a 9 pins connector to fit the wiring harness in the headlight.

Right side switch:

Front brake switch

Don’t even think about it, assembling the brake switch from below. The the spring will jump away along with rest of the small parts.

Turn the brake lever upside down. This is valid for GT750 as well.

I know, the nut and the bolt for the brake lever is wrong. Will be replaced later on when I get the parts. I have to use what I have to get going.

Make sure the switch moves freely to both positions.

Add the contact disk of the switch.

Mount the plastic enclosure and make sure you have a good strain relief.

Zip ties

I use reusable zip ties at this stage for an easy adjustments if needed.

Instrument lamps wiring

This is what I had… not good at all.

On the J-model all wires are connected with individual connectors as shown in the diagram below.

On the wiring loom I bought brand new, it’s different. One blue 6-pins connector + two separate connectors for the speedometer lamp and the tachometer lamp.

Since I have all the tools to make the mating connectors I decided to make a new wiring loom for the lamps. The old one was anyhow in a bad shape, but what about the rubber sockets for the lamps?

Was able to buy metal part of the sockets and designed the rubber parts in two pieces, 3D printed them using rubber resin and mounted it all together.

The photos below shows the process:

3D printed rubber parts:


Old and new. Will use standard bulbs, not the LED type as shown in the picture.

Crimp tool:

The picture above shows the lamps with the correct color coding. I used a very soft multi strand wire, but was not able to find the black/ white type. You have to be true to the color coding so I painted a white stripe onto the black wire.

The wiring loom will be wrapped using a flexible textile tape. That gives a solid but flexible wiring loom, easy to be fitted.


STL files for 3D printing:


Before and after refurbishing

The coil wiring was in a bad shape like the rest of the electronics. Wrong colors on the wires and missing connector.

If you don’t know how the coils and ignition is working, please have a look at my post i did 8 years ago when working on my GT750:

How to start: All parts were dismounted and cleaned. I was not able to clean the coils properly so I decided to paint them white.

The metal brackets holding the cables were sandblasted and nickel plated.

I had to use impact driver to loosen the screws. Don’t forget to use JIS tools ( Japanese Industrial Standards)

The bracket was sandblasted and polished.

All of the wires had to be extended or replaced. Each individual strand in the wire must be sanded before soldering. After soldering the joint was covered in epoxy and painted.

The other end of the wire got new terminal and was crimped.

This is the color coding and placement of the wires into the connector.

The orange wires are all connected to a common +12 supply and the placement on the upper row does not matter. On the lower row, it’s very important to do it right, if not the bike will misfire on wrong cylinders.

Mounted with new wires and connector.

Before mounting I also did a spark plug test to verify all of the coils. Connect 12V to the orange wire and short the other wire to GND( 0v). The body of the spark plug must also be grounded. When you release the wire from ground the park plug will fire. ( Just tap the wire on/off to GND and you will see the spark) Do the same on all coils to verify the function.

The resistance in the coil winding should be around 4,5 ohm. The current in each coil when grounded will therefore be 12V/ 4,5 ohm= 2,7 Amp. That’s the reason why you drain the battery very fast when leaving the ignion on and the bike is not running.

Wiring harness GT380

Hmm, a lot of questions but few answers.

According the the parts manual it looks like the wiring harness should be installed on the right side of the bike, or… not, right side must be wrong. I’m told it right is right, but based on feedback with images I have only got photos from GT380 owners with the wiring harness on the left side of the frame, and it’s the same on my GT750 too. The drawing above must a guidance of how the wiring are connected, not which side it’s fitted.

Based on photos I have got I have some idea about how it should be done. Some advice can also be found on YouTube, but you can’t trust them. Some might be right and some are wrong, and others are horrible wrong.

So, to summarize: I’m not sure, and in some case I don’t have a clue, but I have to start and will use common sense when I have to make decisions. I think a look at mye GT570 will be at a good help. As long as I make it all in compliance with the wiring diagram it should be fine.

Connectors and tools:

I bought a kit from China with a lot of different type of connectors + the crimping tool needed.

In addition I got hold of the upper and lower wiring harness and only need to make some few extra cables to fit into the harness.

The cable from the alternator is already done, please see my previous post. The same for the cable from the ignition electronics (the points )

Next up was the battery cable. That became a bit tricky. Was not able to find the old cable anywhere and how to make a new one. The corresponding connector is made of rubber and how can I make that ? Same procedure as before. I drew the part in Fusion360 and fired up my 3D printer with rubber resin. And here is the result:

I found a picture of the cable on internet and did the measurements on the mating connector from the wiring harness. After printing the part I glued the terminals and added heat shrink to the wires.

The STL file for printing can be downloaded for free:

Next step:

I inserted the main cable for the upper harness through the lower hole in the headlamp and the upper hole will go to the clocks and and switches on the handlebar. I will use adjustable cable ties for clamping the cable onto the frame so I can easy move and do changes as I continues with the wiring.

That’s enough for today. Will continue another day πŸ™‚

Another day:

Still winter in Norway and I will spend some time in the Man Cave to do some wiring:

Still not sure how to lay down the wiring, but I give it a try and use reusable zip ties for an easy adjustments.

Head lamp wiring loom:

Pushing all the wires back into the headlight house to free up as much space as possible. Will be a tight fit later on when the headlight shall be mounted.

Hmm, something is wrong… The blue connector is not part of the schematics. Can it be for a later model with gear indicator ? No, the color code is different.

Some minutes later: Mystery solved, see the picture below:

The blue connector is for all of the small lamps in the clocks. According the the schematic it should be individual connectors, not a common one for all of the lamps. Anyhow, now I know how to do the wiring. It’s more easy too with one 6-pins connector, but why is it not part of the wring ?

Phuu, for a while I thought the main wiring loom was wrong. Well, a bit wrong. It’s not the wiring loom for the J-model and not for the latest ones either. Not a big deal since I know how to wire it and have the tools and parts to make the mating connectors.

Instruments bulbs:

One of the bulbs sockets looks horrible, and the wiring is in a bad shape as well.

I think I order new sockets and make a complete new wiring. If so,I have to 3D print the rubber cover too.

When it’s done, it will be a separate post about how I did it. I can’t put this old and ugly bulb loom back into the lovely bike.

Clamping to the frame:

Photos from the wiring layout:

Tried to lay the wiring close to the frame away from the air filter and other parts to be mounted later.

The wiring loom is quite stiff and to avoid too much bend I ended up laying down the cable as the picture shows. Probably not like the original, but I think this will work fine. But doing so, the fuse holder will fit better on the right side, close to the tool box, but why not?

I will 3D print a bracket for the fuse holder. The fuse holder is not the original, but close to. A 20A fuse.


Make sure the threads are clean without any paint to ensure a proper grounding.

Less questions, all the wiring are now sorted out :

The upper wiring loom I bought deviate from any standard GT380 wiring, it has some extra connectors.

In addition to the 6-pins blue instrument lamps connectors there are two connectors with Gray and Black/white wires. for instruments lights ( tachometer and speedometer light)

One red wire with +12V, direct from the battery + pole and one extra GND wire. Can be used for alarm system or a charge port to the battery.

One green/yellow wire in the same connector going to the ON/OFF switch. Not in used for my J-model.

One brown wire. The same wire as going to the tail lamp. This wire will also be at power it the ignition switch is turned to parked position.

On/off switch:

The on /off switch is a bit difficult to spot on the wiring diagram, except from the GT380B wiring. The color code is quite simple. Orange is the +12V after the ignition switch (red before the ingnition switch). The orange/white is the +12V to the coils and the bike will of course never run if this switch is turned off. According to the GT380J wiring it’s the orange/white wire changes to solid organge from the switch connector and down to the coils, but not on later models. A bit annoying and I’ve seen several variants of the J-wiring diagrams. Not easy to know what is correct.

A summary of the color codes:

Red (R): The +12V from the battery through the 20A fuse.

Orange (O): +12V after the ignition switch

Orange / white (O/W) 12V + after the ON/OFF switch. Turn on /off the voltage to the coils. Note! only orange wire on earlier models (According to the schematics)

White (W) : Brake lamp wire.

Brown (BR) Tail lamp.

Gray (GR) Instruments lamps

Blue (BL) Neutral position switch. The indicator lamp will light if the wired is shorted to ground.

Light Green (LG) Right indicator lamp.

Black (BK) Left indicator lamp.

Black/white (BK/W) GND (Ground, connected to the frame)

Light Blue (LBL) Turn signal relay wire.

Yellow in the rear wiring (Y) 3 phase AC voltage

Yellow in the front wiring (Y) High Beam Head Lamp.

Note: The Gray and Brown wires will be shorted by the ignition switch in run position and both the indicators lamps and tail lamp will light (if the main light switch is on). If the ignition switch is left in parked position the orange and brown wires are shorted and the tail lamp will light (regardless of the main light switch).

Neutral Switch GT380J-K

The picture above shows the function of the neutral switch. The shifting switch (Part 44) is attached to the gear shifting cam. In neutral position the switch will reach the contact point inside the housing (part 39), this will lead to shortening the blue wire down to ground. Since the lamp in connected from the blue wire to +12V, the bulb will light up in neutral position.

Make sure the contact points are cleaned and polished at the inside and outside of the housing. I added a new washer and screw too.

Before mounting, put the engine into neutral position. Make sure the switch is mounted with the lip into the groove at the end of the shifting cam. If so, the contact point in the switch will meet the contact point in the housing.

To verify the function, measure the conductivity from the witch down to GND. Should be a short (close to 0 ohm) when the engine is in neutral position.

When you add the wiring harness, the blue wire from the alternator cable should be fastened to the switch.

Indicator Relay

The original indicator relay was missing on my GT380J model. A ugly replacement relay had been fitted, but was not properly fastened in the rubberband due to its square shape. I had to go on Ebay to search and found a round type of relay, a bit smaller compare to the real thing but looks nice.

Because it’s smaller I can’t use the old bracket with the rubber mount. I made a resin 3D printed bracket so I could use the rubber mount that came with the new relay. Like this:

Resin printed and cured with UV light.

The STL file of the bracket can be downloaded from the link below.

New terminals to the wire so it will fit into the original wiring loom from Suzuki. I also did a test of the relay to verify the function.

Important to use the correct color coding. Orange to the + wire (orange wire is the + battery voltage after the ignition switch) and blue to the indicator lamp. ( the casing of the indicator must be grounded. Note! the blue wire to the indicators will not be blue all the way to the lamps, please see the wiring diagram for details. The 2-wire relay is connected in series from the battery (after the ignition switch) to the indicator lamps. Controlled by the switches, left and right lamps will then get the voltage applied from the blue wire on the relay.

Mounted together with the rectifier and the regulator relay.

Note! The rectifire in the picture above is mounted different compare to how it came with the bike. I turned the recifire upside down and made a proper ground to the negative part of the diode casing to achive a better ground down to the frame. The + part with the insulator is therfore at left side of the picture. Please see my previous post about the rectifier:


The orange wire is the +battery voltage, but after the ignition switch. The green wire is the +voltage to the rotor and the white and black wire is the GND wire.

The regulator on GT380 and GT750 works in the same way. The purpose is to control the rotor current and thereby adjust the magnetic field so the generator (alternator) and rectifier gives about the same outputvoltage regardless of the rpm.

The case got sandblasted and repainted. The contact breakers in the relay were sanded a bit to achieve a good connection and the current flow was thereafter tested with a power supply.

The pictures below shows the different stages from 1-3 depending of the voltage to the relay coil.

The diagrams are a bit difficult to read, they are only meant to be a reference for the different stages in the pictures above. Details about the diagram and how it all works are explained in my previous post, the Alternator.

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