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PostPosted: Mon Aug 20, 2018 10:08 am 
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Joined: Fri Nov 30, 2012 8:27 am
Posts: 89
Country: USA
Bikes owned: GT550
The PO of my '75 GT550 changed the gauge from the '75 style to the previous style and adapted all of the wiring for that. He replaced the connectors with bullet connectors and taped off a bunch of wires with duct tape, of all things.

I've changed the gauge back and when rewiring the male connector for the speedometer and tach lights, I've found that a wire was missing from the old gauge. In other words, there are five wires that connect to the old gauge for the lights, but the female connector on the correct gauge has six wires. The missing wire appears to be a black wire with a white tracer. So what's confounding me is that there are three random black wires with white tracers in my headlight bucket that aren't connected to anything. They were just taped off.

I'm gathering that these are ground wires, but where should they connect? And how do I determine which one should go to the connector for the lights? I've found the two wiring diagrams attached below, but I don't have any electrical experience. It looks like like there are only five wires connected to the gauge lights on the diagrams. Perhaps these diagrams aren't current for the '75? Any help would be very much appreciated!

Once I get that sorted out, I'll ask how the harness gets inserted into the bucket itself, i.e. which wires go through which of the two holes in the back of the bucket. If anyone has a photo of the guts of their headlight bucket, that might be really helpful!


Attachments:
GT550ColorSchematicsgoodquality.gif
GT550ColorSchematicsgoodquality.gif [ 199.95 KiB | Viewed 1436 times ]
Wiring Diagram.gif
Wiring Diagram.gif [ 78.49 KiB | Viewed 1436 times ]
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PostPosted: Mon Aug 20, 2018 11:28 am 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3416
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
Both of those diagrams are for an early GT550 with two taillight bulbs.

This diagram is for the later GT550 with a gear position indicator.
http://www.suzuki2strokes.com/forum/download/file.php?id=824

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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PostPosted: Mon Aug 20, 2018 2:29 pm 
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Around the block

Joined: Fri Nov 30, 2012 8:27 am
Posts: 89
Country: USA
Bikes owned: GT550
Thank you for that. The diagram shows a tachometer lamp. I wasn't aware that there was a light in the tachometer. What might that be for?

I can see now, that there are six wires leading to the gauge lights, one black and white that goes to the high beam indicator lamp. However, I still can't figure out how to determine which B/W wire it should be and what the other two B/W wires are for.

I don't have any experience reading wiring diagrams. It does look like there are B/W wires leading to the front turn signals, the tachometer lamp (is this lamp just to illuminate the gauge at night?), the high beam indicator lamp, as mentioned, the headlamp, the parking lamp (not sure what that even is), the speedometer lamp, and the horn switch, all of which I assume are wired through the headlight bucket. I suppose I should trace the wiring for each of those lamps and determine what's missing through the process of elimination. Does this sound about right?


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PostPosted: Mon Aug 20, 2018 3:14 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3416
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
B/W is always ground.

The speedo & tach have a lightbulb that is on when the headlight is on. Gr wire is power from the headlight switch. B/W wire is ground.

Neutral light: O wire is power from the ignition switch. Bl wire goes to the transmission neutral switch.

High beam light: Y wire is high beam power from the dimmer switch. B/W wire is ground.

Turn signal indicator: B wire is power for the left turn signal from the turn signal switch. Lg wire is power for the right turn signal from the turn signal switch.

If you are using LED turn signals, then you have to wire up the turn signal indicator differently.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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PostPosted: Mon Aug 20, 2018 5:23 pm 
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Around the block

Joined: Fri Nov 30, 2012 8:27 am
Posts: 89
Country: USA
Bikes owned: GT550
It's worse than I recalled. See attached pics. On the left side of the pics, you can see the problems. There are several grey wired that are spliced together and lead to one grey wire with a bullet connector and no mate. There are several black and white wires spliced together to a single BW wire with a bullet connector and no mate. Then there is a brown wire and a black wire with bullet connectors and no mates.


Attachments:
File comment: Single brown and black wires
bucket wiring 2.jpg
bucket wiring 2.jpg [ 126.78 KiB | Viewed 1415 times ]
File comment: Grey and BW wires
bucket wiring 1.jpg
bucket wiring 1.jpg [ 216.18 KiB | Viewed 1415 times ]
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PostPosted: Mon Aug 20, 2018 7:27 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3416
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
The B/W wires are grounds. Its ok if they are all spliced together as long at it is a good reliable connection.

The brown wire is for a parking lamp. Stock headlights in the US are sealed beams that do not have a parking lamp. So that wire is unused.

The unused gray & B/W wires most likely are for either the tach or speedo lamp.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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PostPosted: Mon Aug 20, 2018 7:35 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3416
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
What is going on under that gray electrical tape?
Is that a twist-on connector near the top of the first pic? Twist-on connecters are fine for your house but not vehicle.
Wires that are just twisted together is unacceptable.

Modern crimp-on connecters are good.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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 Profile  
 
PostPosted: Tue Aug 21, 2018 2:30 am 
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Around the block

Joined: Fri Nov 30, 2012 8:27 am
Posts: 89
Country: USA
Bikes owned: GT550
jabcb wrote:
The B/W wires are grounds. Its ok if they are all spliced together as long at it is a good reliable connection.

The brown wire is for a parking lamp. Stock headlights in the US are sealed beams that do not have a parking lamp. So that wire is unused.

The unused gray & B/W wires most likely are for either the tach or speedo lamp.


This is very helpful. Thank you so much. I put the old style speedo and tach into the ‘75 housing. Am I right that the grey and B/W wires for the tach and speedo lamps then simply can’t be used until I install ‘75 speedo and tach? In other words, does the wiring for the ‘75 speedo and tach come directly from each clock?

If so, that just leaves one mystery black wire with a bullet connector.


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PostPosted: Tue Aug 21, 2018 2:32 am 
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Around the block

Joined: Fri Nov 30, 2012 8:27 am
Posts: 89
Country: USA
Bikes owned: GT550
jabcb wrote:
What is going on under that gray electrical tape?
Is that a twist-on connector near the top of the first pic? Twist-on connecters are fine for your house but not vehicle.
Wires that are just twisted together is unacceptable.

Modern crimp-on connecters are good.



I know. It’s a mess. Thus, the topic title. I’ve got to clean all of that up. For the wires that are twisted together, what’s the proper way to do that?


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PostPosted: Tue Aug 21, 2018 4:02 am 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3416
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
Modern crimp-on connectors that are available at your local auto parts store work just fine.
If you want to return it to the original setup, you can get the connectors at: http://www.vintageconnections.com

A lot of the vintage bikes we are now riding were parked years ago because of issues that the owner just didn’t want to, or couldn’t, deal with. Some of us have seen worse electrical gremlins than what you have. One of my bikes is a barn find that had a strand of throttle cable wire broken off — it made the bike impossible to tune up correctly. By sorting through the gremlins now, we can end up with nice reliable vintage bikes.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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PostPosted: Tue Aug 21, 2018 7:18 am 
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Around the block

Joined: Fri Nov 30, 2012 8:27 am
Posts: 89
Country: USA
Bikes owned: GT550
Thanks. The PO changed the gang connector to bullet connectors to accommodate the old style gauge. I purchased the correct connectors from vintageconnections.com. I crimped the wires and inserted them into a 6-gang male connector, but there were only 5 wires. The missing wire is a B/W wire and I’m not sure which one it should be. Does it matter since they’re all grounds?

As for crimping three wires together, what kind of crimp?

I’d love to put it back to original, but I don’t know what all has been changed. Any info on the original setup?


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PostPosted: Tue Aug 21, 2018 4:11 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3416
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
Do a little planning. The B/W wires will have different lengths. Pick the B/W wire arrangement that works the best based on wire lengths.

Its wise to do some testing as you go. Make sure what you are expecting to work actually works.

Suzuki used some bullet connectors that connect 3 wires together. Vintage Connections sells them but they seem a little flimsy. A modern crimp-on butt connector with two wires on one side & one on the other is good but its permanent.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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 Profile  
 
PostPosted: Tue Aug 21, 2018 8:53 pm 
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Around the block

Joined: Fri Nov 30, 2012 8:27 am
Posts: 89
Country: USA
Bikes owned: GT550
Great! Thanks so much for the help.


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