76 GT550 Blown Fuse?

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Syd
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Joined: Tue Aug 16, 2011 11:25 pm

76 GT550 Blown Fuse?

Post by Syd »

Hello, I would appreciate some guidance on trying to locate the reason for my GT550 blowing fuses following a frame up restoration. Everything has been running fine with no electrical issues or problems. I took the bike for a short ride today and when I went to ride back, the fuse went after I turned the key on (the lights were not turned on at the time). I replaced the fuse with the spare fuse and as soon as the key was turned, the fuse had blown again. I got the bike back to my place and checked my Suzuki GT550 service manual which is a photo copy version off eBay and there really does not seem to be which info on electrical trouble shooting or a check list to follow. Has anyone had any experience with this type of problem with a GT550 as any tips would be much appreciated.
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Alan H
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Location: Wombwell, Republic of South Yorkshire

Re: 76 GT550 Blown Fuse?

Post by Alan H »

Hi Syd,
Hopefully just a trapped wire, but we'll find it!
What model 550 have you got? They are all similar, but there are a few differences.
First of all you need 'a few' 20 amp fuses, then we can begin!!
Side panel off as we need to know if it blows fast or slow. Then, ignition and kill switch off, lights off. Fit new fuse.
Ignition on, does the fuse blow or start to get warm?
Kill switch on does the fuse blow or get warm?
If ok up to there, will the bike start on electric or kick?
I would guess by now that a fuse might have failed, so we (you really), will have to lift the tank off to see the coils and also remove the headlight to access wiring inside.
Check for any flattened wiring inside the headlamp, where the tank locates near the steering head and coils, and also under the left sidepanel are near the 3 plugs under the regulator (area.)
No issues? Pull the 3 plugs from alternator, reg and rectifier and switch on ignition, then after a few seconds, kill switch. All ok? If ok, then you've unplugged the fault, if not it's somewhere else, but we are narrowing it down.
Leave both switches on and replace alternator plug, then rectifier plug, lastly regulator plug. Wait a few seconds after each plug in to see if the fuse fails.what we are doing here is to narrow down where the fault is.
Can you use a multimeter and understand what the readings mean?
Next exciting installment when you re-post with some results!!
Proof that four strokes are over complicated
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Alan H
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Location: Wombwell, Republic of South Yorkshire

Re: 76 GT550 Blown Fuse?

Post by Alan H »

Hmmm. No replies suggest it's sorted, or a suicide. :o
Proof that four strokes are over complicated
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Syd
Posts: 311
Joined: Tue Aug 16, 2011 11:25 pm

Re: 76 GT550 Blown Fuse?

Post by Syd »

Hello Alan - I did send you a PM on the 28 June 2020 with answers to your questions which I have shown below

All the lights and indicators work fine when the kill switch is in the off position. When turned onto the run position, the neutral light dims and the indicators light up but will not flash. I then unplugged the voltage regulator plug on the panel and there was no change and then plugged the rectifier plug - same result and then the alternator plug - same result. With all 3 plugs pulled out, I have the same symptom ie: normal lights and indicators flashing when the kill switch is off and dim neutral and no flashing indicators when the kill switch is on.

I checked out all of the connections inside the headlight and also checked out the kill switch operation using a meter at the plug connection wiring in the headlight - all fine. I then disconnected the flasher relay and the lights and neutral light are fine with the kill switch off and/or on.

Coils - I had fitted new copy coils from Legend Motorcycle eBay site in the UK - see below:

https://www.ebay.co.uk/itm/NEW-Suzuki-T ... 1939087767

I did the following checks with the coils - I removed the wires from the LH coil and the lights and flashers are all good with the kill switch off and the neutral is dim with no flashing when the kill switch is on run. Put the wires back onto the LH coil and removed the wires from the centre coil and again, the lights and flashers are all fine with the kill switch in the off position and the neutral dim and indicators not flashing when in the run position. Refitted the wires to the centre and then removed the wires from the RH coil which showed again the lights and indicators are all good with the kill switch off, however in the run position, the neutral was a little brighter and also the indicators flashed a couple of times then stopped. I then removed all of the wires from all of the coils and the lights, neutral lamp and flashers all work with the kill switch in either the on and/or off position.

I then disconnected the wires on each coil one by one and measured the resistance across each coil with the coils leads pulled off the spark plugs. The readings were LH coil = 2.9 ohms, Centre coil = 2.3 Ohms and RH coil = 1.3 ohms. I then checked and did the same on the original old Suzuki coils which I still have and got the following readings. LH coil = 4.0 ohms, Centre coil = 3.4 ohms and RH coil = 3.4 ohms which I thought was interesting.

So, thinking the RH coil could be the problem, I refitted the original RH Suzuki coil, however this did not solve the problem so I changed the coil back to the copy coil. The battery is a new gel battery and the starter button motor kicks over fine when pushed, however in doing all of these checks, I have had to replaced two more fuses and to me, the fuse seems to be slowly blowing. I have the petrol tank off so I have not had the engine running again while doing these checks and I have double checked all of the earth leads and contact points and they all seem 100% as I did everything carefully with my ground up restoration over the last few years.

In the meantime, I ended up removing the copy coils and refitting the original coils after doing some repairs to some of the coil wires and now everything seems to be going ok so hopefully this may have fixed the problem for good.
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Alan H
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Location: Wombwell, Republic of South Yorkshire

Re: 76 GT550 Blown Fuse?

Post by Alan H »

Syd wrote: Sun Aug 29, 2021 11:25 pm Hello Alan - I did send you a PM on the 28 June 2020 with answers to your questions which I have shown below

All the lights and indicators work fine when the kill switch is in the off position. When turned onto the run position, the neutral light dims and the indicators light up but will not flash. I then unplugged the voltage regulator plug on the panel and there was no change and then plugged the rectifier plug - same result and then the alternator plug - same result. With all 3 plugs pulled out, I have the same symptom ie: normal lights and indicators flashing when the kill switch is off and dim neutral and no flashing indicators when the kill switch is on.

I checked out all of the connections inside the headlight and also checked out the kill switch operation using a meter at the plug connection wiring in the headlight - all fine. I then disconnected the flasher relay and the lights and neutral light are fine with the kill switch off and/or on.
Hi Syd, I don't remember getting a pm about that (but I have slept since then, and the memory only works in fits & starts nowadays!)
Did you change the flasher relay and is all ok now? The neutral light will dim slightly when the kill switch goes on, as the power also goes to the coils plus regulator and alternator rotor at the same time. The power goes to the indicator relay (plus lights etc) as soon as the ignition is switched on, so the favourite will be a bad earth 'somewhere' or even a bad connection.
I usually 'daisy chain' a negative from battery to solenoid, indicator relay, rectifier mount and regulator to help with earth issues in that area. Trouble with 40+ year old bikes is they're full of 40+ year old wiring that might have been 'adjusted' by previous owners..... :roll:
You can pull every connector apart (separately so they can't be re-mantled incorrectly, ( :shock: ) , and put them back together and you might get lucky without actually finding the culprit, or notice a bad/corroded joint. At least you're not scared of wires and a tester.
Proof that four strokes are over complicated
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Syd
Posts: 311
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Re: 76 GT550 Blown Fuse?

Post by Syd »

Hi Alan - Yep, know what you mean about the memory..

I did not replace the flasher relay, however I did go through every wiring connector and also the earthing side of things so I think this is all fine. I'll see how things go from here - cheers
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