1976 gt550 short/fuse blowing

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rderrick121
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Joined: Thu Nov 29, 2018 10:31 pm

1976 gt550 short/fuse blowing

Post by rderrick121 »

Hello, I just got my gt550 out of the corner and wanted to get it going for the season. The fuse blew quickly. I have isolated the issue to be something wrong with the run/off switch you use your right thumb on, the switch looks to be pretty clean and I touched it up further. I replaced the fuse and when you set the switch to run you notice the lights dim heavily and it will blow again if left on for more than 2-3 seconds. It only takes about a second for the fuse to get hot. If the switch is left in the off position and key on it seems to be fine. The issue only happens with the key on and you switch it to run. If you disconnect the switch behind the headlamp it does not short. There is some weird burn in the connectors but it doesn’t seem like this would be the cause. Looking in the connectors it doesn’t seem burnt, I see the wires are a little bare in the pictures below and that is not the problem as I made sure they were not shorting. I will wrap them before putting it back together.. Anybody know anything else I can check? I cannot see more of the wire after it goes into the harness. All other wires I can see look to be ok. There are 2 plugs not connected pictured below. Additionally can you advise on what all of these electrical components are next to where your left leg is? Thank you, Richie.
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slosher
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Re: 1976 gt550 short/fuse blowing

Post by slosher »

Hi Richie parts down by your left leg top left solenoid,top right voltage regulator,btm left flasher unit and btm right is your rectifier and of course your fuse holder which you have already found by the sound it :) Start with bad earths with the wiring problem
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rderrick121
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Re: 1976 gt550 short/fuse blowing

Post by rderrick121 »

Hi slosher, when you say bad earths do you mean the main ground? If so that looks good, runs from the battery to the right side of the engine case. Thanks.
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slosher
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Re: 1976 gt550 short/fuse blowing

Post by slosher »

rderrick121 wrote: Tue Apr 06, 2021 9:28 pm Hi slosher, when you say bad earths do you mean the main ground? If so that looks good, runs from the battery to the right side of the engine case. Thanks.
Hi Richie it could be any earths or bare wires touching frame,headlamp ears,handle bars etc,i had a GT250 that would blow a fuse sometimes or completely drain the battery :x took me months to find the problem,it was down to the front left indicator wire touching the inside of the neck on the stem,on my 550 the block connector for the gear position indicator had been fitted incorrectly :oops: that kept blowing the main fuse when i changed into 3rd gear honestly it could be any number of things, don't forget these bikes are nearing 50yrs old mate
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Alan H
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Re: 1976 gt550 short/fuse blowing

Post by Alan H »

When the 'kill' switch is turned on, as well as putting power to the coils, it also powers up the regulator -- which in turn puts power to the alternator rotor. There are other bits too, but we have to start somewhere.
Make sure the brake light bulb isn't knackered as this can cause issues too.
Pull the plug from the regulator as a start to see if that makes a difference - and make sure the light switch is 'off'.
I take it that the fuse is rated 20a as recommended?
Proof that four strokes are over complicated
rderrick121
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Re: 1976 gt550 short/fuse blowing

Post by rderrick121 »

Hi Alan, tomorrow I’ll unplug the voltage regulator and see if it quits. The fuse is 20a Thanks.
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slosher
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Re: 1976 gt550 short/fuse blowing

Post by slosher »

Richie the voltage regulator may only need adjustment if you open the box up two tiny screws you will either have a Denso unit or Kokusan the Denso type you have to bend the blades Kokusan you can adjust with a tiny screw they look similar to a small set of points.Mine were fused together ;) this unit allows the correct voltage back to your battery if it's not doing it's job then high voltage will tend go where ever it wants to ;)
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rderrick121
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Re: 1976 gt550 short/fuse blowing

Post by rderrick121 »

Hi Alan, I unplugged the voltage regulator and the fuse does not blow. It still does load down a bit when moving the kill switch to run — the neutral light dims but not nearly as much as it was. Slosher, I played around a bit with the contact a bit in the regulator. I found that when the regulator touches the post near me it’s causing the heavy draw. When I added the paper towel breaking the contact pictured below the bike operated as it should, I even fired it up for a few seconds. Man do these thing smoke after sitting for a winter... I looked at the adjustment screw and there’s no way to move the thing in the the regulator so it doesn’t touch that outside post. Any insight? Which post should it touch?
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slosher
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Re: 1976 gt550 short/fuse blowing

Post by slosher »

Richie
I think with the unit you have, slacken the nut on the screw you then need to start the motor up try and hold revs around 3000 rpm (you need about six pairs of hands at this point :lol: ) then drop a multi meter over the battery terminals then adjust the screw in towards the blade until you see a reading of about 14.1 volts on the meter then lock the nut up, this being enough to keep the system charged and not frazzle either the battery or any wires.

PS The point on the the screw shouldn't touch the post or the blade there will be a tiny gap between the blade and the point of the screw if that makes any sense mate

Cheers Dave
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rderrick121
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Re: 1976 gt550 short/fuse blowing

Post by rderrick121 »

Hello Dave,

I tried adjusting the regulator and ended up with still no charge. The voltage on the battery with the key off is about 12.2 and with it on and running about 11.7. Also my headlight does not work now... man I love this old bike but it’s testing my patience lol.

Thank you,

Richie
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