Electrical Meltdown

Willz900

Willz900

Junior member
Location
Eastbourne. UK
Hi Guy's,
              I have not had the bike a week yet and I was about to take it out and it blew the 25 amp fuse, which I replaced and all seemed fine and when out for a short blast, but when I got home found that the rear light would not go out without removing said fuse.

After further investigation, I found the connecting plug and wires in the head light going to the ignition switch had overheated.

Any idea's what could have caused this, ? I thought that maybe the wires that go to the rear under the seat and along the frame might be damaged as the seat rubber was pressing down on them, but they look o.k.
 
The ignition switch carries all the electrical load for the bike, so any poor/loose connection there will rapidly overheat.  You need to cut out and replace the overheated connector & wiring. 

However, that doesn't necessarily explain the 25 amp fuse blowing.  I suspect you may have a short somewhere .... insulation rubbed through so that a wire can intermittently go to earth.  That makes it a challenge to fault find....but do the obvious stuff first.  Look for worn insulation - around the steering head is a good place to start - or bodged wiring.  I'd also carefully recheck that wiring under the seat.
 
You have probably found why the previous owner sold it.
The bike is over 30 years old and has likely been through multiple owners so it's no surprise the wiring is dodgy.
No easy fix. Start at one end and confirm ALL connector blocks, signs of damage or overheating.
But once it's done properly it will he a joy for a long time.
 
My 81 1200 had blown that fuse and melted all the wires up to the handlebar switch before I bought it. By trial and error I traced it to a short in the headlamp bucket. It was so bad I'm surprised the bike didn't go up in flames.
 
I have a friend that was an auto electrician, who is coming over tomorrow to have a look.

I'm not sure that the p.o knew about this, as it was alright to begin with and the wiring doesn't look hacked about, just bad luck. ::)

It could have been worse, but that's what I always say. :D
 
Willz900 said:
I have a friend that was an auto electrician, who is coming over tomorrow to have a look.

I'm not sure that the p.o knew about this, as it was alright to begin with and the wiring doesn't look hacked about, just bad luck. ::)

It could have been worse, but that's what I always say. :D
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If your friend is taking his job for serious, his proposed fix should sound like 'throw the entire mess of 40yr old corroded cables and connectors out and renew it'. Even more so as you already have been close to a burning wiring loom, as it seems.
What bike? If a 3C or 3CL, I can provide an updated wiring diagram which resolves most of the shortcomings  of the original wiring, e.g. avoids sending the complete power through the ignition switch and other upgrades.

Regards,
Stefan
 
Seems I was lucky and it was just the connector from the ignition switch that had to be replaced, all the rest of the wiring seems sound.

Hi Stefan, he is a retired auto electrician and doesn't know a lot about bikes, but if you have a diagram that might help in avoiding this kind of thing again, I would be grateful for it.

It's a '81 3CL Jota.  :D

                                      Thanks for all your replies. Will.
 
mauricejota7604 said:
Hey Will if you still have the original ND ignition switch peel the rubber from the back and check that you also dont have a soldered wire coming off (very common)
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Or the soldered joints have become corroded and or one of the wires has got corrosion in it thus causing a high resistance which end result is melted terminals. Fairly easy to unsolder the wires and solder a new set into place. Remember that when soldering to have a nice clean joint and best to use a flux pen and if you can find some old lead type solder even better.
 
If your using the green book wiring diagrams take care you use the diagram for the right year, they changed the wire colour for different years. I replaced the damaged wire only to watch it start to melt again. I used the wrong diagram and melted some insulation repairing an earlier bit of damage. Seems its a mistake  also done before I owned the bike. So this must be a common error over the years.
 
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