Hi All,
I wonder if anyone could assist me with finding the cause of my bike keep blowing the fuse when running.
I have narrowed it down to the rear brake light.
When the ignition is on without the engine running the lights and brake light all work as they should.
However, with the engine running I apply the rear brake and the engine cuts out due to the blown fuse.
Is this likely to be the switch shorting out? Even though it works fine without the engine running?
What tests could I carry out to pin point the fault?
I can't find any loose or damaged wires.
Thanks in advance.
Wilf
Hi Wilf,
When it blows are all the lights on or just the rear brake light? What fuse are you using? It could be shorting when running as a wire makes contact due to the vibration so stick with investigating the rear brake switch and wiring.
Dave.
It's hard to see why the engine running should cause this fault. You say it happens when you apply the rear brake but does it happen if you switch on the headlights instead?
If it only happens with the brake light, I would disconnect the brake light circuit which gets its power via the white wire from one of the coils - there may be a bullet connector on the white wire close to the brake light switch. With the white wire disconnected, you can then test the brake light circuit does not cause a short by measuring the resistance between the end of the white wire and an earth point on the bike with the brake is applied.
However, if something is shorting to blow the fuse, it's hard to see why running the engine should make a difference. Might be worth measuring the battery voltage with the engine running to check there isn't something unusual going on with the charging circuit.
Thank you both for the suggestions.
I haven't tried it with the lights on and the engine running.
I will try that tonight.
I have a 35A glass fuse fitted,
I have also tried disconnecting the Zener diode but this made no difference.
Checked battery voltage when running and seems to be normal.
The bike is running a Pazon electronic ignition system if that makes any difference?
Not sure if it's relevant or just coincidence but last week the ammeter failed, which I though was the cause of me breaking down. Now I have that sorted I have the issue with cutting out / blowing fuse when rear brake applied.
I will try disconnecting the white wire from the brake switch and see if there is a short to ground.
Thanks,
Wilf
Normally, as said, a separate white wire from the ignition switch provides power to the coils with a separate white wire then going to the rear brake circuit. Just Looking at the Pazon ignition wiring diagram, it looks as though the original white wire to the coils is replaced by a feed from the new ignition module. If this is what you've got, it begs the question of where your rear brake light circuit now gets its power from now. It may well be spliced into the original white wire from the ignition switch but it would be well to check how the wiring has been modified.
The white wire coming out of the loom near the coils now feeds the Pazon ignition module. And then a +ve and -ve come out of the module to go to the coils.
A separate brown and white wire come out of the loom that connect to the stop switch.
I have just started the bike and turned the lights on - with no issues.
If I briefly blip the back brake the ammeter shoots over to the positive side and the engine revs dip down. If I were to keep the brake pressed I'm sure the engine would stall.
With the rear stop / tail light bulb removed it's still the same.
This must be causing the fuse to blow with the excessive current.
Any ideas as to why the increase in current from pushing the rear brake?
Thanks,
Wilf
I assume there is an earth connection on the same side of the +ve wire connection to the coil as per the Pazon wiring diagram? At face value, it looks as though there may be an earthing problem and this may be causing the output of the Pazon ignition module to effectively find its way into the charging circuit, causing what you see on the ammeter and resulting in too large a current flowing into the battery and blowing the fuse!
Apart from checking the coil earth connection is in place, I would look to see where the brown/white wire to the rear brake circuit comes from. In the normal wiring harness, the only brown/white wires connect between the ammeter and headlight switches. I assume that if you can disconnect the brake switch from the brown/white wire, the problem will not occur?
What I would do is work out where the brown/white wire is connected to at teh other end.
Sorry I may have not worded it correctly. It's not a brown / white wire to the switch it's one brown and one white. So they are the two wires that connect to the brake light switch.
I have checked that white wire to ground and it's showing continuous.
However, if I disconnect the oil pressure switch there is no connection to ground. This is without the engine running, but with ignition on.
It shouldn't need two wires going to the brake light circuit - it just needs one 12 V supply! I would check where they both go?
I'm not sure I fully understand the comment about the oil pressure switch. Are you saying that the +ve coil coil connection to ground disappears if you disconnect the oil pressure switch? If this is the case, this would suggest that the engine is not properly grounded to the bike's frame and might be where the problems lie?
:) :) :) :)
My Answer, at least to isolating the problem would be to jury rig a feed to offending light direct from the battery (or similar) and see what happens. Often these wriggly amp probs are a mindless ache to sort. If that cures it you can then choose whether or not to leave it so rigged or pursue the problem. If it doesn't cure it ---no loss except time.
Mike 8) 8) 8) 8)
Thanks for the suggestions.
I have a feeling that it could be something to do with the rear light shorting out somewhere.
I will disconnect it and work through the wires / connections to that.
The two wires on the brake light switch are a white 12v feed and then the brown going to the rear light.
It is this white wire that is continuous to ground until the oil pressure switch is disconnected.
I guess that's correct though for the oil pressure light to illuminate when engine not running.
Regards,
Wilf
The white wire to the brake switch should be connected to 12 V with the ignition on with a branch off it at the ignition/lighting switch to the oil pressure warning bulb and then to the oil pressure switch. With no oil pressure and the ignition on, the oil pressure switch contacts will be closed and provide a path to ground to illuminate the warning light.
With the rear brake off, the white wire to it should have a resistance of about 72 Ohms to ground with the ignition off. This will just be the resistance of the 2W oil pressure warning light connected to ground via the pressure switch.
I would definitely disconnect the white wire to the brake switch and check it gives 12 V with the ignition on. I think you then need to work out why it appears to be shorted to ground with the ignition off - the only reasons I can see for this are if the oil pressure warning light is shorted or your Ohm meter is giving a false resistance?
I think I may have found the issue!
After tracing back the wires to the rear light I have found one of the wires to have chafed on the rear mud guard clips.
I'm fairly certain that this is the issue, causing the fuse to blow when the rear brake is applied.
I will repair this section tomorrow and give it another try.
Thanks for the help and suggestions.
Fingers crossed I can get out on the road again tomorrow with no issues.
Regards,
Wilf
An easy way to find wires that have shorted for what ever reason, is use a multi metre set to omhs ground the black wire of the multi metre to the battery ground and touch the other end to the live wire that is causing an issue. If you get a 0.1 or up the range to 0.6 then you know that wire is connecting with ground. Saves a whole lot of time.
I've only just read this whole thread and right from your first posting I suspected a bare wire somewhere in the brake light circuit.
I had a similar problem many years ago on my then current Thunderbolt. I rewired it with a new loom and the oil pressure lamp assembly, an idiot light with one lead in and a bullet captured in the metal lamp casing i.e earth was wired the wrong way round (in the loom). the casing was perilously close to the headlamp reflector and with the vibration, would touch and blow the fuse. Took me longer to work it out than fix.
At least I have found the issue now. I found that one of the two wires going to the rear light had rubbed on one of the metal clips in the mudguard.
I have now replaced the wire and put heat shrink over the top where it passes through the clips.
All appears to be working fine now.
I think what threw me off from the start was the fact that the rear light and brake light worked fine without the engine running.
Maybe the exposed wire was only a small amount to start with.
Electrics isn't my strong point, but got there in the end with the help of this forum.
Thanks for all of the replies and suggestions.
Regards,
Wilf