Hot battery terminal

Hi - brought my 850 Commando back to life (at last!) after it had a few electrical gremlins back in 2004 (backfiring and then loss of spark altogether). Thought it was Boyer related so replaced a few items that a friend had surplus (new coils, Boyer 'box') and fixed kill switch (which had broken). Replaced all oils, cleaned out carb, got a newish battery from same friend and kicked away. The bike started in about five kicks and ran faultlessly, couldn't be happier.

A week later, go out in the garage to start the bike again to go for a quick ride and no electrics - no lights, horn, blinkers etc , all that worked was the Parking position on the ignition switch. Checked battery and still giving out 12.3V. While testing battery performance, I also noticed that while the ignition switch was on, the negative battery terminal got very hot to the touch. Thought it may have been bad contacts or suchlike in the ignition switch so bought a new switch and installed - no change.

So I assume I have a short somewhere, but, can anyone hazard a guess why that could happen? After all, the bike had just been sitting there for a week, doing nothing, after running perfectly. Any idea where to start looking? I'm an electrical dolt so tracing the whole wiring loom probably isn't a suggestion I can carry out!

Many thanks

Ken

Wowski !, Your battery terminal should never get hot for any reason so this tells me it's time to talk about fuses.Modern fuses are rated differently than genuine article and you could easily be running a fuse that allows too much current through it before it blows. This fuse should be close to the battery so open it up, clean, inspect it's type and load numbers. I use a 17 A. I believe at last check, with another Inline to protect the Boyer circuit of lower number.This winter will see a move to 4 fuses to protect circuits and help trace the source of any difficultys as you can then locate which circuit is giving you shorts and grief. Good luck plus never forget the pos. ground thing.Also the Boyer wires into the points cavity can fail there from vibration so check there,perhaps shorting there,report back, Peter.

vmxken said:

I also noticed that while the ignition switch was on, the negative battery terminal got very hot to the touch.
Ken

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Heat = resistance with voltage or current. I would suspect your battery terminal is suspect. Make sure everything is tight, not corroded. It doesn't take much resistance (heat with current) to make the voltage drop so much your EI is not working. If you have a volt meter, measure the voltage at the coils compared to the battery terminals, ign on. If it's less by more than 1/10's somethings wrong and you need to find the culprit in between.

Good luck,
Dave
69S

vmxken said:

the negative battery terminal got very hot to the touch

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I agree with DogT. If the entire wire was hot leading to the negative post, then I'd worry about a fuse problem, but if the heat was confined to the post/connection, you can almost bet it is too much resistance in that connection (unless an unlikely internal battery problem - which in actuality would still be a problem with that connection). Also, not a big deal, but bear in mind that 12.3 volts in a 12 volt battery represents only about a 70% state of charge. By the time you get down to 12.0, you're at approx. 50%. You might want to charge the battery and load test it and also check the charging rate; just to cover all the bases for the future.

vmxken said:

Checked battery and still giving out 12.3V.

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To test the battery you will nead to measure the voltage under load. It sounds like you have a digital multimeter already so if you have a couple of test leads with alligator clips you could put a lamp across the terminals and measure the voltage. If it is still 12.3 V that would suggest the battery is fine.

If you have a battery charger with an ammeter you could also try connecting the charger and turning on the key. The ammeter should go full scale if there is a short somewhere.

A good multimeter can also help to find a short becauses there are millivolts of difference along a wire because it has some small resistance.

Check all the wires you can see to see if the insulation has rubbed off where the wire touches metal. That can be fixed with some electrical tape or heat shrink tubing.

Beyond that it is best to find someone that can read the schematic diagram and use that to disconnect and test each sub circuit. If it is a dead short it should not be too hard to find.