Electrical Fault

Hi Philip

When you connect a battery to a bike's electrical system you must always connect positive to positive and negative to negative. To do it the way you described will cause damage and you would be lucky to get away with a blown fuse.  The Dominator, which I am  more familiar with, has a positive earth system; the battery positive terminal must be connected to the frame.  If the Commando has a negative earth system then the negative of the battery must be connected to the frame.  

When you use an ohmmeter to measure resistance you should also take a resistance reading with the leads of the meter  reversed as electronic components, such as diodes, offer a different amount of resistance according to the polarity of the applied meter voltage. So, you may have a resistance of 1.5 ohms with the meter leads connected one way around, reverse the leads and it might be 150 ohms, depending what is in the circuit the leads are connected to.

The failed circuits will probably be the one with electronic component, such as the the rectifier and voltage regulator, also, if you have electronic ignition, that might be blown.

Hi Philip, 

As above, I dread to think what damage has been caused, but your original problem sounded like you had ONE wire wrongly connected. On the mk3 its black to black - and red to red+. You may have mistaken one of the smaller leads. The RED is EARTH and is usually the terminal on the outside. Try connecting like this and see what happens. 

... can be quite confusing especially as virtually all modern vehicles are the other way round. I'm lucky in that my ES2 was made in the "negative earth window" but even if it hadn't been I may have changed it as my brain cells slowly deteriorate.......

That was a close one Philip ! I am paranoid about my cables coz I have four on each battery terminal. I have a large red collar on the earth cable which is otherwise black,  and zip tie the + &  -- wires together. Good result mate.

There are several confusion points here. As has been said the POSITIVE TERMINAL OF THE BATTERY is RED and connects to the POSITIVE cable on the bike. Dommies and Commandos came out of the factory as positive earth. The order of connection is NOT normally important except in this situation-which refers to ALL vehicles.

When disconnecting a battery, disconnect the EARTH first.(Then a slipped spanner or screwdriver on the Live does NOT result in a large bang!)

When reconnecting  a battery, reconnect the LIVE first. (Then a slipped spanner does not result in a melted spanner) 

If the terminals of the battery have more than one wire and/or they differ from RED and BROWN/BLUE, there will eventually be confusion and expensive noises. Be warned. One wire on each terminal.

Measuring resistance in the above situation is not worthwhile. Rectifiers and bulbs and LEDs give strange results unless you know what you are doing. With this level of electrical understanding please stick to measuring voltage. Current and Ohms testing needs to be understood fully to serious avoid confusion.

Some brake switches  look correct but work the opposite way  (Triumph type) ,  Some less than scrupilous  Norton  sales outlets were selling them  when the correct type were scarce.  They suggested that you could fit them upside down  .  I did manage to convert  one type to the other ,but it was not simple. 

Hi,

Further to Roberts answer, the standard switch should be 'normally on', i.e.  when the plunger is pressed the switch should go open circuit. The Triumph ones are 'normally open', I.e pushed in to complete the circuit. 

I had one of these '31383' type switches melt internally, leaving the brake light permanently on at about 1/4intensity, making me think the tail light was on all the time, whereas it was just the brake light lit. When my switch was operated, the melted part of the switch was bypassed and the lamp was at full brightness. 

Also, check the earth's are good - add an additional earth wire if necessary - as it is sometimes possible for one light to complete its circuit via another. (I'm sure that you have seen older cars  that have had the tail lamps dimming in sympathy when the indicators were on).

Good luck, 

George. 

These switches collect grit and water ,wear out and  go green inside, Someone must have come up with an effective cover ,  let us into the secret !.  

Especially as this is an Electrical issue not a Commando issue.

But the culprit here is mostly the rusty mudguard....doesn't make a good earth. Run a fresh earth wire and/or rewire the whole bike.