Electrical tinkering for beginners

I had the motherboard replaced on my alarm last week as it was playing up. Didn’t ride the bike again until heading out for work on Monday. Bike wouldn’t start - not enough juice in the battery to turn the starter. I had a spare battery in the shed so stuck it on charge on the Optimate (indicated “good”) then put it on the bike last night. Bike started fine. This morning - no start!

I’ll be speaking to the alarm people to see if they know whether anything they did when repairing the alarm might be causing the drain. Assuming they deny it’s anything to do with them (!), how can I trace the fault myself? I have a multimeter and tools but no technical savvy! Bike is booked into the dealer but they can’t fit me in until next Weds. I really don’t want to miss out on a long biking weekend.

Cheers for any advice.

This should be useful -


Thanks, I think (scratches head)!


I will try and simplify it.

Disconnect the battery negative lead and connect it to the red lead of your multimeter. Connect the black lead of the multimeter to the negative battery terminal.

Set the multimeter to the 2 Amp range.

With everything turned off check for any reading. You should only have the alarm draining about 0.1 amps (ish). If you have more current than this try pulling the fuse on the alarm and see if the reading drops to zero or 0.1 amps or less.

Essentially pull fuses until the meter drops to zero or close to zero. There’s the problem, you have found the circuit that is causing the drain.

Nice one. I’ll give it a go this evening

The point of the article I posted is that there are loads of things that are meant to draw current on a modern vehicle which makes the process much more complicated than it used to be. Whilst drawing fuses will show the current that circuit is drawing, that might not help much unless you know what current it is meant to draw. As a first step see what happens when the alarm fuse is pulled as the alarm would seem to be the obvious culprit and compare that with the current it should draw. BTW I don;t know for bikes, but in many models of car the clock is often the cause for massive current drain. They are meant to draw a few milliamps but can go faulty and draw a lot more. Shorting in the alternator is also often the cause, but after market items like alarms are top of the list.

Thanks Spannerman and Giuliano - forgive my numpty response to your post.

Didn’t get anything from the multimeter. Re-swapped the battery in case it was a dud. Bike started this morning (surprise) but sounded a bit sluggish. Will see if it starts tomorrow…