Brake light robbing electrical power

Hi guy's,
Is it normal for the headlight to dim and blinkers to slow their flashing rate when the front brake activates the brake light???
It seems like the brake light is draining the electrical power, just enough to make this annoying.The rear brake globe is (12V /21W 5amps)
I currently have this problem on my MK II 850 Commando. It is more apparent with Hi beam on.

Brewer.

Brewer said:

Hi guy's,
Is it normal for the headlight to dim and blinkers to slow their flashing rate when the front brake activates the brake light???
It seems like the brake light is draining the electrical power, just enough to make this annoying.The rear brake globe is (12V /21W 5amps)
I currently have this problem on my MK II 850 Commando. It is more apparent with Hi beam on.

Brewer.

Click to expand...

Hi this can be 'normal' depending how good the alternator/regulatot rectifier set up is on your bike and if the battery is in very good condition. I have a 74 Commando and fitted a high output alternator and a modern regulator/rectifier. If you have a voltmeter check the voltage across the battery and see how much it drops with main beam on and using the brake with and without indicators. Also check the voltage across the battery again with no lights on and with the engine revving to 2500 rpm Post the results .(It is more aparent at high beam because the headlamp on high beam is a higher wattage than on dip (takes mor power))

Brewer said:

The rear brake globe is (12V /21W 5amps)

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5 Amps, that would be the current drawn by a 60W (60W/12V = 5A) bulb?

The standard bulb/globe is a double filament 12V 21/5W (12V - 21W brake, 5W tail).

Hi L.A.B,
Yes! the globe is a 12V 21/5W, I made a typo in saying it was 12V 21/5 amps.

Is this tailight electrical drain a common accurance with Commandos?

Brewer.

Is this tailight electrical drain a common accurance with Commandos?

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Based on the voltage measurements I took/noted in the "Lighting Efficiency" thread here, I'd say not. Have you considered a frayed wire/incipient frame short somewhere in the brakelight circuit? (Start with the footswitch and work back.)

Brewer said:

Hi L.A.B,
Yes! the globe is a 12V 21/5W, I made a typo in saying it was 12V 21/5 amps.

Is this tailight electrical drain a common accurance with Commandos?

Brewer.

Click to expand...

No. A healthy battery and charging system shouldn't dim lights with the brake on. You really need to put a voltmeter across the battery and see what's happening. Maybe you just need a new battery, or maybe it's not getting fully charged.