dimming lights

Information and questions on GL1100 Goldwings (1980-1983)
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dimming lights

Post by nedntrish » Thu Jun 30, 2011 11:52 pm

Can anybody tell me why my headlight and dash lights dim when i hit the breaks on my '85 1200gl?

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Steve F
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Re: dimming lights

Post by Steve F » Fri Jul 01, 2011 8:35 am

I'm assuming you mean BRAKES? Your lights are dimming beacuse the brake lights are coming on, and the voltage to other things drops because of the added load.
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Re: dimming lights

Post by virgilmobile » Fri Jul 01, 2011 10:50 am

With the engine off,key on,measure the voltage at the 2 battery posts to get a reference.Step on the brake and measure again at the 2 posts.It shouldn't drop only 1/2 volt or so.If it drops a lot more,the battery should be load tested , the ground lug on the frame cleaned , the dog-bone fuse replaced and the 3 yellow wire plug from the alternator modified.

step 2..Start the bike,hold at 2000 rpm,measure the battery voltage after 2 or 3 minutes.It should be somewhere between 12.8-14 volts.If not the charging system needs tending to.
With it still running,step on the brake and look at the voltage.Again it should drop only about 1/2 volt.

The charging system should provide enough voltage AND current to run the bike(10 amp),and enough left over to charge the battery.

If the charging system is weak,or the battery /grounding is bad,the voltage will drop causing dim lights.

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Re: dimming lights

Post by WingAdmin » Fri Jul 01, 2011 12:05 pm

When you hit your brakes, the brake lights draw 4.5 amps, or 54 watts to light up. When your bike has a limited amount of power to begin with, that's not an insignificant amount. Your headlight itself uses 55 watts on low beam, so think of it as switching on a second headlight. If your bike is at low RPM, it means it is not generating enough power to run the bike and charge the battery - so the battery is being drained to run the bike. Switching the brake lights on puts an added draw on the battery, so the available voltage drops, which means everything else dims a bit. How much the voltage drops is going to be a function of the overall health and charge state of your battery, as well as the condition of various electrical connections.

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