Lights dimming when brakes applied???

[Qumodo]

Has anyone ever encountered the problem if the bikes lights dimming when the brakes are applied? I'm hoping for some advise before I go tearing through the wiring.....Thanks!

 

[Steve]

Is the engine running when you notice this? What RPM?

Actually, let's back up a bit. You did mention "bike". I am going to presume it might even be a GS because you are on a GS forum. However, we really would appreciate a clue to what bike you are asking about.

.

 

[Qumodo]

The bike can be running or not, it happens in both situations, and yes it is an 82 GS850.

 

[fbody_mike]

At idle it is normal from my experience. Does it do it with the motor revved up to? You should check out the charging system on an old GS periodically in any case. There is the test in the manual or the one on this website are good.

 

[posplayr]

The obvious thing to do is check if the battery voltage is dropping when applying brakes (and/or the voltage at the lights). Act accordingly.

 

[Qumodo]

The battery voltage does drop from 12.5 to 11.9 when the brake is depressed, the charging system was replace a few months ago due to the notorious GS issue, bot the stator and R/R are new.

 

[posplayr]

The battery voltage does drop from 12.5 to 11.9 when the brake is depressed, the charging system was replace a few months ago due to the notorious GS issue, bot the stator and R/R are new.

Is that with the bike running?

PS you might want to do a Quick test and report all 6 numbers. Changing parts does not guarantee that the charging system is working.

 

[Qumodo]

It was not with the bike running, I will go out and run the test and report back

 

[posplayr]

It was not with the bike running, I will go out and run the test and report back

Then you battery is at a low state of charge meaning you are probably not charging very well.

 

[Qumodo]

Here are the numbers from the test.

1.) key off................12.7
2.) key on .....12.2

3.) at idle 1500 rpm.....12.9

4.) at 2500 rpm.......13.2

5.) at 5000 rpm.....13.7

6.) key off.....13.2

 

[posplayr]

Here are the numbers from the test.

1.) key off................12.7
2.) key on .....12.2

3.) at idle 1500 rpm.....12.9

4.) at 2500 rpm.......13.2

5.) at 5000 rpm.....13.7

6.) key off.....13.2

You never listed yoru bike.
Is 2.) key on with headlight on?
It seem like the battery is under charged or weak.

At 5K RPM you should be closer to 14.5V unless:

Bad connections at the R/R.
Bad battery
under charged battery.

You are kind of in the middle. Do the Stator Pages Phase A voltage drop tests at 5K RPM.

 

[Qumodo]

I listed my bike a few posts back but is a 82 gs 850, I found this forum when i came across the stator pages, it was that issue that led me to realize that my old R/R was bad, I replaced the stator and R/R with new components. This issue also just started a few days ago. I replaced the Stator and R/R months back and havent had issues until this week. I will go conduct the phase a test and report back... i guess its possible something went bad

yes test #2 was with the headlight on

 

[posplayr]

I'm looking for something to explain the low charging (13.8V at 5k RPM). That surely will lead to a weak battery although the step 2.) of the quick tests the battery looks good under the key load (with headlamp) looks good.

It is also possible that part of the problem is dirty connections to the brake lights.

There seems to be several factors at play most of which are easily fixed (i.e. dirty connections or fresh battery or charge)

 

[posplayr]

I listed my bike a few posts back but is a 82 gs 850, I found this forum when i came across the stator pages, it was that issue that led me to realize that my old R/R was bad, I replaced the stator and R/R with new components. This issue also just started a few days ago. I replaced the Stator and R/R months back and havent had issues until this week. I will go conduct the phase a test and report back... i guess its possible something went bad

yes test #2 was with the headlight on

People are requested to put the bike in their signature for easy reference.

 

[Qumodo]

I'll add my bike to the signature..no problem! here are the results of the testing i just conducted.

Out of stator @ 5K rpm
Phase 1: 79 ACV
Phase 2: 77 ACV
Phase 3: 80 ACV

From R/R : 4.6 DCV at idle 2.9DCV @ 5K rpm

The taillight is new as are the connectors, I do believe this started after the new taillight installation but I cannot figure why???? it is three wires, all new connectors with dielectric grease and heatshrink

 

[posplayr]

I don’t understand the r/r vdc numbers?
what are you measuring?

 

[Guest]

The battery voltage does drop from 12.5 to 11.9 when the brake is depressed, the charging system was replace a few months ago due to the notorious GS issue, bot the stator and R/R are new.

What type of RR did you install?

 

[Qumodo]

measuring the output of the R/R, positive lead to the red line out of R/R, negative lead to ground on frame.

 

[Qumodo]

it is a Caltric R/R

 

[Steve]

Here are the numbers from the test.

1.) key off................12.7
2.) key on .....12.2

3.) at idle 1500 rpm.....12.9

4.) at 2500 rpm.......13.2

5.) at 5000 rpm.....13.7

6.) key off.....13.2

It seem like the battery is under charged or weak.

At 5K RPM you should be closer to 14.5V unless:

Bad connections at the R/R.
Bad battery
under charged battery.

13.7 volts at least shows that there is <some> charging going on. :-k

How soon after starting the bike did you read that 13.7 volts? If the battery is low (even though it shows 12.7 at the start), the effort of starting the bike might take a while to charge the battery. It won't show 14+ volts instantly, it may take a few minutes of riding over 3000 RPM to get it up there.

The stator numbers look good, but your Vdc numbers are TERRIBLE. You either were not measuring correctly or the R/R is faulty. It does not really matter which, you will do yourself and your bike a favor if you replace your R/R with an SH775.

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