The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Ironhead2 on April 12, 2010, 10:37:31 AM

Title: Generator Light On
Post by: Ironhead2 on April 12, 2010, 10:37:31 AM

I picked up an '83 R65 recently & it seams to have an electrical issue. As soon as I plug in the battery connections the generator light comes on. Even with the key in the off position it stays on. The bike starts & runs but I am only getting around 12V off the battery with the bike running. Any ideas on where to start?

Title: Re: Generator Light On
Post by: Bob_Roller on April 12, 2010, 10:54:56 AM

My first guess, would be the diode board under the front cover of the engine .

Title: Re: Generator Light On
Post by: Barry on April 12, 2010, 01:50:03 PM

You have 2 problems

1. The generator light is on with the ignition off

2. 12v at the battery with the engine running indicates the battery isn't charging. You should have 13.8 volt minimum given enough revs.

They may or may not have a common cause. I would resolve No1 first because when I look at a wiring diagram I cannot see any way that the generator light could come one with the ignition off unless you have a wiring fault. I would check the wiring carefully against a wiring diagram for your model. Check for a voltage to earth on both sides of the generator light with the ignition off.  Your going to find a voltage on one side or the other which should lead you in the right direction to trace the fault. It is possible for leaky diodes to put a voltage on the left hand side but there would still need to be an earth fault in the wiring from the ignitions switch. I think it more likely you'll find the voltage on the ignition switch side of the lamp due to incorrect wiring. I don't have a diagram for an 83 but here's an excellent one for the charging circuit.  (http://)

Title: Re: Generator Light On
Post by: Bob_Roller on April 12, 2010, 02:28:05 PM

About the only way I can see it happening, is to have two diodes fail on the diode board, in the 'shorted' mode, allowing current flow in both directions .

Not a common failure to say the least .

But one good 'mishap' with the front cover on the engine, touching the diode board, with the battery connected, is all it takes .

Who knows what the previous owner(s) may have done !!!!!

Title: Re: Generator Light On
Post by: Rob Valdez 79 R65 on April 12, 2010, 06:13:05 PM

So, as a new owner, you should understand that you should disconnect the ground wire to your battery EVERYTIME you remove the front engine cover.

Title: Re: Generator Light On
Post by: nhmaf on April 13, 2010, 08:27:49 AM

Actually, what Rob means is EVERYTIME BEFORE YOU REMOVE THE FRONT ENGINE COVER - do not wait to do it afterwards, as it is in the process of removing said cover that this damage commonly occurs.

Title: Re: Generator Light On
Post by: Ironhead2 on April 13, 2010, 09:09:11 AM

Thanks everyone for the good tips. That gives me a place to start.