Run-n-Lites & K-Tail-2 effect on charging

[Dan Kearney]

Greetings All,

I recently installed front and rear Run-n-Lites and the rear K-Tail-2 lighting enhancements on my 1987 K75. Yesterday was the first time that I have had the opportunity to ride the bike after dark.

I noticed that while sitting at a stop light, idling at ~950rpm that the alternator's idiot light was glowing very, very faintly. The bike has never exhibited this in the past.

If I engaged the brake, it would glow just a tad brighter, but still faintly. As soon as I revved the motor a bit it would go out and remain out as I rode.

Is this a coincidence of the added draw on the system, or should I investigate further? If I want to check my alternator's output, at what point should I connect the multimeter leads to get an accurate reading?

Thanks,

Dan K.
Denver

 

[jdiaz]

My K75 is equipped the same way and shows the same glow. No worries.

 

[Dan Kearney]

Jon,

Thanks for the reassurance.

Dan K.
Denver

 

[kioolt]

I had the same thing with my 91 K100LT at idle. I didn't let it bother me. I did however change my alternator to the 700 watt that is installed on the newer bikes. I had my battery go dead on me twice while pulling my trailer and running two electric vests. After installing the 700 watt alternator I never had anymore trouble while pulling the trailer.

 

[Dan Kearney]

Any idea if one of those alternators would work on the K75?

Dan K.

 

[kioolt]

K100's and K75's can use the same alternator. Even the oilheads use the same alternator. To use the 700 watt alternator on your early K75 you will also have to get the coupling that goes between the alternator and the engine because the 410 watt alternator and 700 watt alternator have different size shafts. You will also have to make a short piece of heavy gauge wire to go from the alternator to the battery.

I believe that the later K75's came standard with the 700 watt alternator. If I'm not mistaken it was changed to 700 watt in 91 or 92.

 

[Dan Kearney]

Thanks for that info! I must begin my quest for a new alternator now. Do you by chance know if the two are clearly differentiated by labels or shape?

There seem to be a lot of K75 parts up on the IBMWR marketplace, but I'd like to be certain of purchasing the correct one.

The coupling that you speak of, is that the thingamabob that has the rubber inserts in it?

Thanks for the help.

Dan K.
Denver

 

[jdiaz]

Well, the swap isn't a slam dunk. The 700w alternator is longer, so I think a different coolant overflow bottle and longer hose would be required. My '95 K75 was different than my '88 K75 in this respect.

 

[kioolt]

The coupling that I am speaking of is the thing with the rubber pieces in it. The reason you need to change that is the shaft size on the two alternators is different.

Yes they are marked. I believe the 410 is marked 33 amps and the 700 is marked as 50 amps.

When installing the 700 on my 91 K100LT I did not have to change the coolant bottle. This may be different on the K75's. I did have to make up a cable to go from the battery to the alternator.

 

[Dan Kearney]

Thanks everyone for the excellent information.

Dan K.
Denver

 

[deilenberger]

The coupling that I am speaking of is the thing with the rubber pieces in it. The reason you need to change that is the shaft size on the two alternators is different.

Yes they are marked. I believe the 410 is marked 33 amps and the 700 is marked as 50 amps.

When installing the 700 on my 91 K100LT I did not have to change the coolant bottle. This may be different on the K75's. I did have to make up a cable to go from the battery to the alternator.

The 700W jobbie has a BIG black cover all across the back. And you don't have to change the coolant bottle - you do have to change the connectors to the alternator - the 700W one uses ring-connectors. Easy to find and do.

AFAIK.. you'd only have to change the coupling IF the new alternator didn't come with the cup drive for the coupling. In looking at them - the cups appear to be identical (but perhaps the shaft size going into them is different).

 

[Dan Kearney]

Thanks Don,

Now, if I could just find one. No luck so far. And to make matters worse, my girlfriend had added to the draw on my bike with an additional Gerbing vest and socks...

Dan K.
Denver

 

[kioolt]

The 700 watt atlernator used on the oilheads is the same one that is used on the K1100s. I bought myselft a spare from Ebay. It will fit my 91 K100LT or my 04 R1150RT with the appropriate coupling. The K bike will use the rubber insert type of coupling and the oilhead will use a pully.

 

[Dan Kearney]

K100LT,

Thanks for the additional information. I can expand the scope of my search with it.

Cheers,

Dan K.
Denver

 

[deilenberger]

K100LT,

Thanks for the additional information. I can expand the scope of my search with it.

Cheers,

Dan K.
Denver

Oh - one thing Dan.. if you're hoping the larger alternator will fix your glowing charge light at night - it won't.

I have the larger one in my '87 K75S, and have the same light setup you do.. it does exactly the same thing as yours.

This is a FEATURE (well - BMW did have a fix for it wayback.. which was adding an inline diode to one wire in the harness.. my old wiring harness had this and the light never glowed. I didn't bother moving it to the new harness after mine melted down since I wanted the new harness to remain a virgin).

Think of it this way - the dim glow tells you that the charge indicator light isn't burned out. It's a FEATURE!

 

[Dan Kearney]

Don,

No, I forgot all about the alternator light glow. Last weekend I rode up to Saratoga Springs, WY with some friends to enjoy the hot springs. Between my girlfriend and myself we had a pair of Gerbing's socks, a vest, a jacket liner, and gloves. That plus two 55 watt aux. lights.

Everything was fine until the next morning when I went out to replace one of the 1157 bulbs that broke a filament. (Most likely a result of the 35 mile GS ride I and my K75 participated in the previous weekend. Yup, the only street bike amongst about 90 GS's )

Well, while checking all the lights and admiring the effect of the Back-Off! brake light module that I also added last week I forgot that the lights were on while I putz-ed around loading the bike.

I didn't think she was gonna start when it was time to leave, and we had to ride the first 20 miles or so with no 'lectrics so I could let the battery get a head start on charging.

That's why I want the 700 watt unit.

Cheers,

Dan K.
Denver