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Rusty Cage
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Auburn California
Joined: 09/30/2012
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Just finishing up my restore and customization of my 75' R75 /6. Since I've gone this cafe/brat custom style, I want to keep the profile low and clean so I don't want to use the original tach/speedo console. I was thinking about removing the tach and speedo cables completely and using a GPS speedometer. Any tricks to capping off the tach and speedo inlets once I remove the cables?

  • my_r75.jpeg
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1966 R69S - second owner, original condition
1975 R75 /6

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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For the speedo cable, you

For the speedo cable, you could just use the rubber boot and maybe fill it with some thick grease. Not sure about the tach cable...that goes through the side of the case...other than cut it off and put some sealant around it.

What are you using for a charging system? The stock system uses the gen light bulb in the speedo pod as part of the charging circuit. Without it and/or some kind of substitute, you won't get any charging to the battery.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Rusty Cage
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Auburn California
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Hi Kurt, I have not heard

Hi Kurt,

I have not heard anything about this in terms of the charging system running thru the instrument panel. I only just now got it running smooth and have not taken it for a real ride yet, so the charging has not been road tested. Do you know of any ways around the instrument panel. Also curious if an earlier 70's model headlight would work, with the tach/speedo built into the headlight housing? Currently, I'm not running any instrument panel. It is disconnected and the speedo and tach cables are just sitting up behind the headlight. Thanks for your help, .....would have been a real drag to go for a first ride and get stranded.

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1966 R69S - second owner, original condition
1975 R75 /6

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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I'm pretty sure that all

I'm pretty sure that all Airheads '70-on need the resistor in the instrument panel to feed the alternator for proper charging. But there is a way around it. This webpage talks about how to wire in a resistor to bypass this light. The bypass is more for the situation where the light fails while on a trip, and the resistor then keeps things going until you can get back.

http://bmwmotorcycletech.info/genlampresistor.htm

The light is a good feature IMO. In normal use, the light comes on full bright with key on, engine not started. The light should go out when the RPMs get above 1500 or so...it shouldn't come on again above that. If you see the light come on at other times, it's a quick indication you have a charging problem. Without this indicator, as in the case of the resistor bypass, you won't know if you're actually charging or not. About all you can do is put a voltmeter across the battery terminals and rev the engine once in a while. If the voltage rises to above 13.5 to near 14, then your alternator is working.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Rusty Cage
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Auburn California
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Thanks a lot for the info.

Thanks a lot for the info. I'll put the instrument panel back on until I can come up with a good alternate solution.

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1966 R69S - second owner, original condition
1975 R75 /6

mark_weiss
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Arizona
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Either the charging bulb, or

Either the charging bulb, or an equivalent resistor (3w?) should be in place for the charging system to function properly. With the bulb removed and the circuit left open, the rotor will not energize and there will be no charging.

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Mark
qualitycycleservice.com

Rusty Cage
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Auburn California
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Resistor mod done

I followed the guide on the link you provided and used a 360 ohm resistor between the coil and the voltage regulator. So it should be good to go. Thanks for the heads up, you saved me a lot of hassle from potentially being stranded on the side of the road. So now i'm on to removing the instrument panel and cables.

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1966 R69S - second owner, original condition
1975 R75 /6

Rusty Cage
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Auburn California
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I completed the resistor mod

I completed the resistor mod #2 as listed in the write up on the link you attached. I wired a 360 ohm resistor between the left coil and the voltage regulator attached to the wired and connector they described. What I'm not clear on is, when testing with a voltage meter, should a meter show a difference in charging when the bike on vs off? When I hook it up to the DC meter, it doesn't seem to change much between running and off. But that may be correct, yes? The gen light only comes on when the bike it at low RPM, then it goes off once the RPM goes up. That implies less or no voltage going thru the light at higher RPM, right? I'm not an electrical guy so if any one knows the answer, that would be helpful.

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1966 R69S - second owner, original condition
1975 R75 /6

schrader7032
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San Antonio, TX
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There likely won't be much

There likely won't be much charging with the bike idling. As you indicated, in the standard configuration with the light, it will be on at low RPMs which is basically indicating no charging. When the light goes out and RPMs get into the 3000 to 3500 range, then you should see charging. If things are working, you should get well north of 13.5v with higher RPMs.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Rusty Cage
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Auburn California
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Posts: 56
Thanks Kurt. I'll test it

Thanks Kurt. I'll test it out and see what I get.

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1966 R69S - second owner, original condition
1975 R75 /6

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