Brake Light will not turn on when front brake lever used 74 R90s

[dimitri0411]

Hi, I just purchased a 1974 R90S and noticed that the rear brake light will not turn on when front brake lever is pressed only when rear brake pedal is used does it work. The brakes engage when I use the front brakes. Any quick fix recommendations? I'm Fairly new to Airheads

 

[20774]

Your bike has the undertank master cylinder. Typically off the front of that is an electrical connector which indicates when the pressure builds in the master cylinder. You should check for that and be sure that the connector terminals are clean.

I also remember maybe a switch at the right lever? Should confirm that.

 

[dimitri0411]

Your bike has the undertank master cylinder. Typically off the front of that is an electrical connector which indicates when the pressure builds in the master cylinder. You should check for that and be sure that the connector terminals are clean.

I also remember maybe a switch at the right lever? Should confirm that.

thank you I will check those

 

[r65_steve]

I just had this issue on mine (81 R100). In my case, I think the little switch at the lever had some gunk on it. When you'd pull it, it wouldn't open the circuit to trigger the light. I took it out several times and shimmed with a washer. (Then it was on full blast). Finally put it back together and it worked fine. A mechanical problem manifesting as electrical. Take the switch out and clean everything really well...easy to do with minimal effort.

 

[m_stock10506]

Hi, I just purchased a 1974 R90S and noticed that the rear brake light will not turn on when front brake lever is pressed only when rear brake pedal is used does it work. The brakes engage when I use the front brakes. Any quick fix recommendations? I'm Fairly new to Airheads

61 31 1 351 662 STOP LIGHT SWITCH
Stop light push button switch, R50US - R69US; R50/5 - R90S. Fits all /5 (front brake) and 1974 /6 (front brake and clutch).

Up at the right brake lever, this switch is screwed into the lever assembly with a black rubber boot covering most of the switch and the wire terminals. This part is listed in the /5 parts, but the text says that it also applies to the 1974 /6 models. If you look in the Max BMW parts fiche you will see a few photos. I have a 1974 R60/6 and I had to replace this switch. Once you locate it, it's not hard to remove. After nearly fifty years, the boot will probably tear when you try to remove it. It's a plunger type switch and you could try to get some electrical contact cleaner/lube into the switch to get it working again. I did that with mine but it stopped working again soon after, so I bought a replacement.

 

[dimitri0411]

I just had this issue on mine (81 R100). In my case, I think the little switch at the lever had some gunk on it. When you'd pull it, it wouldn't open the circuit to trigger the light. I took it out several times and shimmed with a washer. (Then it was on full blast). Finally put it back together and it worked fine. A mechanical problem manifesting as electrical. Take the switch out and clean everything really well...easy to do with minimal effort.

thank you will try that.

 

[dimitri0411]

61 31 1 351 662 STOP LIGHT SWITCH
Stop light push button switch, R50US - R69US; R50/5 - R90S. Fits all /5 (front brake) and 1974 /6 (front brake and clutch).

Up at the right brake lever, this switch is screwed into the lever assembly with a black rubber boot covering most of the switch and the wire terminals. This part is listed in the /5 parts, but the text says that it also applies to the 1974 /6 models. If you look in the Max BMW parts fiche you will see a few photos. I have a 1974 R60/6 and I had to replace this switch. Once you locate it, it's not hard to remove. After nearly fifty years, the boot will probably tear when you try to remove it. It's a plunger type switch and you could try to get some electrical contact cleaner/lube into the switch to get it working again. I did that with mine but it stopped working again soon after, so I bought a replacement.

thank you for this as well. will look at that switch!

 

[RPGR90s]

Hi, I just purchased a 1974 R90S and noticed that the rear brake light will not turn on when front brake lever is pressed only when rear brake pedal is used does it work. The brakes engage when I use the front brakes. Any quick fix recommendations? I'm Fairly new to Airheads

As others have pointed out, the front brake lever on a '74 R90s uses a large plunger switch mounted to the lever. Pull back the boot and check the two wires that screw into the switch. Unless the wires are tinned (soldered), they can get green and crusty and not conduct very well.

As the switch can be a little expensive, check its resistance with an ohmmeter first before replacing. You should have zero ohms (closed) or infinite ohms (open). I've replaced a few on my '74 over the years and resistance starts to change sporadically when acting up and that's when I replace it.
it
Lastly, verify that the switch opens and closes with an ohmmeter when the lever is pulled. If not adjusted correctly, it won't activate.