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Howdy Gang,

TLDR: The tail/brake light on my 1970 R75/5 only ever turns on when I apply my rear brake. Is this an issue?

This may be an incredibly stupid question, but I'm pretty new to this. My 1970 R75/5's tail light only ever turns on when I apply my rear brake. My clymer manual says that 1970 models do not have a front brake switch, but I found a wiring diagram that has a front brake switch on it, and there appears to be a switch on my front brake lever. The tail light also does not come on during normal operation, even when my headlight is on.

1) Should my brake light come on when I apply my front brake?
2) Should my tail light be on during normal operation or at any time other than when my rear brake is applied?

Thanks for the help. Sorry if this is a dumb question. I wasn't able to find anything that answers this question, probably because it's so basic.

Hi,

1) a /5 didn't have a front brake light switch, certainly in most territories. It's possible one was fitted due to local laws. Certainly, the /6 wasn't universally fitted... my /6 didn't have one (but I fitted one). I think it would be reasonable to asume that, if the front brake doesn't bring on the brake light, there probably isn't one fitted. The only way to be really sure is to examine the mechanism... on a cable braked bike like the R75/5, the switch would likely be on the brake lever mounting. That doesn't address the fact that, in the last fifty odd years someone may have made changes to the bike. OK, not entirely helpful but the second point is easier...

2) On a bike of this age, the rear light should be on all the time the light switch is on... The bulb has two filaments which are powered independently.

Treat both issues independently, the first issue can't be resolved without knowing whether your bike has the switch. This can only be ascertained by examination.

As to the second...

The first thing to check is whether the bulb is good (both filaments). It could be that simple.

Check the ground to the rear light cluster... a bad ground can cause a multitude of sins.

Is your bike of the age to have fuses? If so check that they are good.

If all that checks out, you need to trace the wiring back to source. One useful diagnostic is to see whether the sidelight (Parking light, front marker, whatever you call it where you are) and the instrument illumination lights are working. If they're not, that suggests a problem between the switch and the connection board. If it's just the rear light, it's probably just the wiring from the connection board and the light cluster. Working with a test lamp or meter, it should be fairly easy to track down where the issue lies.

Can't really say much more without knowing how competent you are with electrics. If you're completely in the fog, then it's probably a good idea to let someone else take a look.

Rob