Thread: Tail Light Brake Light Issue - 1978 CT90

Hello - new to the forum here. I have a 1978 CT90, and really enjoy the bike. I think I have a problem with my tail light, however. It wasn't working at all, so I opened up the light housing, took the bulb out and then reinstalled it. The first time I did this, the light went on when I turned the key, but it seemed real bright and when I applied the foot brake there was no change in the light. I took it out again, reinstalled it, and then the foot brake activitated the light (but not as bright as when I first put it back in), but there was no tail light. Based on what happened, here are my questions:

Should the handlebar brake lever activate the brake light as well as the foot brake?
Is there a proper way to put the light bulb back in so both the tail light and brake light works?

Thanks for any help!

The bulb has two little metal protrusions that are different depths and the socket has matching slots for them. The bulb needs to go in the proper way, not 180 degrees off. One filament will burn brighter than the other.

Test the bulb on a battery (connect a lead to the brass base and the other lead to each of the contacts on the bottom and make sure the bulb will light on each of the contacts.) If that works, AND you have the bulb in correctly, AND the taillight is plugged into the harness correctly, then it should work correctly.

I am not familiar with that bike specifically, but the above is for all bikes with brake lights.

Your front brake lever will either have a switch in the lever mount (a wiring harness right next to where the brake cable comes out) or it will have a thick spot in the brake cable, about half way down, with two wires coming out of the thick spot. There are other methods that could have been used, but those are the most common.

If you have a connection like that, and it does not activate the brake light, but the foot brake does, then you have a disconnected or broken wire between the front switch and the light.

You can also test the socket by connecting a test light to the frame then with the key on, touch each of the metal connections in the bottom of the socket (don't touch the socket itself). One will be "on" with the light switch, and the other should be "on" with the brake lever depressed.

With wiring, you need a wiring diagram, then start at the non-functioning part and work back through each segment until you find the break. There really is not short cut.

Thanks makotosun - this is very helpful. I'll check these out!