Successful Electrical Repairs on the Ol' Dual Sport

I'm very proud of myself. Since purchasing my '79 XL250S vintage dual sport, I have since discovered that the 6V electrical systems on these old bikes are notoriously fussy and problematic, especially when it comes to the lights and turn signals. Even with a new, fully charged battery and good connections, it seems like these systems are a bit wonky and unpredictable.

I discovered three main electrical problems with my bike. With the help of an online wiring diagram, and also drawing out my own simplified diagram focusing only on the parts that needed attention, I was able to zero in on the problems. Here are the diagrams:

 

First, the front brake light switch was broken. This is the switch that works off of the handlebar brake lever, and operates by a little spring loaded switch that closes the circuit when you pull the handle to apply the front brake, and opens the circuit when you let it go. Problem was the tiny little plastic stem that allows this to happen was broke off, so the brake light just stayed on all the time (switch constantly closed). I found a replacement on eBay, and it now works as it should. Here's a pic showing the small plastic stem that operates the spring loaded switch:

 

Second problem was that the previous owner had installed new but incredibly tiny rear turn signals that were really just useless. The signals used tiny bulbs like the kind you would use for instrument panel indicator lights. Add to that the fact that this system is a bit dim anyway, and you could hardly see them at night, and not really at all during the daytime. So I put on a new set of the flexible Baja Designs dual sport turn signals, and they seem to blend in nicely with the rest of the bike and are a similar style to the original front turn signals. Here they are on the bike now:

The main issue I had with installation was that the original holes in the metal plate under the plastic fender were not perfectly round, and were therefore not allowing the larger threaded stem of the new signals to slip through. Here's a shot of the oblong, irregular hole:

I ended up drilling it out a bit with a metal drill bit and filing the edges down just enough to let the new stems pass through. I dismantled the metal fender underframe from the rest of the fender before doing this so that I would not ruin any of the other parts or surfaces. Here's me testing new stem fit into the drilled hole...

 

These signals came with the usual 12V bulbs, so I simply replaced them with 6V bulbs from my local auto part store.

Next issue was that the brake light was still misbehaving, even after replacing the front switch and checking all the connections. A little investigation revealed that the ground wire going to the break light housing was loose where it connected to the base of the bulb casing. I ended up soldering it to the outside of the bulb sleeve and routing the ground wire back through the plastic base. Reconnected everything, and that did the trick!

The last problem was that the turn signals would not blink at all, they just stayed on steady. I made sure that the battery was fully charged with my new 6V trickle charger, but that did not make a difference. I have also read that sometimes the signals will not work unless the engine is revving, but that didn't seem to help, either. I removed the stock turn signal relay and took it apart to inspect it. Here is the relay before I took the cover off:

It was rusty, and so I sanded it down a bit and sprayed it with some electrical contact cleaner. Here's a shot of the inside of the relay:

My understanding is that there are two kinds of metals here: the bigger flat plate, and the strip of metal that runs across the back and folds around the corners. The general idea, if I understand correctly, it is that when voltage runs through this switch, these two metals react by bending, essentially working as one big contact switch that opens and closes against a contact point just underneath this plate. I suspect that the low and irregular 6V current, along with the aged and corroded state of these metals, kept the switch from operating the way that it should. I replaced it with a new, round modern style 6V relay, and all turn signals work great so far.

So, all electrical problems seem to be sorted! We'll see how long that lasts. Here's a shot at the end of the day, sitting pretty in the sunset, right around beer-thirty.