I have a 2006 Heritage Classic. I found out I had no tail lights. The lights on the sisy bar are also out. Checked fuse box and found blown fuse. Replaced it, but it blew again next day. Brake lights and turn signals are working fine. Any idea where to begin my search? I had recently lifted the tank a couple of inches to run the wire for a tuner. Did I pinch a wire?

 

Seems like you have a short if the fuse keeps blowing. Start checking the wiring under the tank. Considering the work you just did it's a good possibility something is rubbing or pinched.

 

Just checked for pinched/cut wires under dash and under tank. Did not find any evidence of damage. All wire bundles are protected with a plastic channel or conduit. Used light probe to check one side of blown fuse. It was getting power. The other side was of course, no getting power. I checked again with a multi meter, with and without the fuse. It is getting 12 volts. Since the lights on the sissy bar are also affected, I checked the wire harness and it too was getting 12 volts. What I am wondering is why the sissy bar is being affected, since the harness is wired between the fuse block and the harness to the rear fender. Suffice it to say that I checked both harnesses, and did not find any wire damage. How can I find out at what point there might be a break in a wire?

 

Can someone please take me to school? When a mini fuse blows due to a short in the wiring, is it possible to tell from the element in the fuse which side of the wiring the short might be located? Let me explain.

A fuse has an upside down, U shaped element. When it blows, most of the time, the area where the element broke is to one side or the other within the plastic body of the fuse. Almost never evenly in the middle.

Based on where the breakage occurred in the element, is it possible to tell where the short might be located? In my case, the element broke on the "downstream" side of the fuse ( for lack of a better word) which powers the wire harness into the rear fender.

The "upstream side" of the fuse still had 12 volts going to it. Is it safe to assume that the problem then, is isolated to the wiring on the "downstream side," meaning the wiring harness that goes directly to the rear fender, since that is the side on the fuse that does not have 12 volt power? I hope my layman's terms can be understood by those who are more savvy than I am. Thx.

 

The fuse protects the wire after the fuse, that is why the fuse is located as close to the battery as possible.

The circuit that is giving you the problem is the lights circuit, it powers the tail lamp and the running lamps up front (in the turn signals).

Try to narrow it down...

Disconnect the connector to the rear harness, if the fuse still blows, the rear harness is probably not the problem.

Next, disconnect the connector to the front turn signals, if the fuse does not blow, the problem is probably up in that front wiring after the connector.

If the fuse still blows, the problem is somewhere in the main harness, start looking at the blue wire in that main harness.

 

After an exhaustive check of all appropriate wire harnesses, I have ruled out any wiring related issues. I have now confirmed that only when the motorcycle back fires upon starting it, that it blow the lights fuse. The battery is fairly new, so is the voltage regulator and coil, so those can also be ruled out, as well as plugs. The motorcycle has always back fired, in about one out of 10 starts, mostly when cold. It would seem like some electrical surge occurs when it backfires to cause the fuse to blow. I can live with that. I don't want to go down the path of chasing the back firing problem. My question is, what is the best way to separate, and install a switch, so that the power to the blue wire (running lights), does not get power when starting the bike. This would be just like the switch that operates the spot lights, which you have to operate manually. That may not be the correct solution, but would be the least hassle for me.

 

A power surge can burn out bulbs, but it will not blow a fuse/trip a breaker.

A blown fuse is caused by a short to ground.

 

Don't mean to be hard headed, but one second, all is fine with all lights. When it backfires, while the bike is in the garage, the affected lights go out in front of my eyes, at the exact second that the motorcycle back fires. When I check, the fuse is blown. I don't believe that to be a coincidence. Those times that the bike does not back fire, the fuse does not blow. As said, I have tested every inch of all wire harnesses, including disconnecting each one, and testing them under different conditions. Harnesses are ruled out as having a short.

 

The fuse is being blown because the current is finding a shorter path to ground.

The fact that the engine backfires at the same time may not be a coincidence, but I would suspect that whatever is causing the fuse to blow may also be the cause of the backfire (the backfire is not the cause).

There is some issue in the electrical path between the fuse and the bulbs.

Have you looked at the wires up front, going to the front running lamps (blue wires)?

 

Have you or anyone that you know of, done any modifications to the lighting system or any wiring repairs/modifications? If so, that is the first place to start.

I am thinking that the back fire is being caused by a weak or missing spark that is happening when the short pulls the system volts down below the firing system threshold...IOW, the short is causing the backfire...

If you are positive that it is only your brake lights that are affected, then eliminate that first by isolating the problem to the front or rear lights by disconnecting the connector to the rear lights under the seat. If it all works, then you know where to look. If it doesn't, then pull out the front wiring harness from the frame and disconnect the connectors for the front lights and check again. If it is still shorted, then you need to look at the fuse block and turn signal module and wiring.