So I'm out checking all my turn signal bulbs and I notice something odd.

2005 FLHRSI

The amber turn signal bulbs up front are 1157A (Amber - double filaments)

When the bike is on, the turn signal bulbs are lit up. Check.
When I signal left or right the bulbs blink. Check.

But .... in both scenarios it's only the upper filament that is lit. The upper being the smaller filament. At no time does the lower (bigger/brighter) filament ever light up.

WTH?

Logic tells me that when the turn signals are not activated, the bigger filament would be lit and when activated, the bigger one would STAY lit and the smaller one would kick in with the blink.

Following that logic, if the bigger filament is burned out, then I'd only see activity when the turn signal is activated. Right?

Bulbs aren't smart enough to to know when one filament is dead so use the other one are they? That just doesn't sound right.

Confused ......

 

Does sound odd. Do you have 3 wires going to each light? Right side Black is ground, Brown is turn and Blue is running light. Left side is the same except Violet is the turn signal.
Have you checked your lights fuse, the blue wire from that fuse should power up the running lights.

 

Sounds like a ground problem.

 

I checked my 2011 FLTRX & the filaments are side by side. The running light is the lower filament. When the turn signals are activated the higher filaments come on. If you figure it out, let's us know what the problem. Are you sure the bulbs are making contact in the socket? Good Luck

 

This may not be the case but, on some motorcycles when there is a wiring problem, (say a ground as mentioned above) the electrical system will "fake" normal operation with one filament. As in a brake or taillight failure; BMWs for many years would sense the low draw (because of the burnt filament) and run the remaining filament as a running/tail light and increase voltage/brightness when the brake was applied.

So I would check the ground and power to the side that's having problems. I'd put money on it.

 

Here are a couple schematics of a 2004. The turn signal positive comes from the TSSM while the running light Positive comes from the lights fuse. They both share the same ground.

 

Ok well I checked and all the fuses are in good shape. Nothing blown.

This is definitely happening on both sides, not just one. Both of the bulbs are making good contact. Push in, twist, feel the little click, no problem. I even switched the bulbs from side to side with the same result. I'm gonna stop on the way home today and pick up 2 new bulbs just to rule that out.

I've never in my life ever had to find a "ground problem" and don't have a clue as to how to do that. Give me a computer and I can troubleshoot and fix those all day long. When it comes to electricity, the extent of my knowledge is taking that light pen you get from Home Depot and touching a wire to see if it's hot.

Is tracing a "ground problem" something that I should take it to someone?

I looked at the schematics and my first thought was ....

 

Ever follow a car that has both tail lights on, then applies the brakes, one side gets brighter and the other side goes completely dark?

...Ground problem. (in that scenario)

It had found a path to ground through the unused filament...until it was taken away by applying the brakes.

 

That's funny

If you look at the first schematic and find the turn signals you see each one has 3 wires. The black wire is the ground and I can't remember if it isn't attached to the turn signal housing. If it is make sure both are clean and tight.
Follow the wires from the turn signals, ( on the schematic), and go up to the top of the page to connector 31B. Look at the second schematic and in the lower left corner you see connector 31A,(the other half of 31B), and you can follow the Br and V wires to the TSSM. BE wires to the Ignition fuse and Black ground wires to ground.

How did you check the fuse? Do you have a voltmeter?

 

Just to check for a bad ground, you should be able to take a piece of wire, with the insulation removed from both ends, and hold one end on the chrome spot light housing (that should be a good ground) and the other end of the outside of the metal socket that the run/turn bulb goes into.