2009 Heritage turn signal problem.

[BB]

I just bought a 2009 Heritage . Found left turn signal will not work some time. Also seen when it will not work the red security (key light) is on . Any ideas?

[Fugawee]

Is it the entire left side?  Or, just the Front or Rear?  Does the indicator light for the T/S light up on the Dash Panel?
Are You certain that the Bulbs are OK?  And, no problem with the Right Side?  Has anything been done to the Handlebars, such as replacement?  Or the Controls?  Gas Tank removed for any reason?
I would start out checking the Bulbs, and the Bulb Sockets for corrosion, bad ground, etc.  After that, the Switch You put Your thumb on to activate the T/S for the same, or a loose/broken wire.  Wire for the Left Side Controls may be pinched at the Housing, or grounding out on the H-bar, where they attach to the H-bars, if the H-bars, or Controls may have been worked on, or replaced.  The Left Side Controls harness should be under Your Gas Tank on the left side.  Removal of the Gas Tank could be, and probably will be necessary for access.  There is also a connector under Your seat, near the Rear Fender that feeds the Rear Lights.  You may want to take a look at that as well.
A Test Light/Probe to "ground/negative" should be able to help You out for the indication of Power/Flashing of the circuit.
A Test Light/Probe to "hot/positive" should be able to help You out for the indication of a Bad/Missing Ground.
A little bit of Di-electric grease on the Bulbs/Sockets won't hurt to control/limit any corrosion.  Cleaning up the Sockets with a little Emory Cloth, or a very Small Wire Brush should be done prior to the Grease.
Good Luck!

I seem to have focused on the T/S, and not the Security Light.  Are there any codes popping up in Your Speedometer?  How to access the Codes should be in Your Owners Manual, or Service Manual, should You have one or both.  A code may tell a different story.

[Coyote]

Since you have a lit key, You should pull the diagnostic codes.

https://harleytechtalk.com/htt/index.php/topic,53211.0.html

[Hossamania]

Start with the bulbs.

[Appowner]

With regards to the security key light.  Is it already on BEFORE you try to activate the turn signal or does it come on WHEN you try to activate the turn signal?  And to clarify, does it come on every time you try to activate the left turn signal?

Sounds almost like it's the security key circuit that's waiting/asking for the PIN to be entered.  The left signal button is used for that.  But by all means, check the easy stuff first.  Clean sockets etc.

[Hossamania]

Not sure if it works the same, but on my '01, the key light would stay off until I turned the signal light on, then would light up. This indicated a burned out bulb.