If you installed LEDs you need to install the correct load equalizer. I had the Kuryakyn Panacea taillight and turn signals. It came with a load equalizer that plugged into the harness and I had no problems on my 2001 FXD.
Kuryakyn sell a couple load equalizer add-ons that have to be wired in:
http://www.kuryakyn.com/products.asp?bn=harley&ci=3292 ($26.69 here at DP)
http://www.kuryakyn.com/products.asp?bn=harley&ci=3319 ($15.12 here at DP)
The other version for you model is a direct plug in module, so no wire cutting:
Smart Equalizer part number: DS06053005 $53.35 here at DP. Here's the write up for it:
Most load equalizers place a load back on your electrical system, this wastes power and reduces the brightness of your LEDs. Smart Equalizers solid state units that trick the load dependent flasher into thinking there is a load when LEDs are present. Consumes less power than typical load equalizers. Smart Equalizers produce little or no heat. Delivers more power to your LEDs resulting in brighter light. Plug and Play. One Smart Equalizer covers the Entire Bike.