New to forum. Have 98 FXSTS.
Rear running lights don't come on. Back tail light comes on. Checked bulbs on front and rear running lights, both OK. Checked breakers, OK.
Front running lights work, as do front and rear turn signals.
Where do I check next?

 

Not sure on your year, but are you positive your rear aren't turn only?
My 94 Softail only has running light in the tail light, Strut lights are turn signal only.

 

…..I just checked my sportster, and the strut lights on that bike don't come on either…brain fart….
..thx for the sanity check..

 

but the rears can be turned into running lights very easily

 

The turn signal to brake lights is a great modification. Try for the one that also gives you running lights. Both my bikes have it, one is turn/brake only and maybe module was just older version. Either way they really make you much more visible night and even day.