This is a write-up about an old repair that I though I'd talk about just in case someone has the same issue in the future.

My front turn signals went out only when my fog lights were on. Upon inspection I noticed that even with the fog lights off, the turn signals were rather dim. The bulbs were fine.
So it seemed like the front lighting assemblies were not getting enough current. I followed the connectors back and sure enough, the electrical connectors in the sides of the front bumper that supply the turn signals and fog lights were heavily corroded. Green sludge covered the pins.
I cleaned them out with electrical contact cleaner and then packed them full of dielectric grease to get a better seal (I couldn't find new o-rings). The repair has held for over a year with no signs of failing.

What had happened was that I had removed the bumper for a repair previously. These junctions were disconnected. When I put them back together, they were so dry and the o-rings so old that they ripped. Then water made its way in and you know the rest.
So, moral of the story: lube your o-rings when putting electrical connectors back together and pack in some di-electric grease for safety.