My turn signals work, and my lights work, but when my lights are on, my turn signals will not work.

This is a classic bad ground problem.The problem is that the light sockets themselves are not grounded properly or at all. For anything electrical to work properly, you must have two (2) things, a 12-volt feed and a ground. The bulb usually picks up a ground through the case of the bulb, but in this instance it’s picking up an improper feedback ground through the opposite wire in the light socket itself. The reason the turn signals quit working when the lights are on, is that a 12-volt signal is now being sent down the opposite wire, which was acting as a ground before. Once the lights are turned off, everything will work fine again.

Solution: Be sure that whenever your lamp is grounded, you have a good known chassis ground. This usually involved scraping paint or rust from the mounting surface and, in extreme cases, running a separate ground wire to the lamp assembly itself.