rear blinkers don't work when headlights are on

I have a question. I have a 1992 GMC Jimmy with 98k miles. I just replaced all the blinker bulbs in the rear. (2057 and 194) But when I tested them, they worked fine without the headlights, with or without the the brake pedal. But when I turned on the headlights, neither side blinked.
Any suggestions?
BTW: The front ones still blinked with the headlights on.

Sounds to me like you have a wiring problem somewhere. I have had the same problem. At night when I turn my headlights on, my radio goes out. I asked my dad to help me out with this problem, we looked over the wiring and discovered some faults. Overlook the wiring, if that doesn't work then go to an autozone or something.

Mine does the same. When my headlights are on my CB go's off. With the ignition off and the headlights on my stereo comes on. LOL lots of headlight problems

had a very similar problem on a 2001. i tried one of those aftermarket led bulbs ro brake/tail/signal on the back, and they never lit up, so i went back to the original bulbs and they worked, as the first thing i did to test them was put on the flashers. everything was fine untill i turned the headlites on, poof, dark. started checking all the fuses, cb;s, etc, and no blown fuses, in the dask box, or the under hood fuse box, that had anything to do with lites. so i started wth the upper right fuse and worked my way down each fuse untill i found a 10 anp fuse blown. checked the map on the underside of the box lid and it had initials TRLLTL, close any way, anyhoo, replaced it and poof, all lites work in all conditions, etc, back to normal, so i call a gm mechanic at the dealership i bought it from new and he said that the fuse was pre-installed for trailer light, incase someone ordered a trailerhitch, the dealer ship istal's them and just plugs into the harness, but he couldn't figure out why that fuse blew the tail lights out using flashers and headlites.
good luck, and good hunting.
excheezhead.:bigthumb: