Turn Signal/Tail Light Problem

[Rockn73]

I have a 73 Chevy stepside.  Turn signals work fine.  All the lights work fine.  But when I turn the signals on and then turn the lights on at the same time, the turn signals stop.  When I turn the lights back off, the signal starts again.  Same thing if I turn lights on then signals, I get no signals.  Same on both the right and left.  I narrowed it down to the tail light bulb.  When I have the lights on and turn the signals on, the signals don't work.  When I pull the tail light bulb out, the signal works.  The left tail light is grounded to the metal plate in the plastic housing.  The right side is grounded to the light bulb holder inside the plastic housing.  All the relays and fuses are good.  Can anyone help?

[beastie_3]

I might be concerned with how the lights are grounded.....but my truck already had custom lights so Im not sure. I dont know why the lights are grounded two different ways.

[Rockn73]

I just read that my tail lights are for 1977-87 models.  Still need help though.