So, I thought all my problems were solved with my turn signal lamps on my ‘38 by using LED park/turn signal globes up front and standard globes at the rear in a seperate lamp. (Not though the brake lamps ) These are 6volt double contact LEDs and work fine when tested on the battery.   What happens when they switch on either left or right is that both front turn signals flash along with the rear of that side.   It seems that the power is feeding bac