47-59 '54 turn signal problem, need diode?

[CoachH]

I installed a new wiring harness on my '54 s10 conversion and both front turn signals were blinking at the same. It was caused by the original gage design only had one light for the turn signals and when both wires are connected it created a loop and made them both flash when either was turned on. I was told I need to install a diode by the wiring company (EZ Harness) but havent been able to find one since all of the radio shacks are closed were we live.

Does anyone know which kind to order online and where to get them? Or does anyone know another way to fix the dual turn signal problem?

Thanks,
Russ