Diode Selection

Hello everyone, I'm a retired mechanical engineer which make me even more stupid, I need help with selecting a diode which I hope will solve my problem. I’m looking for advice on selecting a diode for my turn signal for my motorcycle dash conversion. The turn signal dash light wiring does not use a typical ground, the circuit uses the opposite turn signal circuit power wire as ground. I know this might seem confusing it was to me until I found a YOUTUE video on the subject. As I understand it, the dash light bulb draws so little current it doesn't "luminate" the actual opposite turn signal itself. My digital dash has the same visual indicator as on my old analogue dash a double arrow pointing in opposite direction similar to a hazard light, in fact I think it is intended to be used in that manor. So, here's my question, my digital dash must use it's own internal ground and I have two wires from my switch which I plan to tie together however it will light all my turn signals if I simply connect the wires so I think a diode in each switch wire before the connection will work for me however I have no idea what type and size I should install, can someone help me.