Attached is the link to a recent discussion about sources for wiring harnesses for our early Fords. I found post #33 especially helpful since it came from one of our trusted vendors.
https://www.fordbarn.com/forum/showt...ghlight=wiring
I would want to make some modifications to the stock wiring harness for a 1937 to add turn signals both front and rear and add a ground wire for each headlamp assembly. I am sure the harness suppliers have already considered these modifications and maybe some others. I have not spoken to anyone about harnesses yet.