Does anyone know what each wire is?
I think I see
1 - black with red stripe?
1 - brown?
1 - black
1- yellow

looking to wire the later receptacles that are the twist lock type I think

 

I think you're gonna find that:

• black with red stripe is back up light hot.
• brown is tail / tag / /marker lights hot
• black is ground
• yellow l(ikely has a thin black trace), is left signal / brake hot
• green is right side signal / brake hot

 

Thanks
is there a way I can map these wires
to the later twist on types for 75 trucks
that have red/white/black wires?

 

Looks like the black is still gonna be the bulb ground, but I'd verify it for continuity with the brass contact inside that rubs the bulb base. It will be obvious looking in the socket.

On the bulb, there are two obvious contacts, one will be to the hotter filament, the fattest one which will draw the most amps for brake or signal ... and the other will be to the finer filament that will draw the least current for a dimmer light for just tail light. You could verify which is which using a real bulb and a battery by connecting the verified ground and either the red or white?.

Then splice accordingly.

 

Thanks
yeah I assumed the solid black would be the common ground. Seems like the backup light
would be the easier one.
unfortunately my Backup light is not working due to the neutral safety switch being jumped.
something else to fix 😁
I can definitely use a voltmeter on the bulb sockets to see what values I get
I’m assuming the backup light is grounded to the housing?

 

On mine, the backup bulb is a totally separate bulb. Yes, on a '73 with metal reflector, BU would be grounded through the black wire, so the whole deal is gounded. With a later plastic sealed housing, like my '77, both twist in sockets get a ground wiire too.