1959 GMC turn signal indicator wiring

[Foot Stomper]

So I purchased what seems to be a very well done factory replacement wiring harness for a Chevrolet, because I can't find a GMC one, and they seem to wired almost identical anyway... "almost".

Chevrolet Apache trucks have a left and right turn signal indicator in the dash cluster but GMC are different... they have only one turn signal indicator (the right one and it's green) that flashes for either the left turn or the right turn. What you might expect to see as the left turn indicator is actually the high beam indicator and is red in color. see image below. You can see in the picture below, that the new harness has doubled up the blue wires (to make 8 wires) as per Apache... but the original harness I am replacing has only 6 wires.

My question is, how on earth does two wires going to one light bulb not backfeed the the entire circuit to make all signals flash like hazard lights AND how do I wire my truck so it's like factory? Does the signal light switch manage this or perhaps I need a resistor of some kind or what??