Towbar Socket pins 5 & 7

[DrZhivago]

Pins 5 & 7 supply the nearside and offside side lights. Is there a story why they are separate? I guess it is just so you will still have some rear light if one of the pins or its wires fail, but the other safety-critical pins (for indicators and stops) are not duplicated.

 

[Damian]

You answered your own question.

 

[colin-yorkshire]

yep guessed right. it's a throwback from the early days of trailer lighting.
the reason the lights have two circuits is because on some tow vehicles the left or right side rear lights could be left on/off for the purpose of leaving a parking light on. think thats the case still on some cars.
if all the other circuits had dual feeds you would need a 13pin plug just for the trailer lights.

 

[DrZhivago]

You answered your own question.

throwback from the early days of trailer lighting ... on some tow vehicles the left or right side rear lights could be left on/off for the purpose of leaving a parking light on.

Makes sense, but a throwback to, AFAIR, the early 70's when lights had to be left on when parked, and Halfords etc sold a minimal two-way white/red light that clipped to the top of an offside window and was powered from the *** lighter. So that's why Pin 5 is just for the offside lights and Pin 7 for the nearside has the number plate lamp with it, as you didn't need the number plate lamp of for parking.