Headlight problem.

So here goes…

I have a 1981 Golf mk1 GL. i got the car as a gift from my late grandfather. I was thinking of doing a custom build like a alotta people but after owning it for a short while, I kinda fell in love with it as is.

I'm trying to keep the car as stock as possible in terms of mechanics so I'm just trying to fix everything to stock trim except the motor. That's another story on its own.

Basically, when I drive at night only one headlight switches on on normal dip however, when I switch my Hi-beams on both lights illuminate. Can you guys help me with any fixes to this please. Do I have to replace the healight or the wiring ? Any help is appreciated.

P.S I'll try to add images by tomorrow.

Thanks in advance.

First thing to do is to Verify that if you jump 12V B+ to each of the colored wires on the left or right which ever one is not lighting up to verify that the Bulb is good or bad.

The Brown wire is ground, to the bulb so that is good because the High works….

These bulbs have 2 filaments a high and a low.
Just because the high works doesn't mean there is a major issue.  If the Bulb low beam usually the wire on the top woks with 12V then your issue is the fuse.

There are 4 fuses for the lights, 2 for the low and 2 for the high.

So that is it, the fuse or the bulb.  
I suppose the easiest is to turn the head lights on and with a DVOM to ground see if the bulb has 12V on the two non-brown wires… One will be low, and one will be high.

no 12v bad fuse
yes to 12v on both bad bulb

swap the bulbs round to see if its just blown, if not then check the fuses