Vw golf cab mk3.5 why have i got high beam but no low beam

Most total headlight failures are caused by a bad component like a fuse, relay, or module. Wiring problems can also cause both headlights to stop working. High beam headlights don't work or low beams don't work. If just one bulb fails to work in either high beam mode or low beam mode, it may be the bulb. Check your manual to find your headlamp relay.

If this fuse box diagram below is correct you have a fuse for left low beam head light and another fuse for right low beam head light and a third fuse for both the high beam headlights. If the fuse is good for the right I think I would take the left low beam head light and put on the right side and see if it works on the right side. If you think you got the wiring correct. It may be the bulb is bad from the wires which shorted out. A voltmeter or test light to the socket would save some time switching the lights. I have had the socket bad before and had to change the bulb socket.
https://fusesdiagram.com/ford/fuse-box-diagram-ford-taurus-2000-2007.html

It shouldn't be the high/low beam switch, as that switches the high/low beam relays. One high beam relay supplies power for both sides, one for low beam, both sides. If you were to lose switch function or a relay, you would lose the high beams or the low beams, but not for just one side. It would be interesting to probe the fuses with a test light and see if you're getting power to and through them. If you are, the problem would be between the fuse box and the headlight, if your not getting power to the left head light fuses, the problem will be in the fuse box. Good luck!

most likely a faulty turn signal switch

You have a bad switch

check the fuses first, no luck replace the day time running light module.

You know the fuse for the high beams is good ( Cab fuse panel fuse # 16 ) and the pass low beam fuse ( cab fuse panel # 26 ).
Might want to check cab fuse panel fuse #28 ( this is the driver's side low beam ).

If this fuse has power on both sides ( with the low beams on ) next you can pull the headlamps, and check for power at the connectors, but depending when the last bulb change took place, I would say you need need bulbs. ( need at least 1 for the high beam out )
Confirming with a meter at the headlamp would be a good idea, before spending the money.

The bulb connector has 3 pins.
Black wire is ground on both sides
Light Green w/ Black stripe wire is high beams on both sides
Driver Lo = Dark Blue w/ white stripe
Pass Lo = Dark Green w/ Orange stripe.

Sounds like you have a bad headlight switch. I would also check fuses 1&2 in the fuse box, those are for the low beam headlights, and fuse 3 is for the instrument panel lights and the license plate lights. All 3 should be 10 amp fuses.

thare is a high beam relay and a low beam relay in the fuse box find the low beam relay and replace it. if this dont work its probabley the switch

i would say you have a wiring fault, there's not much else in the circuit.... although it does sound like a switch fault, did you put a new or used switch in?? otherwise you may have to take it to an auto-electrician.....