Low beam only working when high beam are turned on.

[Darkness1990]

hi, so I've check forums seems to be pretty common problem but no solutions so thought I would mention, I just changed the alternator once job was done I noticed my low beams don't work but they work when I put high beams on. I've checked fuses, relays, bulbs, switch is engaging when I flick it on and off. I should also mention I have a multimeter but no idea what to check for or where to check. Checked wiring. Im lost as what to do next.... Please help!

 

[Trevor loves holden.]

Sounds like a earth problem from the light harness. They activate using earth so my guess the high beam is giving it the earth it needs.
Oh you do realise they have a high low so maybe the low filament is broken.

 

[Trevor loves holden.]

Did you switch the relay with another the same.

 

[Immortality]

I had a similar problem. It started with a broken and damaged wire in the headlight, all fuses and relays were good. Still after fixing the wires my fog lights would come on (faintly) with the headlights and one headlight was a bit dull. Turns out one of the fuses was blown (probably occurred when repairing the broken wires).

Another issue may be the high beam switch as the low beam is switched off when the high beam is turned on.

Trev, the VY headlights are different to your VS. VT onward uses separate bulbs for the head light and high beams which is a bit different to your H4 bulbs.

 

[axemurderer101]

My bet is the globes are just blown, low beam is a h4 which is a high and low beam in one globe which is why it lights up when you flick to high beam. Sometimes when they are blown the filaments can still look ok, post a close up pic on here if you are unsure.

You could also try swapping the low beam relay with the horn relay to see if its a faulty relay.