Indicator lights on an older TJM Bullbar

Hi there

I'm finally hooking up the bullbar indicators on my 78-series. It's a wonder I haven't been pulled over by the police before now! Anyway, it was a second-hand bar and the lights came with it. They're nothing fancy but work. I've successfully hooked up the passenger side light, soldering the positive and earth wires onto the Troopy's indicator wires.

The driver's side light/housing only had a positive wire attached. I'm assuming an earth wire is missing? The problem I have is that I don't know how the earth wire is attached to the housing. I can't see how it's done on the passenger side housing. I've searched online, but can't find anything.

Would anyone know how and where to attach the earth wire? I can't be bothered looking for new lights for this older bar. So many new ones seem to have different dimensions and I'm happy to stick with halogen globes for the bullbar.

I've attached a photo of the housing. I tried attaching the added earth wire to the spring, but the new bulb never lit up when tested.

Regards

Paul