Recently I picked up some cheap fog lights just to get started with. I first ran them on my workbench power supply and they're actually pretty bright but I get them on my truck and they're dim.
I have wired them up like so

The original diagram is here Fog Light Wiring with Bosch Relay
The only thing I can see that may be dimming them is that I don't have them separately grounded. Any ideas?

 

If you have them properly wired to a relay, switch & power source then it's the ground. They should be grounded individually for them to work properly. When you 'bench tested' them they were bright so you know they work. Ground them & or trace the + power as well.

 

Grounding them separately did the trick. Thanks!

 

Good to hear!