I have to agree with EFLI.
It's pointless faffing around with a second hand fitting that supposedly has instructions that do not give wiring details.
For the cost involved, just replace it and have done. To boot, you get a brand new fitting with a 12 month guarantee.
It is a new one I'm trying to fit so already has got guarantee.
I would put brown to brown then red to the white like the original light but don't want to risk it.