I had problems with the wiring in the housings but if you've swapped housing and it's not working I suspect its in the body control modules or wiring. I would check for any trouble codes on the body modules and do a hard reboot on a overnight fully charged battery. Unhook battery, charge over night, hook back up and see what comes to life. You'll need the codes to really diagnose what's going on.

There's a little Lucas in these cats. He can be tough to exorcise at times.

 

Which lights are "all the lights on the left side"? The odds are very low that more than one light bulb fails at the same time.

The first thing you may wish to check is the battery voltage after the car has been turned off for 10 mins. There are lots of threads here discussing battery voltage and how it creates somewhat inconsistant gremlins when voltage drops below 12V. Most autoparts stores will load test it for free if it is low. The last thing about batteries, if you are not using one already think about a good battery tender when the car is not going to be driven for several days.

 

For what it is worth, I had a similar problem on my 2001 XKR. Did everything you did. Bulbs, fuses, relays, etc. It had to be wiring. With engine off and light switch on, fiddled with wires in the cramped area near light. Eventually the light lit. Problem was a break inside a color coded wire to the bulb. Unbelievable. Not it is fixed and never failed again.

 

 

Boom, nailed it.