One fog light brighter than other... Put in new 9145's (didn't help)?

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Prolly need to align the light bulb

 

Perhaps a wire connector has some resistance due to rust or a poor connection.

 

It could be the relay, if the contact points are corroded or making poor contact- I just don't see that your fogs would be on independent relays.

It could be a poor connection, either + or -.

 

Can you move the harness enough to plug one harness end to the other lamp and see if the brghtness changes? You mentioned using a generic harness, often that means too small of wire (resistance).

 

Try the swapping of the harness first to see if that makes a difference. You would need a very precise meter (very, very expensive) to read a difference in resistance in that short length of wire.

I just had another thought. Compare both lamp housings to see if they are the same manufacturer. You mentioned you bought them used. Perhaps one is OEM Toyota and the other is a replacement.

 

Check for corrosion (As you mentioned you did) but include all connections, as well as the ground itself. Swap left bulb with right bulb. If the dimness stays where it was, you HAVE to have a poor connection or corrosion somewhere on that circuit.

 

I had an intermittent problem with one of mine & it turned out to be the connector. I unplugged it & bent the metal tab on the inside so it would make better contact & haven't had a problem since.

 

Just a thought ...
If It's possible to measure the voltage at both bulbs/connections when they are on?? Tthey should be the same. If not you have a voltage drop (i.e. resistance) on the lower voltage line. If So, continue to measure the voltage (with the bulb on) farther back on the circuit (i.e. each prior connector, the relay , etc.) until they do measure the same. The problem will be between the last good/bad point measured. This way you only need a fairly cheapie volt meter.

Hope this helps ...