Ok, I cannot get the drivers sidemarker to be as bright as the passenger's side. I have tried troubleshooting many things. I shall list them.

applied Oxguard to all contact points after testing positive for 12volts.

Tested other bulbs in both sides
cleaned bulb socket
tightened bulb socket

I am so lost. just when i thought i had it all figured out and went ot test it, because i was certain there couldnt be any other thing, it still doesnt work....i even put aluminum foil on the inside of the housing becasue it wasnt as shiney as the other side...still nothing... please help! it drives me nuts!
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Blue '89 Volvo 244 DL 5-speed w/ 176k

Along the same lines as below, are you sure the Bulb on the one side is the same as the bulb on the other?? What I mean is that some of the Amber bulbs are Dyed amber and some are painted amber. The painted ones are dimmer.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me

I switched the bulbs, the one that was bright (P/S) became dim when put in the D/S and visa versa
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Blue '89 Volvo 244 DL 5-speed w/ 176k

Just trying to review your POST. You tested both sockets D/S and P/S and got the same Voltage out of each? ARe you sure you are not getting 13V out of one side and 12V out of the dim one?
The only thing I can think of is that most of the strands of wire going to the D/S socket are broken so the very few strands that are left can't handle the current draw of the bulb (heat = resistance = reduction in Voltage).
Can you wiggle the Wiring coming from the Bulb while the lights are on and see if it gets brighter and dimmer? If that's not it....I'm stumped.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me

Did you try changing or exchanging bulbs? All connections good? Are you running a ground or using it as both steady on with lights on and a signal when directionals are on? Sometimes these things do try ones patience.

Good luck,

dick