After you've searched and found what caused the problem on other people's cars, go and examine yours and see if the same condition exists - or - if your wallet is overloaded - just replace the same parts they replaced and hope it solves your problem too.
To be honest - I wouldn't even have turned to the internet for help on this - it has to be either the bulbs or a bad connection somewhere near the back of the car - I understand that not everyone has the same level of experience, some need guidance, but the idea here should be to FIND the problem and FIX it, not swap parts until it goes away.
93 - 1.3 Suzuki Swift GLX
98 - 1.8 Mitsubishi Pajero iO
98 - 2.0 Suzuki Grand Vitara