Electrical Problems on 2008 Chrysler PT Cruiser

All the lights on my car headlights, dash lights, reading lamps, and any other lights you can think of get very dim and then brighten up. They may also flicker. I have taken the car to 3 different dealers who say they cannot duplicate the problem and nothing is wrong with it. I went to wal-mart and bought a little voltage tester with a number readout and red yellow and a green light that plugs into the power accessory plug. The voltage readings fluctuate anywhere from 14.9 volts to 12.5 volts. The lights get dim at 12.5 volts and brighten up t 14.9 volts. Often the little red light comes on when the problem occurs. It occurs most after the car has been driven and warms up. The dealer says he put it on the midtronics tester and it shows there is no problem. I took it to a local mechanic who told me my battery was bad. I paid for a new battery and all was well for about a week and now the problem is back. Any help on this problem is appreciated.

Asked by for the 2008 Chrysler PT Cruiser
It would be a good idea to have your Alternator Load tested to make sure that is output is at it's rated capacity.The Midtronics tester will not perform this test. You need to use a Sun VAT 40 or similar tester. The voltage should not drop to 12.5 volts with the engine running. A defective alternator can produce enough voltage as indicated (14.9 volts) is normal, but if the Ampereage is below rating, it cannot keep up with the electrical demands placed upon it with all accessories running. Also make sure the belt is tight, electrical connections at the alternator are tight and the battery terminals are tight and free of corrosion. The worst case scenerio is the voltage regulator is intermittent or has failed. Charging system voltage is controlled by the Power Train Control Module (PCM).
Thank you for your response I will take your advice to a local mechanic and get him to check those things. Thanks again
1 more answer , 1 more comment
Hi aggie I Have Read your problem. I have a 1993 New Yorker and my head lights go on and off while driving. It seems it does it more when the heater is on. I flick on and off the light switch for the headm lights and it works only for alittle bit. I took it to mechanic and he replace the light switch in the car three times and did not work. Also the lights come back on when you tap on the head light switch.
I still have not found the problem to my car after many more trips to auto mechanics. I have gone through 4 batteries since then. What could be ruining the batteries? It seems nobody wants to work on my car. THey just want to get the money for checking it out. One guy wouldn't even take my money he said no mechanic likes working on pt's