I have an issue with a 2000 Mercury Cougar. When the motor is running and the lights are turned on, the dash lights flicker and the headlights will polsate, that also includes any lights including the interior and parking lights. Recently the car has had a new battery and alternator. I sent it back in for them to check the regulator and to double check the alternator, so they said they changed it out, but the problem still exists. I then began to think it maybe a ground problem, so I added an extra ground to the motor and to the body, but still have the problem. The car is in stock form as per factory. I figured the pulsating was coming from the alternator and that the regular was faulty, all my tests done in reference to voltage output have come within range. Does anyone have anymore ideas?

 

set the multimeter to AC and see of you have any voltage that way. If you have AC voltage, the alternator/voltage regulator may still have issues. Also, if the new battery has a weak cell, it may cause this as well. If the new battery is not actually large enough (amps wise) you may get this issue. The ONLY time I''ve ever seen this was on my 94 Topaz (first car I had) and it was because the battery was DEAD and I had just jumped the car off. You should also make sure that the connections from the alternator to the battery are actually making good contact. This can also cause issues of the strange variety. And check that the battery terminals/clamps are clean and tight.

 

I did the AC voltage test, but had no reading. When I disconnected the positive terminal from the battery while the car was running and the headlights were on, the pulsating of the lights was twice as bad.The voltage at the terminals was 14.3 to 14.5volts while at idle.

 

you may need to go to autozone and let them test your alternator and battery. the battery should say 12.6 when the car isn''t running. try turning the lights on with the car not running and see what the battery says. If it drops to about 10.5 with load on it... then it''s got a weak cell. That will probably be enough to start the car still, but will cause these problems.

 

I appreciate your advice. But I have done the test with the lights off and with them on. The reading was 12.77 with them off and 12.17 with them on. I am still suspicious of the alternator myself, even though the shop had said they put another one in and had the same problem.As you know when troubleshooting you have to ignore other peoples work and start from basics. This is the history of this car, every time I have had it diagnosed it has been wrong and to make it real frustrating when they can''t find the problem they don''t want to know about it. This is why I am so frustrated with a lot of businesses these days, THEY DON"T KNOW HOW TO TROUBLESHOOT. Then the job falls back on me, if I am going to pay some shop $80 per hour, you better have more experience then what I am given.

 

yeah... really starting to sound like a voltage regulator that hasn''t failed, but is weak... or an alternator with one bad diode. I''d definitely get that alternator and regulator tested.

 

well here is the lastest. I had the car re-tested with a friend who is an old school tech. He agreed there is a problem with the regulator. Just as you also suspect, it works but not to full capacity. Plus the alternator was notreplaced with a Motorcraft but a cheap rebuild. Well say no more. So the Cougar is going back into the shop under warranty but getting replaced with a Motorcraft.Well thanks again and have a great day or as us Aussies say, Ave a good weekend and don''t forget the Mortein( that''s fly spray)

 

We like to say in the U.S.,"have a good one and don''t forget to get OFF" (that''s mosquito spray!) LOL!!!! Good luck with the car and come back and visit us. Good diagnosis Sly.

 

thanks... I try... sometimes I get it right.