Dear Volvo specialists and enthusiasts,
I've got an issue with my 2002 Volvo V70 XC (152000 odo.). The issue is as follows:
several months ago I noticed that the lights (low beams and interior lights) go dim if I use the rear window motors, also when the heating or just the cabin fan is on and I drive I could hear how the fan RPM drops when braking. If I turned on the electric power consumers such as windshield defrost, seats heating the effects were more noticeable.
I took multimeter and measured voltage at the battery terminals in the trunk. when the engine was not running, it showed somewhere around 12.1V, After engine start the Voltage increased to 14.1 (the values after decimal point are approximate), when turning on the power consumers (all I could find in the car) the Voltage dropped to 12V. So I decided to go to the mechanic, he told me it was the faulty alternator, replaced it (remanufactured Bosch) but the problem didn't go away, it got better, but the lights still go dim. I went to autozone to test the battery, but the guy told me it was fine for the 4 yrs old one. Now the voltage readings on the running engine is 13.7 (with new alternator) but when I plug in the consumers it doesn't drop that significantly, however, it drops to 13.4-5 and the lights go dim when turning on the motors. I checked the fuses and those which are responsible for the rear window motors are 30A, so means pretty powerful. I also tried to check if the ground wires are all in a good shape (six bolts under the hood and one in the trunk, I could find only these) but it didn't help. Also, if I try to turn off the consumers the lights still go dim when I try to "close" rear windows, meaning that the I observe noticeable voltage drop even without much loading. One more thing (I'm not sure if it's related, but anyways), I've noticed that one of the relays in the under hood fuse box becomes pretty hot (120-150 F) when engine running (relay is FMA2, ECU). I also got "Low battery voltage" (before and after alternator replacement) several times, but it's pretty rear an if I turn off and back on the ignition it goes away. I'm kind of stuck here, because I'm afraid that the issue will fry the new alternator. Please, help to solve this problem!
Thank you!

 

you may have a cabling issue. any signs of bubbled insulation (indicating heat)? did you check for corrosion around the battery posts/terminals, clean them with a wire brush tool as well as the ground straps? You may need to measure the resistance from the battery terminals up to the main fuse box (see if your model has the jumper cable posts under the hood to measure from)