i have an 06 cummins. i get in my truck after work the other night and crank it and let it run for several minutes as normal. its about 43 degrees outside. i have the door open and the interior lights all of a sudden dim down and brighten back up. then they do it again and i look at the voltage gauge and it drops from 16 or so to around 9 then picks back up. after a few minutes of idling it stops doing this and runs as normal. i go get the batteries checked and they show weak so i buy 2 optima red tops. this didn't fix the problem though. i am not sure if the ecu is going out or if the alternator is going bad or what. it charges fine after those first few minutes when it acts crazy and it only does this when its below 50 outside. any help is much appreciated. thank you.

 

its normal...its the grid heaters cycling

 

ok. is there any way to make it not do this cuz it kinda freaks me out lol! will plugging it up help?

 

pluging the block heater in will help a little, but there is nothing to worrie about, what its doing wont hurt a thing

 

ok thanks!!! i will give it a shot

 

mine did this tonight and it had me worried i had an electrical problem.

went to start the truck today, and nothing. took the batteries out and the autozone said they had zero charge....so i bought two new batteries and brought the truck back for them to test the alt. they did a test when i started the truck and it said failed, but after a minute or so of letting the truck run it said pass.

kind or worried me, i did not know if that had to do with the batteries dying or the lights dimming, just a lot going on at once and you are hypersensitive to any little thing, after something goes wrong.

 

definitely normal i dealt with this every day in alaska