Crazy Electrical Issues


New member
I have been having the oddest electrical problems ever. I don't know if it is cold relate since it has been ungodly cold for so long. It started that my cigarette lighter wouldn't give my phone charger enough juice to charge the phone until I drove between 30-60 minutes. The car wasn't starting well in the cold so I replaced the battery (didn't change a thing, didn't expect it to but I was hoping for an electrical miracle). I still had the problem. I then realized that the rear defrost and the mirror heaters also took the same amount of time to start working. I took it to Subaru and they told me nothing was wrong with it (probably because I had to drive 45 minutes to get there). A few weeks later I notice that my seat heater is giving me the same problem. Just the other day I noticed that the auto dim on the rear view mirror wasn't working. I took a wild guess and turned the seat heater off and the auto dim started working. Has anyone had any of these issues? I have worked on electronics for a long time and never have a seen an issue where the longer something was on the better it worked. Any suggestions or solutions would be welcome. I have tried having one thing at a time on and every combination of things on at the same time to see if one thing might be causing the other issues, not so much.



New member
Evergreen checked it out and said it was completely normal. That was the first thing I thought of. I am thinking of replacing it anyway.

Do you have any sort of OBD2 reader? I would say to watch your voltage when you first start it up. Once the car is running it just works as a ballast basically. If your voltage fluctuates or is low then I would say go over all the grounds you can find and recheck. If that doesn't help then its the alternator. Electrical power systems will do funky things with voltage being off.



I had exactly Bryan's thoughts reading through that. It's either your alternator or you have a bad/intermittent ground. Since the engine runs fine I'd expect the engine ground to be fine, because the ECU will ground through that circuit, but you be grounding everything else through the ECU circuit, which doesn't have big enough wires to run all your accessories. Which would explain why the fan makes other things not work.

I'd start by running the engine, turning on high loads like rear defrost and the blower, and first of all making sure you have over 13.5 volts at the battery terminals. Check the voltage between the positive battery terminal and the output of the alternator, should be less than half a volt drop. Then check all the grounding points referenced to the negative terminal of the battery.

Put the black lead on the battery negative, and use the positive lead of the meter to check voltage drops. You should have zero volts between any grounded point on the vehicle, in reality that won't happen, but you shouldn't have more than half a volt difference. So check the alternator, engine block (make sure to scrape down to shiny metal for these).

You might have to use an extra length of wire, but check at the lighter plug, that's an easy ground point in the car's electrical system.

I used that to track an issue on my car once, I had 4 volts between the battery and the lighter ground... And it changed based on what loads I ran. That helped me narrow down where the grounding issue was.


Nigel Prodrive

Dirt surfer
Have you noticed if the speedo and tach are acting weird?  Irregular voltage from the alt will often show up in wonky instrument action.

New alt = prob gone, is my bet.

Well worth sussing first as Chris suggests above, tho. throwing $$ at new parts "hoping for electrical miracle" isn't the most effective use of said $$. ;^P


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