you can take a multimeter and in Ohm testing mode put one probe on the positive lug on the alternator and the other on the positive battery terminal. What comes back should be a really low number. If it's not very low, like close to 0 then you might have a wiring issue. While your at it you might want to try and tighten everything up. Do you have an aftermarket stereo or some kind of device pulling a bunch of extra juice? Also where are you getting your voltage measurements you are posting?

 

Only thing aftermarket wise is just 4 gauges. Everything is pretty damn tightened. I did have one loose nut for the alternator output but after it was tightened it didn't make a difference. While driving I'm getting voltage readings from lighter socket. When out of the car, I use a battery tester. It starts at 14 fine when testing from the battery. When I turn ac and all the shazz on it'll drop to low 12's and I can see the needle from the reader going down very slowly. I'll try the Ohm thing.

 

While your getting that, try running the car with everything turned on (as many different things as you can, and the car at operating temp) and take a voltage reading from the cig lighter and the positive and negative battery terminal. It's good if they are almost the same number, the further apart they are the more likely you have some non alternator electrical issue.

 

Good idea, thanks!

 

Had a mechanic take a look and noticed the wires from the alternator output is very green and corroded for how much we can see. Said it could be the wire failing.

So at this point I wonder if I should just purchase this.. Is the harness itself easy to do? Meaning I don't have to do anything extreme to be able to unplug and replug everything.
https://stmtuned.com/products/positi...t=990289362953

 

I would replace it, if you wanted to go the OEM route then that harness is a good option, I think at the least your going to have to remove the battery and tray. Depending on your setup maybe the upper intercooler piping as well. Those don't count to me as extreme though, your not pulling the engine or dropping the trans or anything. There is one trans bolt that will need to come out though. I might be jumping the gun on saying replace it, without pics its hard to determine the level of degradation. I have just seen so many fried alternator leads in my time its almost just like an instinct to upgrade/replace.

 

Alternator is bad. Tested the alternator itself with a multimeter and it was only putting out like 12ish volts. So it seems when its cool, the alternator voltage is more normal. When it starts to warm up and gets hot, the voltage drops. Good thing I went with an OEM so it could only last for a year and a half :/

 

When you say itself you mean you just put the meter directly on the alternator lug? I ask because if you disconnect the power from the alternator it wont work right, alternators need power to work. Just thought I would clarify. If it is a dead alternator then that really sucks. Even crappy aftermarkets usually last longer then that. Could be that the corroded cabling was making life hard for the alternator but still pretty unusual.

 

I replaced the wire that goes from battery to the alternator. When the test was redone, the battery was connected to the alt still, car started. Then measured from the alternator directly. And unfortunately there is no warranty on mitsubishi electrical stuff per stm.

 

Bummer, hopefully it was the cabling your replacing that killed it. Otherwise you still have an alternator killing gremlin lurking somewhere in there, or you have really bad luck. You might consider having the alternator rebuilt locally. You know support local business and probably get a decent warranty out of it. Turn around time might actually be faster then ordering one.

 

Yea all I can really do at this point is replace and if I get the same results then yes something else is bad. Going with an alternator from napa. Might as well get one that has a warranty...

 

I would go around and just inspect the rest of the harness, as much as you can anyway, and see if anything else catches your eye. The connections that connect pretty much the entire interior electrical system to the battery/alternator are here:



my car is a DD so pardon stuff being a little dirty.

So you can measure voltage drop from the alternator to this point and then from this point to pretty much anything else to help diagnose an issue. It would probably also be a good idea to inspect/tighten all (or as many as you can get to) the chassis grounds, our cars aren't exactly the smoothest and vibrations loosen stuff over time.

Here are all the chassis grounds (evo 8)

 

Thanks, I'll have to give those a look.