Mike Alabama Posted October 15, 2019 Share Posted October 15, 2019 Need help! Cant seem to find the exact same issue on here like I am having. 2002 Forester 5 speed installed new alternator checked all brakes. Battery and brake light are on and will go OFF, when I unplug the 2 wire alternator connector both of the lights will go off, while the brake light is on also it gets brighter when I actually pull the brake up so don't think it is that switch. What I have determined and tried so far: 1. Battery at rest 12.6 V and i also checked with an electronic load tester and it shows 100% charged, <4 meg ohms resistance and passed a 625CCA load test. 2. With car running battery reads 14.8 to 15V (already replaced alternator already assuming it was a bad regulator and it had 180K miles on it before doing any of this) 3. When I unplug the 2 wire connector on the alternator both lights go out and the battery goes to about 12.3V running with no accessories on. 4. I have cleaned body and motor ground connections with sandpaper and reinstalled. Cleaned and put protector on battery post. Used electrical cleaner on the 2 wire Alt connector. I don't understand the problem, is this and the other alternator possibly putting out over voltage out of cars computer accepted parameter and causing the light(s) to come on? Am I missing something? I am a master electrician (big wires LOL) and used to restore old cars and do modern engine transplants into them so not a total novice but this LITTLE problem on the Rue has me scratching my head....Any suggestions? Link to comment Share on other sites More sharing options...
idosubaru Posted October 16, 2019 Share Posted October 16, 2019 (edited) *** Are the old and new alternator symptoms identical, different, or don’t know? If identical, then #3 below is more likely. 1. Clean up, tighten, and verify battery terminal connections and wiring. Check voltage at alternator and battery and make sure they’re the same. 2. Aftermarket alternators aren’t high percentage. zero zero zero surprise if the alt is garbage. 3. Check for crank pulley separation. If it’s bad you can see it. Or draw a line across the face of the crank pulley. Run the engine. If the line “breaks” your crank pulley is separated and you need a new one. You can tack weld it or use through bolts to hold it together temporarily or permanently. Edited October 16, 2019 by idosubaru 1 Link to comment Share on other sites More sharing options...
Mike Alabama Posted October 16, 2019 Author Share Posted October 16, 2019 (edited) *** unfortunately I did not check the old one other than ir was putting out a little over 15v also so I assumed it was overcharging 1.A done and all are OK 1.B will check that 2. Understand but I did buy a Remy in the HOPES that would not happen 3. Not quite understanding 3 but I will look and see tomorrow, I have 5 Ford diesels now (WVO runner) so those cast harmonic monsters don't have issues. I assume Subaru is some sort of multi piece? All other accessories including AC and PS is working good and no noises. THANKS for your reply!! Edited October 16, 2019 by Mike Alabama Forgot to thank Link to comment Share on other sites More sharing options...
nvu Posted October 16, 2019 Share Posted October 16, 2019 Check and clean the 2pin connector carefully. Replace if needed. That connector is the sense circuit, one wire runs as directly to the battery as possible, the other goes through fuses, dash circuit, through the dash battery lamp. Oldschool subarus have a light bulb for the battery for resistance and the charging circuit depends on that. The alternator uses the voltage differential between two wires to regulate power. If the connector is dirty or wires are corroded, the extra resistance will force more voltage. Yeah and unplugging it completely disables the charging so the lights turn off. No computer involved. The light turns on if there's a big enough voltage differential. No idea how newer ones work, they have leds and digital gauges. 1 Link to comment Share on other sites More sharing options...
Mike Alabama Posted October 16, 2019 Author Share Posted October 16, 2019 Do you know the max voltage before the ECM turns the battery light on? I was a bit embarrassed to post and I thought an 02 was old :) It does help that I know essentially where the 2 wires go to look for a problem at the origination. Will look deeper tomorrow. Thanks for the reply Link to comment Share on other sites More sharing options...
Rampage Posted October 16, 2019 Share Posted October 16, 2019 Earlier cars charged at 13.8 V. Some of the newer ones are around 14.4 V. I have a Remy alternator right now that I have to return because it put out too much voltage. It melted the plastic on the coil for the clutch on the A/C Compressor among other things. After I saw that plastic slung all over the place, I did not want to start it just to see what the voltage really was. Subaru's price for the A/C Compressor on our 95 RHD Legacy Wagon is around $1000.00. I looked at a WRX two years ago for a friend that was blowing an 80 AMP fuse. The alternator was putting out over 20 Volts and it was the original that came on the car. 1 Link to comment Share on other sites More sharing options...
nvu Posted October 16, 2019 Share Posted October 16, 2019 The computer has no control over the battery light. From the 2pin connector, one wire goes to the battery lamp -> fusebox -> positive rail. The other wire goes battery positive as directly as possible. If the voltage the alternator puts out is too high or too low compared to the positive rail at the fuse block , the light comes on from differential voltage. One wire should have some resistance to the positive battery. The other should have very little resistance. 1 Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted October 17, 2019 Share Posted October 17, 2019 some odd things can happen from 2 sources; frayed/shorted wires in the body-to-hatch rubber boot. and brake light bulbs or corrosion in the bulb sockets. 2 Link to comment Share on other sites More sharing options...
idosubaru Posted October 17, 2019 Share Posted October 17, 2019 15volts - that’s too high isn’t it? electrical isn’t my strong point but I’d be asking that first - is that too much or okay? LuckyTexan has a great point - if the light is the only issue then check all the bulbs and socket connections for corossion in the rear. That light can fade in and out based on poor bulb connectivity. Link to comment Share on other sites More sharing options...
Rampage Posted October 17, 2019 Share Posted October 17, 2019 17 minutes ago, idosubaru said: 15volts - that’s too high isn’t it? Yes, it is too high. A 12 volt lead acid battery should be charged at 14 volts. Any higher and it will eat away the lead plates and boils away the acid. That higher charge voltage is the main reason you see so many newer vehicles with burned out headlights and parking lights. The older cars like our 95 charge at 13.8 volts. I very seldom have a burned out bulb. I think two parking lights in the last ten years. Never a headlight. Usually it is just a corroded connection from moisture and age or heat. 1 Link to comment Share on other sites More sharing options...
Mike Alabama Posted October 18, 2019 Author Share Posted October 18, 2019 The rear electrical is a concept I have not considered being a factor and I thought 15V was too high for an auto but PV often charges at those voltages so I was not sure in this case, thanks for the suggestions. I have had to work late the past few days and have not been able to look into all the good suggestions but I wanted to sign in and let you all know I am here and reading them. I will work on it again Friday night or this weekend. AGAIN THANKS TO ALL!!! and I will let you know the outcome. Link to comment Share on other sites More sharing options...
Mike Alabama Posted January 2, 2020 Author Share Posted January 2, 2020 I am back! Sorry for the long delay family health issue that worked out fine and then holidays etc., so now that I am done with all my excuses! In full disclosure the car I was working on (my 2ed Forester) was a new to me used Forester and thanks to all of you and after me dumbly spending $$$ on an alternator before joining this board and you all among other things to try telling me about the fuse to control the charging was nothing I had seen on a car before and was new to me so in going through the steps all of you had suggested when I got to the fuse, wala! The dang thing was missing! Put a fuse back in and brake light went off, trouble codes (all but rear O2 sensor) went away when the voltage stabilized at a perfect level. THANKS THANKS THANKS now on to a lift kit, fix an oil leak and setting it up to flat tow behind my motor home as intended; yes manual transmission. 1 Link to comment Share on other sites More sharing options...
lmdew Posted January 2, 2020 Share Posted January 2, 2020 Glad you got it. Happy New Year! Link to comment Share on other sites More sharing options...
Recommended Posts
Please sign in to comment
You will be able to leave a comment after signing in
Sign In Now