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Thread: 18 Volts from Alternator

  1. #1
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    18 Volts from Alternator

    Leaving work today, started the car, had no dashlights, plenty of warning lights. Looked at voltage gauge and metered the battery, the alternator was outputting 18V.

    Decided to risk the 42min drive home. Made it home, the battery was not happy, was spiting fluid and slight vapors exiting it. Let car sit an hour, stared it, it slowly crept back up in voltage.

    I put an AC/Delco alternator in two months ago. Will try my OEM tomorrow.

    Anyone else have a similar issue?
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  2. #2
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    I changed out my alternator wiring harness, goes to the starter and battery cables, kind of a pain to do because the harness is bolted to the right rear of the engine block underneath the HVAC not much room down there . Underneath the battery junction box there can be a loose or corroded wire(s) these lead to voltage spikes and overcharging. I think charging is controlled by the engine computer on these cars, not a separate voltage regulator like the old days. Do you have a stock rating for 2003 130A Delco in there now?

    others: chime in if I'm mistaken....

  3. #3
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    Putting 18 volts into a battery will damage it pretty quickly. If you think the battery is still good you might try checking the electrolyt level to see if the acid is still covering the plates. If it is low add some distilled water.
    2004 SB #2150 of 3214 Moonroof, Heated Seats and 6 CD Changer. Non OEM Mufflers and 32,XXX miles and counting.

  4. #4
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    Could be a bad alternator, but I'd also check all the + & - connections and the resistance of the battery cables. The cables may look OK but there might be corrosion inside that you can't see.
    When you cant make them see the light, make them feel the heat.
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  5. #5
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    I'll check wiring, electrolytes etc. Yes it is a Delco 130A.
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  6. #6
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    Sounds like the regulator to me. Nothing else would cause an overcharge like that.


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    Cobra short block / ProCharger F1-A / Cog drive upgrade / Manley valves / Brian Tooley Racing valve springs / 80# inj. / -8 fuel line / -6 return / Aeromotive 340 pumps and regulator / 2012 GT500 TR6060 six speed / twin disc clutch / Driveshaft Shop GT500 upgraded CV joint shaft / BA5000 blow thru MAF/ 4.10's / Ford Racing 31 spline set up and Girdle / Metco D.S. safety loop / Stainless Works headers, cats, and everything else out back / ClassGlass hood / Bob's hood strut mod / Hurst line lock / Metco control arms / Addco front and rear sway bars / Monroe severe duty shocks all around / Race concepts rotors / Badgeless grille / 35% tint / FBM's interior LED kit and ambient lighting kit / Pioneer FB700 deck / kenwood speaker 4 Ch. / Rockford Fosgate 10" sub and amp / Kicker 6 X 8's all around / back up cam / bluetooth / Pioneer Xm / 704 RWHP 603 RWTQ tuned by Mo's Speedshop.

  7. #7
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    Quote Originally Posted by justbob View Post
    Sounds like the regulator to me. Nothing else would cause an overcharge like that.


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    Yep, had the same issue although in a different way. DB Electrical alternator, think it was a 160A, had 5000 miles on it at the time. Was driving around the block with Blackened300a and he egged me on to do a burnout from a stop sign in a four way. Half way though the intersection the alternator imploded, took out the regulator, and the volt gauge shot past 18 volts. The car started shutting down electrical systems by the time I got it around the block back into his shop.

    Your regulator is most likely shot.


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  8. #8
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    Quote Originally Posted by offroadkarter View Post
    Yep, had the same issue although in a different way. DB Electrical alternator, think it was a 160A, had 5000 miles on it at the time. Was driving around the block with Blackened300a and he egged me on to do a burnout from a stop sign in a four way. Half way though the intersection the alternator imploded, took out the regulator, and the volt gauge shot past 18 volts. The car started shutting down electrical systems by the time I got it around the block back into his shop.

    Your regulator is most likely shot.
    LOL So Im not the only one with an issue from them?

    I had a thirteen month old starter I bought from them that caught a hell of an electrical fire inside the solenoid at a stop light! There was so much smoke so fast rolling out of every front end body gap that I nearly made a doodoo In my boxer briefs! I ran the left lane red and the second out of oncoming danger shut her down and coasted to a quick stop. Fire was increasing so I wrapped something around the negative cable and just started yanking till it came off.

    Once I located the approximate area I severed the cable by cutting it off the starter and push started it to get home. The plastic on the solenoid had melted internally enough to sag and ground out. Perhaps header heat but it was wrapped just like the original starter that surely didnt do that? I thinks cheap azz plastic in the rebuild kit they used and quite possibly the case here as well with the new Delco regular and your DB. They are obviously outsourced.


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    Cobra short block / ProCharger F1-A / Cog drive upgrade / Manley valves / Brian Tooley Racing valve springs / 80# inj. / -8 fuel line / -6 return / Aeromotive 340 pumps and regulator / 2012 GT500 TR6060 six speed / twin disc clutch / Driveshaft Shop GT500 upgraded CV joint shaft / BA5000 blow thru MAF/ 4.10's / Ford Racing 31 spline set up and Girdle / Metco D.S. safety loop / Stainless Works headers, cats, and everything else out back / ClassGlass hood / Bob's hood strut mod / Hurst line lock / Metco control arms / Addco front and rear sway bars / Monroe severe duty shocks all around / Race concepts rotors / Badgeless grille / 35% tint / FBM's interior LED kit and ambient lighting kit / Pioneer FB700 deck / kenwood speaker 4 Ch. / Rockford Fosgate 10" sub and amp / Kicker 6 X 8's all around / back up cam / bluetooth / Pioneer Xm / 704 RWHP 603 RWTQ tuned by Mo's Speedshop.

  9. #9
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    Well, since the battery was completely shot, I put a 850CCA Motorcraft battery in, things are working fine with the Delco 130A left in the car. Everything in my electronics background says the Regulator too! The alternator voltage has been maintaining normally now. I had a Battery $ource battery in there, which may have been the issue. I also have a slight flicker in the gauge lights which may be the wire harness corrosion. A replacement harness is being procured.

    I did notice in the hot FL summer, the OEM alternator was running 11V a majority of the time, and normal during cooler conditions. I thought the OEM alternator was the issue, thus installed the Delco. The lower voltage issue continued when hot. I then assumed it was a temperature issue the ECM was controlling after the alternator swap. All the BS battery was in there all along. The battery always read 12V, but perhaps there were current issues with it in the heat and thus my issues. Could a cell be shorted at times causing the alternator to up the voltage to compensate?
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  10. #10
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    Learn something new everyday I guess. Ive never heard of a bad battery overcharging. As for your loss in heat and flickering it is more than likely wiring or connections.

    My car has done it since it was a year old. Obviously it got way worse once I added dual fuel pumps, high draw radiator fan, and two audio amps/sub and anything else Im forgetting. It got to be all but not drivable unless you turned things off at stop lights. I finally did the big3 upgrade (and a 200 amp alternator) and simply WOW! My factory candle headlights are now BRIGHT!! With everything running, at night, in the summer heat.

    Yeah the bigger alternator obviously helped but I bet most of it came from the wiring upgrade considering the dancing/flickering instrumentation when it was stock the first few years with only 15-40,000 miles on her.


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    Cobra short block / ProCharger F1-A / Cog drive upgrade / Manley valves / Brian Tooley Racing valve springs / 80# inj. / -8 fuel line / -6 return / Aeromotive 340 pumps and regulator / 2012 GT500 TR6060 six speed / twin disc clutch / Driveshaft Shop GT500 upgraded CV joint shaft / BA5000 blow thru MAF/ 4.10's / Ford Racing 31 spline set up and Girdle / Metco D.S. safety loop / Stainless Works headers, cats, and everything else out back / ClassGlass hood / Bob's hood strut mod / Hurst line lock / Metco control arms / Addco front and rear sway bars / Monroe severe duty shocks all around / Race concepts rotors / Badgeless grille / 35% tint / FBM's interior LED kit and ambient lighting kit / Pioneer FB700 deck / kenwood speaker 4 Ch. / Rockford Fosgate 10" sub and amp / Kicker 6 X 8's all around / back up cam / bluetooth / Pioneer Xm / 704 RWHP 603 RWTQ tuned by Mo's Speedshop.

  11. #11
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    The saga continues...The new Motorcraft battery died also. Something I didn't think of looking for was parasitic drain. That is the culprit! The current drain is 180mA. I eliminated the starter and alternator as root cause. Disconnected the BJB (Battery Junction Box) it went to zero. So my digging starts there. Does anyone have measurements of normal drain current? I'm assuming 50mA or so. Pulled out the Service wiring book and went to work. I did find the horn circuit was pulling a lot. The relay control line was being pulled low by the LCM (Light Control Module) but not enough to activate the relay. Opened the LCM, the protection diode is working, then it goes to an IC which I cannot find datasheets on TI 71001FB/900T01. Chips are sold online, but is it a programmable IC or a standard, I cannot locate info. May just have to buy a LCM or just cut the horn wire. The wire only signals the horn for alarm or door locking, the steering control will still function.
    Last edited by pantheroc; 03-18-2020 at 07:42 PM.
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  12. #12
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    Quote Originally Posted by pantheroc View Post
    The saga continues...The new Motorcraft battery died also. Something I didn't think of looking for was parasitic drain. That is the culprit! The current drain is 180mA. I eliminated the starter and alternator as root cause. Disconnected the BJB (Battery Junction Box) it went to zero. So my digging starts there. Does anyone have measurements of normal drain current? I'm assuming 50mA or so. Pulled out the Service wiring book and went to work. I did find the horn circuit was pulling a lot. The relay control line was being pulled low by the LCM (Light Control Module) but not enough to activate the relay. Opened the LCM, the protection diode is working, then it goes to an IC which I cannot find datasheets on TI 71001FB/900T01. Chips are sold online, but is it a programmable IC or a standard, I cannot locate info. May just have to buy a LCM or just cut the horn wire. The wire only signals the horn for alarm or door locking, the steering control will still function.
    Some early S197 Mustangs had the 'parasitic draw' malaise, mine was one of them (related to how I came to possess this fine car but that's another story). Apparently many dealers don't read service bulletins like they are supposed to. On S197s, it usually boiled down to two issues. The radio (new to Mustang for 2005) wasn't turning off even though the display was blank - Ford stated to make sure to turn off the radio BEFORE turning off Mustang. The other being the Smart Module Junction Box, also new to Mustang for 2005 (fuse block behind in RH kick panel in the interior). This allows power to remain on to Mustang's accessories for up to a minute after the key is turned off - apparently some weren't turning off correctly. With all doors closed, one of the first FSBs stated to disconnect the battery, negative first, fully charge the battery, then reconnect, negative last. This resets the Smart Module Junction Box - incredibly simple solution to an issue that stumped dealer personnel and led to the original owners selling Mustang to me. Otherwise, look for the usual culprits. Yes, Ford stated a 50mA service limit while my car draws 30mA. Will start at 1.6A at the beginning of the prescribed test procedure.
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