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Thread: Alternator died, best replacement? 1999120" LTC ECB dual alternator

  1. #16


    Quote Originally Posted by AceLimo View Post
    I just confirmed both alternators were dead (neither producing more than .5 volts or higher. That being said, I did check the wiring, it seems that both alternators are on the same circuit, meaning when the main battery is connected its showing 12 volts on both alternator red cables (without the alternator connected). So this leads me to believe the wiring for both alternators are setup to charge the main battery and supply power to the vehicle? Is this correct, and if so, is this the normal way dual alternators are supposed to be setup? If not could it be possible that the previous owner somehow rigged the switch to always be on so the 2nd alternator is always sending power to the main car?

    When the car died all the electronics died including the ones in the back and the headlights and all.
    I have been dealing with my dual alternators in one of our 300s the past month, I had our alternator for the rear cab go first which was directly wired to the rear of the car only which killed all the electrical to the back of the cab (no power) so we replaced it, we just had the main alternator test bad after an 8 hour run time but the car remained running, so I a not sure if the alternator was really bad as the car still ran (unless the the second alternator also runs as a back up alternator for the main alternator), we had the battery light come on after the car ran 18 hours straight on Saturday so we are taking it back to the mechanic this week to get it checked out, I guess the best set up would be to have your main alternator only run the car and have the second alternator run the rear cab (if possible to have the second alternator run as a back up feed for the main alternator along with running the rear cab)... Anyone have any additional info on this, this is a Royal Coach build?
    Michael Niederst
    NM Limousine, LTD dba NM Limo Co.
    21400 Lorain Road | Fairview Park, OH 44126
    P. (440) 319-8900 | F. (440) 331-8815

  2. #17


    Your alt. should be completely independent from each other when your second alt. went out put all the load on the main alt.

  3. #18

    Default dual alt setup?

    So I guess i'm a little confused on how it works. One alternator and battery is specifically for the back accessories of the car? (the stuff on control panel in the front) and one alternator and battery is specifically for the vehicle itself (the normal items before it was stretched). If that is the case, then if one alternator goes out either the car's normal accessories such as headlights and dash lights will go out, and if the other alternator goes out, the other items such as the read CD player, bar lights, etc. will go out? Is that correct?

    If so, what exactly will pushing and holding the battery button down do, will it make it so it switches, or will it combine both alternators and batteries together to work on all the electronics combined?

    I'm confused because it appears my car has dual alternators but everything was running on the main one and the 2ndary one never worked, which means that either the dual alternator setup isnt working properly or was rewired? I'm scared to put both working alternators in as I am unsure how the car will handle that much output (assuming they are not meant to be working together on the same power loop).

  4. #19
    Senior Member Fairfax Limo's Avatar
    Join Date
    Jan 2008
    Northern Virginia (Metro DC)


    Now I am no expert and not a mechanic, but this is how I understand the system to work.

    You are correct, you have one alternator charging the "factory" side battery, and one alternator charging the "coachbuilder" side battery.

    Now if you go to either of the batteries and look at the positive post, you will see that there are two large red battery cables. One is coming from the alternator and one is going to a starter solenoid that looks like the following:

    Now, when you press that red "Battery" button on your driver's electrical control panel you are basically sending an electrical signal to a relay, then that relay tells that starter solenoid to engage. The starter solenoid is where the magic happens. When that starter solenoid is engaged you are bridging both batteries together. It doesn't matter which one went bad, whichever one went bad will get help from the good battery.

    Now what that means is that if your power on the factory side went out, the battery from the coachbuilder's side will power up the factory components to get you home. If your power went out in the rear, then the battery from the factory side will power up the rear.

    Here is an explanation from my Krystal Hummer owners manual:
    Auxiliary Battery Switch:
    Engaging this switch allows for the main battery to be jump started by the Aux
    Battery System. Depress and hold the switch while turning the ignition key.
    IMPORTANT: Continue holding the Aux Battery Switch for five (5) seconds after the
    engine has started, to prevent an electrical spike from the alternator. The Aux Battery
    Switch may also be used to jump start the Aux Battery (for rear coach power) by
    pulling power from the Main Battery System.

    I believe all these dual battery/dual alternator systems work this way and you will find that solenoid in there and that's where the "bridging" takes place when you press that battery button.

    I hope this helps, but again I'm not a mechanic just a guy who's had to press the battery button a few times.
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  5. #20

    Default so.

    So to confirm then that the wiring is correct, if I install just one alternator (the main one closest to the engine block) the rear electronics the coach builder put in should not have power? This will only have power if and when I attach the 2nd alternator?

  6. #21


    Yes if the solenoid is wired correct that's how it work's.If your going to wire one in just remember the wire coming from the button or relay is a ground you get the power from the to big post's on the solenoid with resister's in line.

  7. #22


    So, if its all wired up to the main alternator, should I just disregard the 2nd battery and 2nd alternator? I mean If it was re-wired for one, and the 2nd one never worked, couldn't I fry the battery by putting on 2 alternators and wouldn't they produce together nearly 26 volts?

  8. #23


    That's hard to answer with out seeing how it's wired if everything is running off the main battery the second battery is doing nothing anyway.I would hook up the main battery and alt. back to the way it was then disconnect the second battery and see if everything is working in the back of the car if it is i am guessing they wired everything to the main battery just to sell it.If your car has a/c unit's, in the back it's not going to keep up with one battery it will just keep burning up alt.

  9. #24


    I did order a 180 amp powerline to replace the main (130 amp before), so not sure if that will supply the extra power needed in case it is going to be a single alternator system. But I guess I will unhook the 2nd battery when doing the install and testing to see if anything changes with the status.

  10. #25
    Member ROADMAX's Avatar
    Join Date
    Jul 2010
    Northern New Jersey


    I think both systems share the load as one system. The only time they will isolate from each other is when say you are parked, motor off, accessories on in the back watchin' tv and chillin' and start to drain power, you will drain power "Only" from secondary battery, There is a component in line in the called a "battery isolator" which will prevent drainage from main battery engine system, so if you completely drain the rear battery you can still start 'er up and get home.... But don't quote me ....Been out of the repair biz for 15+ years.


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