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Thread: Ballast resistor

  1. #1
    Im having troubles getting my alternator to charge. I replaced the one that was in it with a new delco #7127, still nothing. The gauge reads about 10 volts, and then when I give it a rev, the voltage drops. I replaced the gauge, same result. I have compared my wiring with the diagram off of and they are almost identical. The one difference is that I removed my ballast resistor(when I removed my points distributor for an HEI)IS this my problem? Also, the Motorola unit that came off the boat was a two wire unit, the new one is a three wire. I read that the third wire can be used for an idiot light, is this correct? Someone please help!

  2. #2
    if your using an a/c delco alternator there are two wires and a ground post i belive. we never run a regulator just an amp gauge, volt gauges are diffrent and can give u false readings through out theirs lives, best case is to install an amp gauge and run it that way, it will always let you know if its charging or not. good luck

  3. #3
    Senior Member
    Join Date
    Feb 2009
    Brendella, the ballast resistor plays no role in the charging system. Here are some things to check. You will need a Volt/Ohm meter.
    1.)Measure battery voltage AT battery with key off/engine off.
    2.)Measure voltage between alt output terminal and BATTERY negative term with key off/engine off. Should be virtually the same as reading in step 1. If reading is 0 volts you have an open circuit between alt and battery. If OK proceed to step #3
    3.) With key ON and engine OFF, measure voltage in the signal wire to alternator(with wire disconnected). It should show approx bat voltage, but only with ignition on. If no voltage present, it is possible that you disconnected it when you removed the ballast resistor. Recheck the wiring connections.
    If both of the above tests pass, then
    a.) Motorola alt was bad and the new one is wired wrong, or
    b.) Motorola alt was good and gauge wiring is faulty.
    If the alternator is not charging, you should find the problem in circuits tested above, or in the alt itself. If the alt is charging properly and you have 13+ volts at BATTERY, but gauge still shows only 10 volts then you have a problem in guage or wiring to the gauge.
    Now for some questions. Was boat originally equipped with an ampmeter? Does wiring harness have a junction block at the engine? Which terminal of the alternator did you connect the small signal wire to? (It wont work with just one wire connected to the plug-in terminals.)If you have a junction block, does it have a circuit breaker?
    Run the tests above and let us know what you find. Good luck.
    [ October 06, 2002, 03:20 PM: Message edited by: OLDSQUIRT ]

  4. #4
    Old squirt, thanks for the detail! I checked the 3 things you mentioned, all produced the same reading of 12v. I have tried 3 alternators now, all of which tested good at Pep Boys. To answer your questions, I dont think the boat ever had an ampmeter, but I do have one.the wiring harness does have a junction block at the rear. All connections have been redone. The small signal wire is connected to the terminal closest to the Batt. hook up. It is only one wire. There is no circuit breaker that I am aware of. Sounds like the one wire at the plug in terminals needs some attention, could you explain where I am supposed to route the other wire? Thanks for your help!

  5. #5
    Senior Member
    Join Date
    Feb 2009
    This is how I have always had my Delco alternator wired. Same setup, two different boats, 20 years. Look at the alternator from behind and with the connector facing straight up. The existing wire from ignition switch goes to the right hand terminal. You need to run a separate wire from the left hand terminal to the output terminal of the alternator.
    Make sure when you test the alternator, you measure voltage at battery with a meter and then compare that to what your dash mounted gauge reads.
    I wouldn't suggest converting to an ampmeter. It adds so much extra wire between the alternator and battery that it can reduce charging efficiency due to voltage drop.

  6. #6
    Okay, that must be what was meant by the drawing on the diagram. Ill try it out. Hope that works. Thanks again for your help. I'll let you know what happens.

  7. #7
    Well, im not too sure what the neghbors think of me right now, but my alternator is charging! Yeeeeeeeeeeaaaaaa haaaaaaaaahh. Thanks old squirt. Im sending 5 stars your way for all the help.

  8. #8
    Bow Tie Omega
    Oldsquirt, you also get 5 stars from me. I have heard my little brother bitch and moan all weekend. You saved him 2 bills and our trip to Laughlin this weekend. Anyone that can save a trip is worth 5 stars...Joe

  9. #9
    Senior Member
    Join Date
    Feb 2009
    More than happy to be of help. By the way , if you want to tidy the connection up a bit, the OE style alternator connector is available at most autoparts stores. Check the "HELP" line of parts. Thanks for the stars.
    So which boat is faster? The Brendella, the Omega or dads v-drive? Just thought I'd get a little family squabble started

  10. #10
    Bow Tie Omega
    I have already given in on the speed thing, my boat is a day cruiser, 21 + feet long. I will let those two speed it out. But come next spring, my boat WILL BE THE NICEST of the three.....Joe...65 mph is fast enough for me

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