Register now to get rid of these ads!

Hot Rods school me on charge light wiring

Discussion in 'The Hokey Ass Message Board' started by cluxford, Nov 12, 2021.

  1. cluxford
    Joined: Jun 5, 2012
    Posts: 53

    cluxford
    Member
    from Australia

    61 Buick.

    Was 3 wire alt...now 1 wire (I know I should have bought a 3 wire but the 1 wire came with the new front runner system, and I'm not changing it now as everything is in)

    I have a Ron francis low voltage sensor that can be wired into the dash charging idiot light.

    The RF kit says red to sign switch +...black to ground and blue to dash light. Then dash light to ground.

    I hate electrics I get so confused.

    So I assume that what happens is the sensor acts like an always off relay. When voltage drops below 11 volts it "flips" to on and puts positive voltage to the dash light.

    So what I don't understand is. In the old 3 wire alt way, the charge light would come on when there was no charge from the alt, essentially NO 12v source. But. does that mean the alt acted as a ground when no charge but broke the ground connection when there was a charge? So does that mean there was 12V coning out of the dash light not 12v going into it and that it only grounded when the alt wasn't charging.

    If my thinking above is correct then I can't just connect the RF blue wire to the dash light wire as there is no current ground connection to the dash light?

    Am I thinking this through right or am I completely confused?
     
  2. Hollywood-East
    Joined: Mar 13, 2008
    Posts: 1,606

    Hollywood-East
    Member

    The idiot light should get positive when key is on, in the conventional..
    I don't trust one wire...
     
    gimpyshotrods likes this.
  3. cluxford
    Joined: Jun 5, 2012
    Posts: 53

    cluxford
    Member
    from Australia

    thanks so how does it get ground? and it obviously goes off when in start/run so what kills that circuit
     
  4. Hollywood-East
    Joined: Mar 13, 2008
    Posts: 1,606

    Hollywood-East
    Member

    When the rpm gets around 1500 normally it shuts off
     

  5. 24riverview
    Joined: Jan 13, 2008
    Posts: 954

    24riverview
    Member

    May be what you were saying but the charge light is off when it has a 12v source from both wires, the small red wire from regulator (original) and 12v from the ignition switch thus no ground. When the alternator quits charging it does provide the ground, light comes on.

    Yes, you're correct about that. Assuming you're using the stock harness probably simplest solution would be to attach red wire at charge indicator light to a single wire grounded base socket, same as what the dash lights use.
     
    Last edited: Nov 12, 2021
  6. Hollywood-East
    Joined: Mar 13, 2008
    Posts: 1,606

    Hollywood-East
    Member

    The idiot light is reading ground from the wire coming from alt., When key is on/run, keyed power +, to light, wire from alt. Is ground till 1500 rpm, then charging light should be out
     
    Last edited: Nov 12, 2021
  7. 51504bat
    Joined: May 22, 2010
    Posts: 3,175

    51504bat
    ALLIANCE MEMBER

    Not sure about your exact set up but you may need a 2 wire socket with an isolated ground. The hot lead comes from the ignition switch and the isolated ground wire goes to the alternator. When the alternator isn't charging (with the key on) the light gets its ground via the alternator. When the alternator begins to charge it breaks the ground and the light goes off. This is one example but they can be sourced from other suppliers.

    17735_235917.jpg
     
  8. cluxford
    Joined: Jun 5, 2012
    Posts: 53

    cluxford
    Member
    from Australia

    LOL thanks so much for the responses above...I think I'm more confused :)

    Here's my original wiring diagram it's a generator not alternator. But dash connections are all still stock

    I think I need to figure out where the charge light from the old 3 wire went and figure out if that is positive or negative. All I know is right now the "GEN" light (charge light - connection J in the diagram below) does not work at any time. I want to get it to work using the RF kit. I don't want to go a 3 wire as painful as switching that all out might be as I changed all the wiring including shedding all the old wires for a 1 wire (lesson learnt there).

    I just can't see how I can get ground to the dash light if the RF kit is proving + only

    I drew a red line on the path from generator to dash light wiring.png
     
    tommyd likes this.
  9. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,581

    Johnny Gee
    Member
    from Downey, Ca

  10. You're close.... The sensor is a normally-closed relay that has a minimum pull-in/hold voltage. When the voltage is below it's minimum, it doesn't operate. Once proper voltage is reached, the relay operates and opens the normally-closed contacts and the light goes out. So yes, you'll need to disconnect the switched 12V connection to the idiot light and ground it for the light to work. It will now get its voltage from the relay.

    The idiot light on a three-wire alternator (or generator) works differently. It works on the 'difference of potential' method. You basically have two voltage sources; 12V battery voltage from the switched source, and a variable source from the alternator, or more properly, the regulator. When the alternator is working correctly, it also outputs 12V and because the light is being fed the same 12V from both directions, it doesn't light up. But if the alternator has issues and it's output falls below battery voltage, the switched power will flow through the light to try to bring the other side up to the same voltage. This current/voltage flow is what lights up the light. How big the difference is determines how bright the light gets.

    This is another reason I don't like one-wire alternators. With that sensor, it's a all-or-nothing deal. If battery voltage is 12V (rather than the 13.4 charging voltage you probably should have), until the relay sees less than it's trigger point you won't know you have a problem. On a three-wire system with the idiot light hooked up right, it will likely glow dimly, giving you more warning. I'd recommend skipping the idiot light and install a voltmeter. Or switch back to a three-wire alternator...
     
    Last edited: Nov 12, 2021
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 50,301

    squirrel
    Member

    I like Steve's explanation.

    But I disagree that the idiot light is a bad idea. Go ahead and try it, see how it works. Most of the time, you can ignore the alternator. When it dies, you do need to know, so some type of low voltage indicator would do what you need.

    btw I recently had a problem with the alternator in a slightly OT car that came with an ammeter....I didn't notice that the alternator had died, for a while, because I wasn't staring at the gauge when it quit. It took a while to notice. Fortunately I was still in a town that had a parts store with a replacement alternator, when I did finally notice it.

    Idiot lights get your attention. That is a good thing.
     
    Johnny Gee likes this.
  12. 24riverview
    Joined: Jan 13, 2008
    Posts: 954

    24riverview
    Member

    If you really want the original light to work...
    Looking at the diagram I'm assuming you have a printed circuit with twist in sockets on the backside of cluster, that will make it tougher. You can connect the blue wire from the RF kit to the small red wire at the original regulator but you'll need to modify the printed circuit to eliminate the ignition feed to the light which may be tough if it's not the last one fed by that circuit. It should be possible to trace the printed circuit to determine which side is the red wire then figure out a way to get other side out from under the socket? May have to cut the printed circuit (between "wire" paths) to get enough slack to get socket to snap in under the printed circuit on ignition feed side, if I'm making any sense. With socket twisted in on top of the red wire side and under the Ignition side it should work properly. I'm assuming the dash housing is metal, if not you'll need to figure a way to ground the non red wire side.
     
    tommyd and squirrel like this.
  13. cluxford
    Joined: Jun 5, 2012
    Posts: 53

    cluxford
    Member
    from Australia

    Thanks Steve that is a fantastic explanation. Thank you. It’s helped me a lot

    24Riv yep that’s exactly how it works. Funnily enough I have a second hand replacement printed circuit board on its way here as we speak as mine has died in the water temp lights. After weeks of testing I’ve found the printed circuit board as the issue. So I may be able to make this modification at the same time. I may even just mod it for a simple LED
     
  14. 55willys
    Joined: Dec 7, 2012
    Posts: 1,672

    55willys
    Member


    Very good description of how the idiot light circuit works. Basically when your alternator is not charging then the idiot light finds a ground through the alternator/regulator. When the alternator puts out, it also is putting out to the other side of the light and with positive on both sides there is no ground and therefore no light. Most one wire alternators are the GM 10SI that has had a jumper wire added from the positive terminal to the sense wire terminal. The sense wire is designed to give the alternator's internal regulator a reading of the fuse box voltage so that it can adjust the voltage output to compensate for any voltage drop.

    The three wires on a 10SI alternator are idiot light/exciter wire, sense wire, and main battery feed. The idiot light wire also triggers the alternator to charge at low RPM. Without the excitement from the idiot light wire you have to rely on the alternator to self excite from RPM and its own magnetic field. It seems that by going the simple route one wire alternator you have made it more complicated. One wire alternators are not the most reliable option and don't do any favors for your electrical system.

    You can have dim headlights from the alternator sensing from itself instead of where the headlight power is actually coming from. The voltage drop causes higher amperage draw creating heat in the switches and wires. Heat causes higher resitance which in turn causes higher amperage. This problem is even more pronounced when you install halogen headlights. I just replaced the headlight wiring in a car because of this very reason. I also use relays for the headlights and trigger them with the dimmer switch. I mount them close to the alternator and power them from the alternator. This will give you bright lights, less voltage drop, less stress on the wiring and switches.
     
    chevyfordman likes this.
  15. tommyd
    Joined: Dec 10, 2010
    Posts: 11,481

    tommyd
    Member
    from South Indy

    Great thread!
     
  16. Jim, the problem here is the light isn't monitoring the alternator, it's monitoring the system voltage. The light won't come on until battery voltage drops below 11 volts. By the time that happens, you're dead in the water. Now, if the trigger voltage was about 12.5V, you'd have a bit more warning. Worse case, say you have a partially failed alternator that manages to produce just enough voltage to prevent triggering the relay. You drive blissfully ignorant away for a distance, meanwhile sucking all the current capability out of the battery. When the current reserves drop below what's needed to operate the car, it quits.... and then the light comes on...

    Like I said, I don't like one-wire alternators... and that relay is a faux fix; about as useful as a security blanket or your favorite teddy bear...

    This sort of thing is why I have little faith in the aftermarket harness suppliers. Ron Francis is supposed to be one of the better ones...
     
    Last edited: Nov 13, 2021
  17. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,198

    Mr48chev
    Member

    You have to change the one wire regulator in the alternator to a standard three wire regulator.
    One wire alternators were originally designed for conversions on Farm tractors that have magneto ignition and no ignition circuit for an exciter wire. I saw them on farm equipment years before street rodders decided that having one meant that they didn't have to hide two wires.

    3 wire setup with a light
    [​IMG]

    If you are replacing a 10DN (external regulator alternator with a 10 or 12 SI this diagram makes it easier.
    [​IMG]
     
    BJR likes this.
  18. squirrel
    Joined: Sep 23, 2004
    Posts: 50,301

    squirrel
    Member

    I didn't really notice the thing about 11v when I read through it the first time...you're right, it needs to be set to a reasonable voltage, to be any use. Probably 13.0 v would be adequate to let you know that it's discharging.
     
  19. And even then it may be iffy. 'Charging voltage' can vary quite a bit due to battery charge/condition, ambient temps, connected load, and engine speed. Too low and you don't get a warning in time, too high and the light may blink at you a lot when there's nothing wrong.
     
    BJR likes this.
  20. cluxford
    Joined: Jun 5, 2012
    Posts: 53

    cluxford
    Member
    from Australia

    I’ve learned so much. Thank you all. Never had a 1 wire alt before. It came with the system. Clearly I need to just bite the bullet and change that. I’m on it
     
    BJR likes this.
  21. Or just forget the idiot light and install a voltmeter. That'll allow you to monitor the system and if there's a problem you'll see it on the gauge. A gauge will tell you more than any light...
     
  22. squirrel
    Joined: Sep 23, 2004
    Posts: 50,301

    squirrel
    Member

    Or just forget the idiot light, and the voltmeter, and drive the thing. I've noticed lately that as long as I put a rebuilt alternator in a car, and make sure it's working, it will give years of trouble free service. The only ones I've had issues with have been old worn out junk that has a bunch of miles on it.

    But I do replace batteries when they get to be 5 years old, even if they still appear to be working ok.
     
    TA DAD, Guy Patterson and BJR like this.
  23. The other advantage of a volt gauge is if the alternator is over charging.
    On my one wire the internal regulator failed causing the gauge to read 17 volts.
    I replaced the regulator, all is well.
    The various warning light configurations do not report this condition.
     
    Last edited: Nov 13, 2021
    Guy Patterson likes this.
  24. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,460

    David Gersic
    Member
    from DeKalb, IL

    I agree with the “drive it”, but not with forgetting the volt meter. Mine has saved me twice so far.

    First time was Power Tour, driving through eastern Alabama in to western Georgia. Had a chrome one-wire that had come with the car. Volt meter suddenly showing about 8V at highway cruising speed. Dropped to neutral and revved the engine, got a brief 10V and then back to 8V. Got off the highway at the first exit, found a parts store, and bought a replacement alternator. Three wire. Installed in the parking lot, connected up the harness wires that were already there for it, and drove off with a happy 14V showing for on the meter.

    An hour down the road, the volt meter dropped again, as the new reman alternator failed. Pulled off at the first exit, found another parts store, and bought another alternator. Confirmed that the other one had indeed failed, too. And parking lot swapped in its replacement before driving off with a happy 14V on the meter again.

    The second time was somewhere in the middle of Pennsylvania. Returning home from a road trip to New Jersey, cruising along at ~80MPH on 80/76 west, when the volt meter dropped from its normal happy 14V. Pulled off at the first exit, found a parts store, and opened the hood to find the remains of the alternator belt laying in the front crossmember. Went inside, counter girl starts with “year make and model…”, which got short circuited with “1937 Chevy Master Deluxe, but I don’t think that’s gonna help”. Handed her the dead belt, part number clearly showing, and said “I need one of these”. After a quick parking lot install, in the rain, off I went again with 14V on the meter.

    So, I’m a fan of volt meters.
     
  25. cluxford
    Joined: Jun 5, 2012
    Posts: 53

    cluxford
    Member
    from Australia

    Slept on it...ordered a voltmeter this morning. Only $100 (Dakota Digital as I have their Odessy Series clock in it also, so it will match)
     
    firstinsteele and pprather like this.
  26. @cluxford , @Crazy Steve
    Request granted. You got schooled, well, we all did today. Great explanations.
     
  27. If you are looking for a good 2 wire locally available alternator, early Holden Commodore Bosch are easy to find at swap meets, and you can change the regulator while fitted in the car. One terminal to the battery, one to the idiot light.
     
  28. I wish you hadn't mentioned that.
    But then, you also mentioned 'front runner system.' :eek:
     
  29. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 1,425

    427 sleeper
    ALLIANCE MEMBER

    According to the diagram in post #17 above, couldn't you connect all 3 wires to the battery terminal on the back of the alternator and have everything work as designed, so to speak? If not, what am I missing?
     
  30. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 1,425

    427 sleeper
    ALLIANCE MEMBER

    What about the upper diagram for the 10SI? Would that work?
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.