1975 Dart Sport - Alternator Issue?

Electrical and Ignition

  1. Logan Haun

    Logan Haun Well-Known Member

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    Hey all,

    I got my first running a-body a few weeks ago. The car has a 225 slant six with factory ac. The previous owner installed an electric fuel pump, new starter, gps, and backup camera(I have since disconnected the gps). The car starts easy when it is cold.

    The car was missing the dome light bulb. About two weeks ago I installed the dome light bulb. The bulb comes on when the doors open. However, after installing the bulb the car would hardly start and once it started it ran really rough. I removed the bulb and the car was able to start and after a minute or so it ran fine. My initial thought was that the bulb had a short or something and was pulling alot of current(not an electrician).

    I tested the battery with my multimeter and it checked out(12.5 volts or so). I ended up starting the car and running it without the bulb. I hooked up my multimeter and the battery was around 14 volts. With the car running I put in the bulb and turned all the accessories on(ac, lights, left doors open so bulb is on) and I hooked up my multimeter. The battery voltage slowly dropped until it got to around 12.3 volts and the car started to run rough. I took the bulb back out and again the car ran fine. Today I ran the car with bulb out and turned all the accessories on. The battery voltage was initially around 14 volts but as I let it run it got down to under 13 volts.

    One site I read told me to test for ac voltage across the terminals to determine if there is a bad diode. I set my multimeter to 200 ac volts and I got around 30 volts ac across the battery terminals.

    I pulled the alternator and took it to my local auto parts store to have it tested. They tested it three times and said it was good.

    The alternator that is on the car is a single pulley alternator(I think).

    I'm not quite sure what to do at this point? I don't know if I should purchase a new alternator? If so should I get another 60 amp alternator or 100 amp alternator?

    I appreciate any help.

    Here is a picture of the alternator.

    alternator.jpg
     
  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    I doubt "that particular bulb" is causing the issue. Try the same tests with the parking lamps and or headlights.

    Very FIRST thing to check is the belt tension and check the belt and pulleys for slippage and glazing

    With everything in the car you can think of, the heater, lights, etc, the alternator should be able to maintain a minumum of 13V at least after it has recovered from the starter

    So start and warm it and monitor battery voltage. Run it at a good fast idle to simulate a cruise of at least 35mph. Then turn on various accessories and see if it keeps up

    There are further tests don't go replacing parts just yet
     
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    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      Looks like the original alternator. Way cool! cool-gif.gif
      There might be assembly date and part number stamped in the rear casting, and the tag on the front half is the factory identification info. Its color coded according to amp 'rating'.
      upload_2020-5-29_15-57-36.png

      This is almost certainly the cause of all the problems. (a) The electrical system was not really designed for extra electrical loads at idle. (b) the alternator was not designed to produce the additional power needed for these accessories. (c) The method and location of tapping into the existing system to add these things may be be contributing to issues.

      A bulb can have an 'open'. It is possible to have a short in the dome light wiring. It would have to be at or before the dome light on the feed side. If so, the fuse should blow.

      A little low. Not terrible. 12.8 V would be better.
      You've just proven that the alternator is not producing enough power to run all of the accessories at the same time. Or possibley, a poor connection in the output wiring is getting hot, and the hotter it gets, the more resistance it has to flow.
      In either case, the problem is not the dome light per se.
      The one electrical load we don't know in either of your tests was the battery.
      That can be a big variable. If its really low on charge, it could be sucking 20 or 30 amps at 14 Volts. On the other hand, if it was fully recharged, it would draw nothing measurable at 14.0 Volts.
      The ammeter will indicate whether the battery is charging or discharging assuming the electric pump and camara was wired into the fusebox.
      If that stuff was wired to the battery positive or the junction at the starter relay, then that's not true any longer.

      Well that can't be. So maybe just a bad test.

      My suggestion is:
      Figure out where the electric pump and back up camara are wired in.
      Make sure the dome light is still properly fused.
      If it was me, I'd put a mechanical pump on it and also remove the back up camara. These cares have pertty good viewing all around. But the backup camara is really not a problem itself. It should be wired into the accessory side of the fuse box.

      As best I can tell, '75 wiring is still somewhat like this. (76 is very different).
      upload_2020-5-29_16-28-43.png
      Important things to notice are:
      The ammeter is located to show current flowing in or out of the battery.
      The fuse box has some circuits directly wired to the battery and alternator. One of these is the dome light.
      The box also has circuits that are only turned on when the key is in Run or Accessory.
       
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      • cudamark

        cudamark FABO Gold Member FABO Gold Member

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        The way to test your charging system is to have everything installed on the car and run a load test. Most good shops should have a carbon pile load tester. It may be that the alternator is working just fine and the regulator isn't. Simple fix if that's it, but, you won't know for sure without a full system test. Your year has notorious wiring problems, mostly at the bulkhead connector. Any corrosion in that connector can cause all sorts of electrical issues. Depending on where some of your add-on accessories were tapped in, you may be overloading one or more of those connections. Only install an alternator with the proper rating for your wiring harness. All the ratings up to 60 amp use the standard harness. Higher output ones such as the 100 amp you mentioned need a heavier duty harness, different ammeter, and a different voltage regulator.
         
      • Logan Haun

        Logan Haun Well-Known Member

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        I know this is an old thread - but I just had a chance to work on the Dart. Here's where I am at:
        • I had the battery tested. It failed. I purchased a new battery and put it in the car. I ensured all battery connections are tight. I drove the car - the car died 3 times - all 3 times while slowing down at a stoplight.
        • I was removing some extra's from the car(backup camera, gps, etc...), and I took a look in the engine bay. I noticed that there is quite a bit of stuff that looks jerry rigged. I noticed that what appears to be the ported vacuum hose is just hanging out in the engine bay - not connected to anything(see picture). There is no evap canister in the engine. Could this be affecting the engine performance?

        EvapCanister.jpg
         
      • cudamark

        cudamark FABO Gold Member FABO Gold Member

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        If it only dies while slowing down, that sounds like a carburetor problem. Does it idle properly otherwise?
         
      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        An alternator should not cause the car to die unless for some reason the battery was already low. Here' an example. In my early days (early 70's) I had a 440-6 70 Roadrunner. I did not realize the battery was sulfated, and caused overcharge. I had moved the battery to the trunk. A friend of mine and I made a mad dash on a weekend from San Diego to Vegas. Damn battery about stunk us out through the trunk/ back seat. Next day we drove back WITH THE REGULATOR UNPLUGGED. Drove the care most of the way from Vegas back to San Diego WITH NO WORKING ALTERNATOR. I plugged it back in at some point thinking the battery was getting low. This was only running the ignition, no lights, no pumps, no stereo

        You can not do that nowadays, with EFI
         
      • MOPAROFFICIAL

        MOPAROFFICIAL FABO Gold Member FABO Gold Member

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        I should have read it all..
        Check that wire for a short.
        Then...
        Jump the + field to the bat terminal on the alternator and see if it full charges, if not... change the alternator.
         
      • Logan Haun

        Logan Haun Well-Known Member

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        It does seem to idle fine otherwise. There are times however that I have hooked up a multimeter and ran the car with the accessories on and the battery starts to drain - to the point where it starts to rough run and then dies.

        I have a feeling that I've got multiple issues going on here.
         
      • Logan Haun

        Logan Haun Well-Known Member

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        I'm sorry - I don't quite understand. When you say jump the + field to the bat terminal on the alter are you saying to run a wire between the positive terminal on the battery and the positive terminal on the alternator?
         
      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        No run a jumper from the battery + terminal to the field terminal of the alternator after you have disconnected the green wire. It should put out "full." If it does not the alternator is weak or non functional. Watch the battery with a voltmeter and slowly bring up RPM. Don't allow it above 16V or so. Turn on all loads, lights, heater, all you have, bring up RPM and see if it will come up above at least 13 or better
         
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