Electrical Mystery

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  • ckiczenski
    230 Tornado
    • Apr 21, 2014
    • 10

    Electrical Mystery

    I have a very weird electrical problem on a 78 J10 258.
    Let me rule out what it isn't by listing what I've done:
    Voltmeter swap / alternator charging circuit rewire, HEI distributor, Good battery, good starter, new starter solenoid, GROUNDS ARE ALL GOOD REDONE OR ADDED, New + battery cable (with soldered eyelets), New ignition switch
    Now let me explain whats going on.
    Was driving the truck daily with no issues. Parked it during December & January then it wouldn't start. Key wouldn't do anything. Started tinkering with it and noticed there was no headlights, no horn, no wipers, no power to anything. I know grounds are a huge deal so even after redoing all my ground connections i took a jumper cable from the - post and clamped it to various spots on the body & frame. Still no change. I have 12 volts from battery to firewall plug at the red and yellow main feeds. Inside the cab I initially have 12v to the ammeter terminals. With a voltmeter hooked up to these wires and i try to crank the engine as soon as i crank the key volts drop to 3v and then slowly climb back up to 12 volts. I can visually watch the headlights slowly come on and get brighter if i leave them on after trying to start. Volt meter hooked up to the battery with same procedure it reads a constant 12.2V no change when cycling the key. I've also tried unplugging nearly every accessory to try to isolate the issue but still no change.

    I am able to turn the key into run position then jump the solenoid with cables and engine fires up. Once it fires up I have 100% power to everything (headlights, horn, wipers, etc). I shut it off then its back to no power again.
    It cant be the fusible link because 1) I've tested good continuity and 2) it is in the yellow main feed which doesn't go to anything with key off. the red main wire goes to the wire junction and powers everything when off.

    I've exhausted nearly possibility and am very grateful for any advice!
  • 78 WIDETRAC
    350 Buick
    • Aug 19, 2003
    • 844

    #2
    This was what I did yesterday.


    I know that you said all of your grounds are good. Just hear me out.





    So basically something similar happened to me. I bought a running 79 Cherokee. I needed to fuel tank replaced. So I got it up to my place, Started and drove it off of the trailer using a gas can. Park it in the driveway a couple of months go by, I finally get the fuel tank back in and go to fire it up and I get nothing.


    I have a fresh battery & Power to the solenoid and to the starter, but nothing in the cab or fuse box.



    I removed the starter cable from the solenoid and touched it to the battery connected post on the solenoid, and it cranks. hook it back up and still get nothing from the ignition key.



    Then I remember having problems not having a ground from the neg cable to the fender in the past. So I figured it was worth a try. after I added that cable the damn thing fires with the key, and the headlights are back on etc...



    So after all of that It was a missing ground from the neg battery cable to the fender. I used a 4 gauge battery cable. The one to the block was not enough apparently.

    Comment

    • babywag
      out of order
      • Jun 08, 2005
      • 10284

      #3
      Just because the parts are "new" doesn't mean they cannot be bad.
      Electrical aftermarket parts are a roll of the dice.
      Double check the solenoid and the ignition switch.

      A 40yr old Jeep can also have hidden electrical/wiring issues anywhere in the harness.
      A common issue on these is the main large gauge feed wires @fuseblock can be damaged.
      I have seen the insulation rubbed down to copper from decades of service and also with melted insulation from ammeter issues.

      May take a while but you'll need to check end-end of suspect circuits to find/repair the issue.
      Tony
      88 GW, 67 J3000, 07 Magnum SRT8

      Comment

      • ckiczenski
        230 Tornado
        • Apr 21, 2014
        • 10

        #4
        Hey guys thanks for the replies and insight.

        Had some time this afternoon to continue messing with the truck and I found the problem.

        I first tried unplugging the main junction at the firewall and jumping the solenoid wire pins with a 12v lead and still saw the volts drop way down like before. I did this to factor out the interior harness from the problem. I was certain my engine bay harness is good, so i played around with the main battery cables thinking maybe a cable has a bad / high resistance spot internally. I tried starting the truck and the solenoid clicked this time which is progress.
        I felt like it had to be the battery. I took the battery out and gave it a good shake, threw it back in and it fired right up, no issues!!! My battery does not have the fill ports but it likely is low on water.
        So, I was totally overthinking this issue. If someone reads this thread in the future with a similar problem, I HIGHLY recommend double and triple checking the basics first. Start simple and go from there.

        Comment

        • DarkMonohue
          Shakes hands with danger
          • Jul 01, 2012
          • 1145

          #5
          Originally posted by ckiczenski
          So, I was totally overthinking this issue. If someone reads this thread in the future with a similar problem, I HIGHLY recommend double and triple checking the basics first. Start simple and go from there.
          Truer words were never spoken. This should be required reading for anyone attempting any repair on any vehicle, but especially on dilapidated American iron that was indifferently assembled a minimum of thirty years ago, and since then, has probably been creatively re-engineered by no less than five previous owners with an average education level somewhere between the federal prison system and "ain't never saw no need for book learnin' anyhow".
          '85 J20 Old Man Truck, bought @ 65K miles - not great, but better than walking.
          Member, FSJ Prissy Restoration Association
          High quality junk here: intro thread and slow build thread

          Did you know? Willys is just Willis spelled differently, but pronounced the same. Neither Willy nor his apostrophe are involved.

          Comment

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