No start; no juice with the key in on or start positions but accessory works fine

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Joined
Jun 14, 2019
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Location
Coachella Valley (Palm Springs)
My Car
1973 Convertible, 351 4v CJ, C6, Mach 1 Decor options, power: steering, brakes and windows, a/c, Rally Pac gauges, Deluxe interior.
[url=https://ibb.co/ZVjjKXW][img]https://i.ibb.co/zrMMbxG/s-l1600-2.jpg[/img][/url]
After two weeks of just sitting, went for a drive. Was merrily tooling around the 'hood this weekend and gave it a little goose on the last block before home. Instantly from under the hood a pop (like a backfire into the carb) and the car quit. Coasted to a stop and when trying to start, 100% dead as if there were no battery at all. Connected my portable battery and started right up so drove home. Put a low rate charger on the battery overnight.

Next day when trying to start: na-da. nothing. zilch. But I noticed that since I had the car door open and the courtesy lights were on, when I turned the key to on or run, the courtesy lights all dim down to barely noticeable then when the key is turned to off or lock, they do a slow brighten back to normal.

Today, before attempting to start, I checked the battery and it's showing 12.76v. Same business as before: courtesy lights and radio run fine until I turn the key, then everything goes dead and slowly climbs back to normal. No starter engagement at all. Also, using the convertible top switch causes the same "lights off, slow return to normal" behavior whether the key is on or off, as does turning on the headlights.

So then I connect my portable battery pack (it worked once before, right?) and within 2-3 seconds of turning it on, it's internal circuit breaker starts recycling continuously. Now when I turn the key to any powered position (on, run, accessory) the lights & radio turn off like before, but return to normal quite quickly -- no slow ramp up. Still, no starter engagement and any other high-draw electric (headlights, convertible top motor) triggers the on/off cycle. Car battery still reports 12.7v. The only difference I can tell between with and without the battery pack is that "recovery" is much, much quicker when the battery pack is attached.

All obvious connections (battery posts to cables, positive battery positive to solenoid, battery ground to sidewall, etc) are sound.

Clues?
 
Joined
Jun 14, 2019
Messages
453
Reaction score
79
Location
Coachella Valley (Palm Springs)
My Car
1973 Convertible, 351 4v CJ, C6, Mach 1 Decor options, power: steering, brakes and windows, a/c, Rally Pac gauges, Deluxe interior.
[url=https://ibb.co/ZVjjKXW][img]https://i.ibb.co/zrMMbxG/s-l1600-2.jpg[/img][/url]
I had a similar situation a few years ago. Turned out the battery was bad, went from starting the engine one time fine, next time nothing.
You can likely have the battery load tested at a car parts store.
Thanks, Doug. You nailed it -- and fortunately, that's an easy fix. Swapped batteries, started right up. Headlights are bright(ish) and top works.

I guess I've been down in the weeds looking for complicated solutions to obscure electrical issues for so long, I forgot to start with the simplest possibilities first. Then again, with the crazy-a** situation the last two+ years I had not realized I'd had the car for three years already! Battery was the culprit.
 
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