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Tech Question

Ken Schmidt, Huntington, NY, 1971 Dodge Dart GT ‘vert 340

While driving my electrical system shorted out and fried the fusible link and only the large wires to and from the ammeter. I suspected the main harness coming in through the bulkhead connector had worn through on the rear steering column support stud which points up into the harness.(later cars had a plastic sleeve around the harness that I have since installed)

Unfortunately, after removing the entire harnesss inside and out in the engine bay, and repairing all signs of damage, I still have an intermittent short. Being an electrician for 21 years and reading and rereading the service manual electrical diagrams, I am lost as to what to try. The car does not kill the battery while sitting. I checked/changed the headlight switch, wiper switch, and pulled all the fuses.

I had the entire rallye cluster out and ran the car with a differentammeter between the black and red leads. Every time I think I’ve isolated the culprit (ignition column wiring, factory tach, turn signal column harness…etc) the next time I start the car, the ammeter is pegged. While the cluster was hanging I kept trying to move wires to locate the short, and sometimes the short would stop, coincedence? I am about ready to quit, but you guys are usually find a wayto solve problems.

BTW, as long as I had the cluster out, I did the 5v I.C. regulator swap from a few years back that cured my dancing gauges, And, I swapped the leads to the electronic distributor from a more recent issue that fixed my tach’s high readings at low RPMs, just like you said it would. So could you please help me figure out what’s frying my electrics?

Oh, when I took the alternator and regulator to a rebuilder, the Alt was dead, but not shorted, and the regulator checked out fine. I also swapped out the starter relay and ECU with no curing of the problem. Sorry this is so long, almost as long as I’ve been trying to fix the problem, LOL. Thanks, Ken

Ken-

Whew! Okay, there are actually lots of clues here. The first is that thisonly happens with the engine running! The ammeter circuit is live at alltimes, key on, key off, engine running, engine stalled — so I’m leery of it(your current problem) being an actual charging system short at all. Plus,this usually, as you learned, cooks the fusible link, and more. Next, if theshort was on the battery side of the ammeter, the ammeter would not move atall (or, at least no more than the alternator’s maximum output rating), andif it was on the other side, it would be pegged to the left (I assume that,from your description, it’s pegged full-scale right). Think about it – thismeans that too much current is flowing INTO the battery!

Here’s my guess — a pretty educated one: The alternator has an intermittentshort in the rotating field. This causes it to go full-field (max charge)intermittently. This is one defect that’s almost impossible for therebuilders to catch. The fix: Get a BRAND NEW alternator.

If you’re a doubter, you can prove this by simply monitoring the batteryvoltage. If it shoots UP instead of down when the symptom occurs, you owe mea case of Pilsner Urquell!

I’ll be watching for the UPS man….

Rick

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