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Old 07-16-2007, 01:36 PM
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Finding a short

IS there an easy way to find a short. The battery in my Vette dies on me every couple of days. Ive started with the things that don't work in the car IE: Battery Gage, (Was shorted to ground) Clock, assorted warning lights everything I checked other that the amp meter checked good. Then I found the windshield wiper motor, Or should I say the first 4 layers of skin on my forearm found it!! Oh it was hot! I figured I had my electrical problem licked I pulled the plug got a big spark and ohmed through the wiper switch which was bad. That was Saturday I went to drive her today and it was dead again. This time the battery was toast from being jumped so many times
Is there an easy way to find a short? The battery does spark pretty good when connected Thats why I think I still have a problem. Does anyone know any common problems with the 76 Vette?
Thanks!!

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Old 07-16-2007, 04:02 PM
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Doc here,

First of all..

Because you pulled the plug off the wiper switch, does NOT Isolate the wiper off power..PULL THE FUSE!

The wiper switch selects GROUND to the motor, (NOT POWER) and the motor is wired Direct to the fuse for power..The motor could STILL be internally shorted and drawing power..HOWEVER if it is wired correctly, would only do so in the RUN position..not just sitting.

NEXT, The complaint you have is Common to ALL GM Vehicles..

The most likely suspect is the (if you have an internally regulated alternator)Diodes are Reverse biasing (leaking backward) just sitting..ERGO: the worse off the diodes get the faster the drain..

To test, Get your DVOM out, CONFIGURE it for AMPS, and the highest scale, (usually 10 amps)Pull the battery cable, and place the meter in series with the battery and cable. BE SURE all loads are off ...(Dome, hood, Ctsy, Radio, undercarriage lamp..etc) Back scale the meter until it almost pegs the readout or just above "OL"..this will be your true reading.

The reading here will be between 0.3 and 0.8 of an amp (less than an amp) To be good.

IF it is higher, First , Disconnect all the wires off the alternator, then recheck your meter, IF it is within spec, or "000" , an Alternator rebuild or replacement is in order.

IF it does not fall within spec, remove ALL the fuses and relays, and while monitoring the meter , re~insert them. IF/WHEN the meter shoots up, that is an offending circuit, troubleshoot, repair or disable as required..then continue on (you may have more than one drain) until all are back in place and the reading is within spec.

Things that get "Stuck" and forgotten are : Power Antennas, high power audio amps, Defective alarms , Shorted horns that someone "just yanked the wire" from (the relay runs 24/7), Glove box lamps, Hood lamps (when closed) , under carriage lamps (yes , you have one, by the rear spare mount..) , Vanity mirror lamps, Electric Chokes connected improperly (12 volt source all the time), Stuck time delay timers.

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Old 07-16-2007, 06:32 PM
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Speaking of measuring amps, what's the best way to measure amps over 10 amps?
The meter can handle just 10 amps, which isn't very much.
Thanks.
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Old 07-16-2007, 07:16 PM
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Thanks Doc
I had a feeling you would be one of the posters on this one Thats some great Info THANKS!! I will get busy in the morning
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Old 07-16-2007, 09:05 PM
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Quote:
Originally Posted by scrot
Speaking of measuring amps, what's the best way to measure amps over 10 amps?
The meter can handle just 10 amps, which isn't very much.
Thanks.

Doc here,

Best and Cheapest is Rent an AMPROBE (inductive clamp on probe usually good up to 100's of amps..) and just clamp it around the battery cable.

Auto Zombie has These (usually) that all you need do is write a check for the purchase price, they hold the check, then when your done, return the tool , unbroken or molested, and you get your check back..

Now~A~Days I think AMPROBES have come down in price ..from like $300 last one I bought 20 years ago..(comml, 600 amp probe), to like $50 to $100 bucks..Also works on your home electrical..so If you have the need , they are a good addition to the 'Ol toolbox..good for balancing line loads , looking for spikes on the line and the like..

IF you just want a Cheapie, "test once in awhile" Meter that does not need to be too accurate, say, +/- 5 amps..

PARTS LIST:
  • Get a Plastic project box, rat shak, or ACE,
  • 30 Feet of #10 Gauge RED wire,
  • a Battery terminal clamp,
  • and a Battery Charger or jumper cable type Clamp,
  • and a Fairly decent -60 ~ 0 ~ +60 , automotive amp gauge,

ASSEMBLY:
  • mount the gauge in your project box, nice and neat,
  • Drill, and Strain relief the # 10 wires to your box, so they can't be ripped out..Cut the Wire in half, 2 ~ 15 foot lengths..
  • Connect the #10 RED wire with the cable terminal end to the + side of the gauge.
  • Connect the #10 RED wire with the Charger or Jumper cable type clamp To the - side of the gauge..
  • Close and seal the project box.
  • Test / Check calibration against a known accurate Current source, Write down any errors on the back of the box...(I.E. -2 Amp error At +50 amps)

You have a 60 simi~Accurate amp gauge for testing, for probably less than $20 Fazools..PLUS, with 15 feet of cable, you should be able to monitor the meter from the fuse box area, while connected to the system, without probe extensions or running back and forth front to mid car..

Doc
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Old 08-22-2007, 06:07 PM
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Doc, a belated thanks.
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