Chasing short thru fuse block - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

 
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post #1 of 6 (permalink) Old May 1st, 14, 6:23 PM Thread Starter
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Chasing short thru fuse block

I'm having some sort of parasitic draw from somewhere but can't pin point and need some input.

When testing the amp draw from battery I noticed something was way wrong; it showed a draw at 20 amps.
I disconnected battery and started looking for shorted + - circuits.
Fused link at starter (brown) that starts as red (battery 12V) from fuse block was reading as a short to negative battery. Chased it to the fuse block and started to pull fuses.
Half of fuse block (left) was reading as a short before I pulled fuses.
Now I get "dash lights", "clock", "park lights" and "courtesy" as possible shorts. Pulled the headlight switch and I have a connection between Dimmer switch (yellow) and chassi ground. Cannot see any naked wiring or loose connections under dash or at headlights.
Right now I'm a bit at a loss of ideas of where to troubleshoot.

Also, I get connection between green horn wire and chassi ground at the horn relay, not sure if that is right?

I installed this wiring about a year ago and it has worked without problem until now, it's a kit from American Autowire.
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post #2 of 6 (permalink) Old May 1st, 14, 7:26 PM
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Re: Chasing short thru fuse block

Quote:
Originally Posted by Hank327 View Post
I'm having some sort of parasitic draw from somewhere but can't pin point and need some input.

When testing the amp draw from battery I noticed something was way wrong; it showed a draw at 20 amps.
I disconnected battery and started looking for shorted + - circuits.
Fused link at starter (brown) that starts as red (battery 12V) from fuse block was reading as a short to negative battery. Chased it to the fuse block and started to pull fuses.
Half of fuse block (left) was reading as a short before I pulled fuses.
Now I get "dash lights", "clock", "park lights" and "courtesy" as possible shorts. Pulled the headlight switch and I have a connection between Dimmer switch (yellow) and chassi ground. Cannot see any naked wiring or loose connections under dash or at headlights.
Right now I'm a bit at a loss of ideas of where to troubleshoot.

Also, I get connection between green horn wire and chassi ground at the horn relay, not sure if that is right?

I installed this wiring about a year ago and it has worked without problem until now, it's a kit from American Autowire.

Are you sure you are reading your current right? 20 amp draw???? All 4 headlamps on a 4 lamp vehicle when activated, don't even draw 20 amps...

I'm questioning your methodology on "seeing a short". Are you taking resistance readings?

A simple resistance test is not the way to go. With the battery disconnected, you'll see a "short" to ground on the any main positive lead if the door is open or the clock is in "rewind" mode.

What year of car? '72 ?? What kit from American Autowire??? Is this a stock replacement harness or Update harness?

The simple way to determine a short/current draw is install a test lamp in series with the negative battery cable. The light continues to light until all power drawing circuits are removed. It's a matter of divide and conquer. Start with underhood connections (alternator lug, junction block connections, 1 at a time).

If your car has a factory clock, just pull the courtesy fuse right away. This will get rid of nuisance items to begin with, courtesy lamps and clock.

-If you don't stand for something, you'll fall for anything.
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post #3 of 6 (permalink) Old May 2nd, 14, 5:11 AM Thread Starter
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Re: Chasing short thru fuse block

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Originally Posted by Coppertop View Post
Are you sure you are reading your current right? 20 amp draw???? All 4 headlamps on a 4 lamp vehicle when activated, don't even draw 20 amps...
Thanks Coppertop for taking the time to help out.

Yup, I'm sure it was 20 amps I saw, all pointing to the starter. What I know so far is that the semi big wire coming from the fuse block (labeled 12v battery) is not shorted when headlight switch is pushed all the way in, but if I put the lights ON the red wire gets a connection between negative battery cable and itself. That one is usually hooked to the + on the starter, with the big battery + and the alternator fused cable. Did I hook the mini starter up wrong?

Quote:
Originally Posted by Coppertop View Post
I'm questioning your methodology on "seeing a short". Are you taking resistance readings?
Yes, I'm taking resistance readings, mostly because of the major draw if I hook up the battery right now.

Quote:
Originally Posted by Coppertop View Post
A simple resistance test is not the way to go. With the battery disconnected, you'll see a "short" to ground on the any main positive lead if the door is open or the clock is in "rewind" mode.
Ok, but with all fuses pulled except dash lights and doors closed, should I still get a "short" to ground at the starter?

Quote:
Originally Posted by Coppertop View Post
What year of car? '72 ?? What kit from American Autowire??? Is this a stock replacement harness or Update harness?
The car is a 65 El Camino, with AAW kit no. 500981 (classic update series).

Quote:
Originally Posted by Coppertop View Post
The simple way to determine a short/current draw is install a test lamp in series with the negative battery cable. The light continues to light until all power drawing circuits are removed. It's a matter of divide and conquer. Start with underhood connections (alternator lug, junction block connections, 1 at a time).
I think that is kind of what I started with, using the amp meter to check for parasitic draw from battery negative, but I might be wrong. It just felt a bit unsafe to hook the battery up and risking welding something.

Quote:
Originally Posted by Coppertop View Post
If your car has a factory clock, just pull the courtesy fuse right away. This will get rid of nuisance items to begin with, courtesy lamps and clock.
The courtesy fuse is out as well as park lights fuse and clock.
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post #4 of 6 (permalink) Old May 2nd, 14, 8:10 PM
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Joe
 
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Re: Chasing short thru fuse block

Ok Hank

First off, if you use the "test" light method, you won't "weld" anything as the light in series with the negative cable will act as a current limiter. A dead short will cause the light to glow bright, where as a small drain will cause a dim light.

As far as your resistance readings go, you must take a look at the "big picture". If I take a normally operating vehicle and disconnect the battery, then take an ohm meter and measure from the positive cable to chassis ground, there are many instances you will see what appears to be a "dead short" to ground. Turning on the headlights for example will cause this. The minute you pull the switch, you link the positive feed thru many filaments in the bulbs to ground, this looks like a short to your meter. Same thing if you measure the "S" terminal on the starter solenoid to ground, your meter would read "through the windings" and see a short to ground.

At this point, if you have a 20 amp draw, that is a serious draw. I would focus on the the old divide-and-conquer method to split up your electrical system. The 2 big suspects right away would be bad alternator and bad starter.

I'm not sure how the update series works underhood, (I belive they mimic the 1972 and later chevelles where all the power for the car is "tapped" off of the battery (+) lug on the starter solenoid), if that's the case, then what you need to do is:

Leave only the big battery (+) cable connected to the starter solenoid's battery stud, remove the feed(s) that supply power to the rest of the car. Check for a current draw. If there is a current draw, the starter is bad.

If there is no current draw, you add one connection at a time. If there is only one other connection to the battery (+) stud, add it, and check your current draw. The next step would be disconnect the main (+) lug on the back of the alternator to see if the draw goes away.

remember to completely disconnect the battery before each installation and removal of wiring components, then reconnect when your test equipment is set-up properly

A 20 amp draw should be quick to find, that amount of current and you, by right, should be smelling/feeling something "hot"!

-If you don't stand for something, you'll fall for anything.
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post #5 of 6 (permalink) Old May 6th, 14, 4:35 PM Thread Starter
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Re: Chasing short thru fuse block

Quote:
Originally Posted by Coppertop View Post
Ok Hank

First off, if you use the "test" light method, you won't "weld" anything as the light in series with the negative cable will act as a current limiter. A dead short will cause the light to glow bright, where as a small drain will cause a dim light.

As far as your resistance readings go, you must take a look at the "big picture". If I take a normally operating vehicle and disconnect the battery, then take an ohm meter and measure from the positive cable to chassis ground, there are many instances you will see what appears to be a "dead short" to ground. Turning on the headlights for example will cause this. The minute you pull the switch, you link the positive feed thru many filaments in the bulbs to ground, this looks like a short to your meter. Same thing if you measure the "S" terminal on the starter solenoid to ground, your meter would read "through the windings" and see a short to ground.

At this point, if you have a 20 amp draw, that is a serious draw. I would focus on the the old divide-and-conquer method to split up your electrical system. The 2 big suspects right away would be bad alternator and bad starter.

I'm not sure how the update series works underhood, (I belive they mimic the 1972 and later chevelles where all the power for the car is "tapped" off of the battery (+) lug on the starter solenoid), if that's the case, then what you need to do is:

Leave only the big battery (+) cable connected to the starter solenoid's battery stud, remove the feed(s) that supply power to the rest of the car. Check for a current draw. If there is a current draw, the starter is bad.

If there is no current draw, you add one connection at a time. If there is only one other connection to the battery (+) stud, add it, and check your current draw. The next step would be disconnect the main (+) lug on the back of the alternator to see if the draw goes away.

remember to completely disconnect the battery before each installation and removal of wiring components, then reconnect when your test equipment is set-up properly

A 20 amp draw should be quick to find, that amount of current and you, by right, should be smelling/feeling something "hot"!

Hi Coppertop,

Many thanks for explaining how to read and not to read resistance and how to chase the amp draw, it makes a lot more sense now.

I have to admit that it was a pretty easy to find problem, but of course I had half the dash out before I saw it... I had been doing some R&R at the transmission lines, and therefor taken the starter off and on again what I didn't see was that the big + coming from the battery to the starter had a pretty big L-shaped shoe which was tilted and made contact with the negative post on the starter. I guess I got way too caught up in thinking about the resistance and a short to ground under the dash...

Anyhow, thanks again for helping out!
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post #6 of 6 (permalink) Old May 6th, 14, 7:24 PM
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Joe
 
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Re: Chasing short thru fuse block

Glad you got it. I had to be something like that with such a large current draw. I'm glad no damage occurred to your vehicle, main B+ shorts to ground can be quite dangerous.

-If you don't stand for something, you'll fall for anything.
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