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Discussion Starter · #1 · (Edited)
I’m wrapping up a multiyear restoration of my 77 Shadow II. During this time, the battery ran down multiple times, and we’ve charged it and jumped the car and done all kinds of things we probably should not have done moving the car around my shop.

Now that the car is basically finished and roadworthy, I’ve noticed that the battery was running down over the course of a night.

Obviously, this is an issue I’ve been trying to resolve as quickly as possible. The first thing I did was pull all of the fuses which made no difference. I’m actually measuring 12 V on the frame of the car which is pretty scary.

We did install a new starter so that was my first thought but removing the starter and the alternator from the circuit still does not resolve the issue.

if I apply 12 V directly to the main feed going to the shunt with all fuses disconnected I get the draw. I’m wondering if my ammeter shunt has blown.

has anyone experienced anything like this?
 

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I find the culprit by clipping in a DC ampmeter between the positive batt terminal and the cable itself. You will probably see a reading, then start poking around by pulling fuses, toe board connectors (helpful to localize), and possibly defective diodes. What you know is something failed and it's within the confines of the car....you'll find it if you got this far. I know the journey well.
 

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I was guessing has this guy thinks a blown shunt could cause a draw!. I'm also guessing it's positve earth as he says" I’m actually measuring 12 V on the frame of the car which is pretty scary. ?
Thats why I think he's no electrician , I could be guessing wrong?
Mike
P.S. I agree a bad electrian is worse than an ametuer who asks for advice!
Mike
 

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Discussion Starter · #6 · (Edited by Moderator)
I actually don’t know what’s causing the draw. I have almost 7 years of experience working on these cars and this is an unusual situation. And yes, if I take a voltage reading on the negative side of my car, I’m getting 12 V, it’s like the chassis of the car has been electrified. I also have a Mercedes-Benz factor train tech that works for me in my shop with 30 years of experience and he has stumped on this as well. The whole point of these forms is to be helpful. I’m not some yahoo that’s never had a Rolls-Royce I own four of them.
 

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Michael - Please stay with the group and don't let one person's rude comments put you off. It's clear you know what you are doing.

Here's a thought - The steel frame that clamps the battery in place is perilously close to the positive battery terminal. If the clamp loosens and touches the terminal you have a direct short to the frame of the car. Of course, this would result in a fire, however I'm wondering if crud/oil/grease etc on the positive terminal could be causing the leak by offering a high resistance path to earth. Just a thought, but worth checking. I've wrapped the clamp with insulating tape on my car, where it gets close to the positive terminal.
 

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I’m wrapping up a multiyear restoration of my 77 Shadow II. During this time, the battery ran down multiple times, and we’ve charged it and jumped the car and done all kinds of things we probably should not have done moving the car around my shop.

Now that the car is basically finished and roadworthy, I’ve noticed that the battery was running down over the course of a night.

Obviously, this is an issue I’ve been trying to resolve as quickly as possible. The first thing I did was pull all of the fuses which made no difference. I’m actually measuring 12 V on the frame of the car which is pretty scary.

We did install a new starter so that was my first thought but removing the starter and the alternator from the circuit still does not resolve the issue.

if I apply 12 V directly to the main feed going to the shunt with all fuses disconnected I get the draw. I’m wondering if my ammeter shunt has blown.

has anyone experienced anything like this?
Hey Michael. One responder is very correct in saying you should disconnect the plus side of the battery and put a meter between the terminal end and the positive terminal. Then pull the fuses one at a time watching for a change in the meter values. This can help isolate the circuit thats shorting. Assuming you have already tried this I'll share two shorts I found in my Silver Shadow. One was in the dome lights caused by wires shorting in the headliner. I finally ran new wires between the lights so as not to damage the roof liner. The second was a dead short between wires hidden in the D pillar. These ran to the trunk light switch and the vanity lights in mirror on the drivers side. In both cases the wires were melted and touching body parts. They had to be cut out and spliced. Good luck. One further note I sold my Shadow and regretted it ever since. Rollsroycerescue.

Moderator note: There is no need to quote a previous post when you are replying if you are following the train of thought in the thread, it just clutters up the thread unnecessarily. Do not click on "reply", as this automatically adds the previous post to your reply. Just start typing your reply in the dialogue box at the bottom of the thread where it says "write your reply".
 
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