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Discussion Starter · #1 ·
I store my 07 for 8 months a year and i dont like leaving it on a tender at the house for that long without anyone home. So i installed a simple battery disconnect on the negative terminal. After a cple hundred miles i got a transmission change error. I thought maybe the switch was defective so i tried a new one. Same error. Can anyone explain why?
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2003 mk3 4.4L
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did you ever turn it off with the ignition on? (major no-no)

also, what current rating does that switch have? doesn't look like one that supports 900+ CCA
 

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2006-2009 Range Rover MkIII / L322
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I’ve had mixed results with these cheap battery disconnects and try to avoid them now. They always have signs of electrical arcing damage whenever I replace them, regardless of how carefully is install and tighten them. I also suspect that some fault codes in the past were due to an unreliable connection to the battery. If you are storing the vehicle for a single time or only a few times a year, consider removing the negative terminal.

There are also much better quality battery disconnects out there. Have a look at Blue Sea Systems products in the marine world.

They have a nice, but expensive, 500 A (continuous) / 700 A (5 min) Remote Battery Switch (part # 7700). It’s basically a large bi-stable relay with a manual override knob on the unit plus provision for a remote wired switch. I use one of these to isolate the winch on my D2.

They also have manual only battery switches rated to 350A (continuous) / 600A (5 min) / 1200 A (cranking) (part # 9003e) and 600A (continuous) / 900A (5 min) / 1750A (cranking) (part # 3000).
 

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Discussion Starter · #7 ·
I’ve had mixed results with these cheap battery disconnects and try to avoid them now. They always have signs of electrical arcing damage whenever I replace them, regardless of how carefully is install and tighten them. I also suspect that some fault codes in the past were due to an unreliable connection to the battery. If you are storing the vehicle for a single time or only a few times a year, consider removing the negative terminal.

There are also much better quality battery disconnects out there. Have a look at Blue Sea Systems products in the marine world.

They have a nice, but expensive, 500 A (continuous) / 700 A (5 min) Remote Battery Switch (part # 7700). It’s basically a large bi-stable relay with a manual override knob on the unit plus provision for a remote wired switch. I use one of these to isolate the winch on my D2.

They also have manual only battery switches rated to 350A (continuous) / 600A (5 min) / 1200 A (cranking) (part # 9003e) and 600A (continuous) / 900A (5 min) / 1750A (cranking) (part # 3000).
Thanks for referral. Which blue sea shld i go with exactly? I dont care about price. I just want to be able to lift the hood and disconnect without having to pull the negative every time.
 

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Something doesn't add up. Can you measure to see if there is any resistance in the switch?
electrical meters won't show issues at high current levels. during cranking at hundreds of amps, the connection will heat up and the voltage may drop 2-5V or more. this sag can trip out all the various control modules. however, measuring voltage across the switch may show the problem. if there is any voltage from the battery terminal to the cable connection during start, that will prove the problem
 

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Takes 2 secs to put an ohm meter on it. And resistance is resistance, R, no matter what voltage or amps is on the circuit. The fact that it's taking a few hundred miles and only the transfer case motor or circuit throws a code is weird. That fault code should be stored, so LR is erasing it, or it clears itself.

what's this?
 

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electrical meters won't show issues at high current levels. during cranking at hundreds of amps, the connection will heat up and the voltage may drop 2-5V or more. this sag can trip out all the various control modules. however, measuring voltage across the switch may show the problem. if there is any voltage from the battery terminal to the cable connection during start, that will prove the problem
I totally agree with this statement. The arcing at high current level can lead to very non linear voltage drop vs current.

When these cheap switches are new and tight they work fine, and I have used them on many vehicles. Once they start to show signs of arcing, it’s better to replace them.
 

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Not worth the effort.
The switch (the one that was in the 07) works fine in my escalade and maserati. It’s something with the 07
I’ve had this exact symptom but in my case it was a loose battery terminal. I’m not suggesting that there may not be other issues, but the battery disconnect is a probable root cause.

A simple way to check is to remove the screw completely and check for signs of arcing.
 

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Thanks for referral. Which blue sea shld i go with exactly? I dont care about price. I just want to be able to lift the hood and disconnect without having to pull the negative every time.
After reviewing the specs again, I think the Blue Seas Systems 6006 (red) or 6006200 (black) would be suitable. This is a 300 A continuous On-Off switch which can handle a cranking current of 900 A for 30 seconds. It provides a bit more protection for the back of the switch and is not as overspec’d as the versions I listed previously.

If it were my vehicle, I would use the black switch on the negative circuit. Detach the earth cable from where it connects to the vehicle body and attach to one side of the switch. Add a short cable of the same wire gauge from the other side of the switch to the body.

When using, remember to let the vehicle sit for a minute or so after keying off before disconnecting the battery to allow for an orderly shut down of the computers.
 

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Discussion Starter · #15 ·
After reviewing the specs again, I think the Blue Seas Systems 6006 (red) or 6006200 (black) would be suitable. This is a 300 A continuous On-Off switch which can handle a cranking current of 900 A for 30 seconds. It provides a bit more protection for the back of the switch and is not as overspec’d as the versions I listed previously.

If it were my vehicle, I would use the black switch on the negative circuit. Detach the earth cable from where it connects to the vehicle body and attach to one side of the switch. Add a short cable of the same wire gauge from the other side of the switch to the body.

When using, remember to let the vehicle sit for a minute or so after keying off before disconnecting the battery to allow for an orderly shut down of the computers.
Thanks!


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How are you going to install that? Build up a console panel in the engine bay?

Wouldn't it be easier just to run a cord to a mini Noco smart charger and plug the car in?
I hook-up my NOCO every month or so, just to keep my battery at peak 100% performance.
 

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Discussion Starter · #19 ·

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Your alternator is rated to 150A. This switch is rated to 100A. If your battery is severely depleted, you could exceed the current rating of this switch as the alternator charges the battery.

There are plenty of options out there, but start with a unit that exceeds the capability of your system to charge or discharge the battery.
 
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