 Battery Isolator: Any benefit?, What's the nominal "off" current? |
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| LikesSummer |
 Aug 20 2026, 01:23 PM
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#1
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Newbie  Group: Members Posts: 6 Joined: 27-March 26 From: Ontario, Canada Member No.: 29,327 Region Association: Canada  |
So assuming one has an unmodified car, what's the key-out, "off" current on these? I've got a 72 4 which doesn't even have a radio. I could certainly go through the wiring diagrams and determine this for myself if this is potentially anything other than zero, but there's a good chance I'll miss something quirky, so I'm asking the experts.
If turning the car off brings the background current to zero, then there's no need for an isolator obviously. |
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| flipb |
Aug 20 2026, 02:28 PM
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#2
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Senior Member Group: Members Posts: 1,896 Joined: 2-September 09 From: Fairfax, VA Member No.: 10,752 Region Association: MidAtlantic Region 
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Cars with appearance group have a clock. Most of them quit working decades ago but the ones that work would have some draw. I also noticed that my (presumably dealer-installed) radio isn't switched by the car's ignition so I have to make sure it's turned off.
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| Ninja |
Aug 20 2026, 02:46 PM
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#3
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Member Group: Members Posts: 280 Joined: 25-September 25 From: Granbury Texas Member No.: 29,004 Region Association: Southwest Region |
Without a radio (with a memory circuit-modern) or a clock it should be zero.
Easy way to determine. Pull negative cable off of battery, attach a test light or DVOM (amps) between the cable and terminal and you'll have your answer. |
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| 930cabman |
Aug 20 2026, 03:17 PM
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#4
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Advanced Member Group: Members Posts: 4,794 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States
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my 1975 example with the appearance group always has a small spark when I connect/disconnect the battery. I have never measured, but also never had an issue with a dead battery.
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