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Discussion Starter · #1 ·
After a dead battery the other day I have just spent the best part of an hour looking for the source of the current drain - DOH;oops: - I had left the interior light on. Now with everything turned off (inc the clock) I'm still getting a 0.35A current usage between the battery negative terminal and the earth. Is this significant or normal?- should there be 0A. I'm thinking the Lucas fuel ECU and radio will use a tiny amount to store their memory settings but even 0.35A sounds quite a lot for this?
 

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It does sound high to me, too, but see this thread. There are many suggestions there, but no final resolution published.

In my opinion, checking the grounds, as suggested in that thread, is not necessary for this particular issue; bad grounds cause problems, but not this one - a bad ground would cause less current to flow, not too much. To see which circuits are drawing current, with the ammeter in line, pull the fuses one at a time and note which ones have a noticable effect.
 

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Discussion Starter · #3 ·
Thanks Skip - I pulled all the fuses and relays and the drain is still there -no key in ignition either. By my calculations (watts=Volts x amps) I'm using 4.2w:eek:
 

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trackside said:
<snip> Now with everything turned off (inc the clock) I'm still getting a 0.35A current usage between the battery negative terminal and the earth.
Maybe I get this wrong, but between the negative bourne of the battery and ground they should be zero volts, zero amps, since the negative is connected to the car chassis for ground.
 

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Discussion Starter · #5 ·
Yes in theory but if anything is connected to the positive - current will flow. When you switch things off you disconnect them from the positive - anything still on will form a cuircit when you connect the battery to ground.
 

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Marcos: The current returning to the battery negative terminal is the same as the current leaving the battery from the positive terminal (it's a circuit after all), so you can measure the current either place; theoretically, it should be the same (but see below about leakage along the battery case). To measure current (as opposed to voltage) you break the connection and bridge the disconnected parts with the meter. Putting the ammeter in series with the ground side is safer, because if you accidentally touch a meter probe or bare connector to some body part, that's a dead short thru the ammeter to ground. Also, don't run anything that uses a lot of power (lights, windows ,starter :eek:, etc.) while doing this - all the current has to go through your meter and can either burn it up or, more likely, blow a fuse inside it.

trackside: Looking at the wiring diagram, the main supply to the ignition switch doesn't go thru the fusebox. There is a distribution point (component #75 in the wiring diagrams) inside the right fender connected to the battery by a heavy wire. The ignition switch is the GY (Grey, I assume) wire connected there. Disconnect that wire (don't forget to disconnect the battery negative first!) and try again. If your leakage stops, you've probably got conductive gunk in the ignition switch as ProfZ suggests in the other thread. Try the other circuits connected there if no luck.

Another possibility (unlikely, but...): repeat your experiment with the battery positive also disconnected. The return (chassis to negative terminal) current should be zero (0, nada, nil, nothing). If you still measure current, there is a conductive path from the battery positive post to chassis - probably some crud on the battery case.

(Even less likely...) There are a few other circuits that don't have fuses, and don't pass through #75. The starter and alternator come to mind.
 

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Discussion Starter · #7 ·
Thanks agin Skip - I did find a thick grey wire that went to the + terminal which when removed caused the reading to drop right down - maybe this is it. I may try blasting the ignition through with some switch cleaner or carb cleaner first.
 

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Ok, what I missed is that the negative had been disconnected, and the meter was put in series with the battery... I know a thing or two about circuitry :cheesy: and have blown my fair share of meters doing bonehead things.

Skip said:
Marcos: The current returning to the battery negative terminal is the same as the current leaving the battery from the positive terminal (it's a circuit after all), so you can measure the current either place; theoretically, it should be the same (but see below about leakage along the battery case). To measure current (as opposed to voltage) you break the connection and bridge the disconnected parts with the meter. Putting the ammeter in series with the ground side is safer,... <snip>
 

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trackside said:
Thanks agin Skip - I did find a thick grey wire that went to the + terminal which when removed caused the reading to drop right down - maybe this is it. I may try blasting the ignition through with some switch cleaner or carb cleaner first.
I'd bet this is your problem--they all do this eventually.

Don't waste your time spraying anything into the switch capsule--it's sealed, anyway--and just buy a new one; they're not expensive (about $35, or 18 pounds sterling, here in the US).
 
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