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You don't need to measure high currents for a battery drain... A shunt is needed when you have tens or hundreds of amps to measure. A draw of that magnitude would make an auto battery useless in an hour.

Any decent multimeter will have a 1a and a 10a ammeter, which is perfect for this application. It's all you need.
 

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Decent but not expensive multimeter:




but this would perform the same function


My Suburban was easy to access, so that's what we'll look at:



First we test on a gross setting - 15a - to see if ANY draw is present.



Since we don't see a big draw, we can test with with a fine setting for better resolution:



Now we know this circuit is drawing 0ma with the car off. Move on to another fuse.

Doesn't take long to do the 20-some-odd fuses in a c900.
 

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Probing fused circuits like that works only if the circuit rating is lower than the current rating of the multimeter. Most standard meters like the one pictures have two fused DC current probe connections but then you are 'replacing' the fuse in the car with the fuse in the meter.

Any circuit rated with anything more than a 10 amp fuse should not really be tested with a multimeter on the 15 amp rated probe connection. IMHO anyway.
 

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I have not read all the posts.
So apologies if I am out of order.

I had a similar issue with my 92 900s vert.

Killed 2 batteries.

In my case it turned out to be a faulty relay under the rear seat.
Same for me and as Jim stated, the interior light relay was the culprit. The relay was warm to the touch after the car was parked overnight in the garage.
 

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Probing fused circuits like that works only if the circuit rating is lower than the current rating of the multimeter. Most standard meters like the one pictures have two fused DC current probe connections but then you are 'replacing' the fuse in the car with the fuse in the meter.

Any circuit rated with anything more than a 10 amp fuse should not really be tested with a multimeter on the 15 amp rated probe connection. IMHO anyway.
Again, a major accessory like a fan would be easy to spot when running, and would kill a battery very quickly. We are looking for SMALL drains, like a light bulb or a relay that is still powered up. Using a multimeter is the correct and proper way to test for parasitic drains.
 

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I'm a little late to the party, but mine was that the brake lights were sticking on. I back up my car by a wall, and only drive on nice days, so just never noticed. Only drained the battery twice until I noticed when washing it one day.
 
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