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I own a 2008 M5 and I was just wondering if an approximate 40 amps in additional current is normal when the headlights are turned on

about 60-70 amps in total when the car is turned on... These readings are from the red cable that connects to the battery. The other red cable from the alternator always shows 100-105 amps regardless of battery capacity.

I realize these cars are hogs in this regard but I just wanted to make sure I don’t have any sort of short because even those small cabin lamps on the top and bottoms of doors pull at least 10 amps. Half of those bulbs (especially both trunk lights) get hot enough to burn your hand and melt some of the housing plastic. I replaced one bulb to see — its barely warm now when turned on.

I’m currently trying to diagnose a possible faulty BSD line... as I’m getting a jumpy oil temp gauge reading, IBS communication error, and Alternator communication error code... along with some other DME error codes such 2793 and 278E. I think I’ll check the wires going to the DME and take a look inside of it to make sure it’s 100% fine before replacing anything Just yet. Where is the DME located on my 08 M5? Is it the one in the front hood on passenger side?

Thanks!
 

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40 AMPs seems very excessive, especially since the headlights are HID. Even if they were old school halogens, 40 is alot. I have a clamp meter for my oscope but it'd take me a while to dig that out.
 

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Now it makes me think it be a short in the headlight wiring (from excessive heat etc) ... or bad light module
 

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You can turn stuff on and off or unplug items. If the igniter for the head lamp doesn't cut out that would draw a lot of current. It doesn't seem that bad to me for a BMW. Next time I drive my car I will check and get back to you.
 

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A short would blow a fuse so that's not possible. As I was just updating the cic maps on my car I had the power supply connected. With ign on and all accessories off (no sound from speakers, fan fully off, headlamps off, doors closed) I was seeing about 18A. Headlamps on and there was an extra 10A spike, which settled to about 4A (22A total) after 30sec or so.
 

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Now it makes me think it be a short in the headlight wiring (from excessive heat etc) ... or bad light module
I'm assuming you trust the calibration of your clamp meter to measure the current.

Given the size of the wires supporting the headlamp assy, I don't think it could ever support 40A.

There are a few simple next steps. Unplug one of the headlamp assy's from the harness, what is the current then? Unplug both and remeasure. With just the rears taillamps on, it should be very low draw.
Plug back in the 2st one you unplugged to check the draw on the other side. Doing this can rule out things.
 
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