dme

(WITH THE ENGINE OFF) - Using a DC AMP meter, I pull the Negative terminal off of the battery, put the positive (red) probe on the negative cable and the Negative (black) probe on the negative terminal, Begin with the highest setting on the meter (usually 10 amps) and work down till you are in the proper range.

bearone

with the neg cable removed isn't it an incomplete circuit with no draw of current?

KuHL 951

The ammeter completes the circuit; personally I use a shunt to protect my multimeter from high current 'surprises'

dme

If your getting better then 10 amps draw with everything off then there is a real problem.

M758

On the 85.5 and later cars the door switch controls the window relay. When you shut off the car the window relay stays active unit you open the driver's door. If the door switch does not work then the relay stays active and will drain the battery in a little over a week. I had this problem on my 951.

bearone

now that does make sense. thanks.

bearone

would it be valid to check the switch with the lite when the door opens?

KuHL 951

If I suspect there is a major drain from a failing accessory or possible short it's better to have a means to safely measure current greater than 10A from each circuit. I sometimes need to do this with the engine on as well as engine off. All of my multimeters are fused on the ammeter circuit but many less expensive meters are not. Calibrated shunts (1A, 5A, 25A, and 100A) are just a safer method I prefer to use, that's all.

faithless

Always make sure to follow the directions on how to read current as stated. Reading current is NOT the same as reading voltage. If you try to read current the same as you read voltage, you'll either create big sparks and scare the **** out of you, or you'll fry the meter, or who knows what else.

Highway T

Perfect timing - I need to check mine.

I just had an immobiliser fitted (damned UK insurance companies!) and it flattened my battery within a week. Prior to that it would sit 3-4 weeks and start without hesitation (battery now 18 months old).

They definitely mucked up the wiring as the courtesy light does not come on when the drivers door opens. It goes back to the shop on Wednesday so wish me luck.

I understand the difference between measuring current and voltage but please describe a shunt. Is it something you buy or lash together?

Chris

Zero10

It's a low value resistor, that you put in place of an ammeter. You measure the voltage across the shunt to determine the current passsing through it

Highway T

Doh

Got it, thanks.

Chris

Matt Marks

Take keys out of the ignition.

Ttake the negative wire off the battery. Connect your ammeter in series from the battery cable to the negative post on the battery. Make sure you have your meter set to the appropriate scale or you'll blow out the meter and/or the fuses.

To check for current draw circuit by circuit, open the fuse box and place your ammeter where it's readable. Run a test lead (wire with clamps on both ends) from the negative terminal of the battery accross the car and clip it to the positive lead of your ammeter. then, run another lead from the negative lead of your ammeter to back to the battery cable.

Then, pull fuses one by one and see when the current draw goes down. The pulled fuse that reduces the current draw indicates which circuit is pulling the current.

Looking up which fuse the circuit is for can give you an idea of what to troubleshoot for shorts, etc. in my case, it was fuse 39, which is the radio.

You would then need to start working your way through the wiring harness, etc. to see where a short is or what is causing the current draw.

M758

Yep... That is of course assuming you light works.