Originally Posted by pmckechnie

Rob and 97, I agree with both of you. A clamp on meter is much easier to use but not better in this case. In our shop, we had both a clamp on amp meter and an in series meter. Both had their place. We also had a little box that did exactly what the OP is doing. It also had its place. The two meters cost about $750 each. The little box (that I made) cost less than $5. For intermittent drains, the little box did just fine, and it only needed a DC digital meter which you can not get for less than $20. That would leave the expensive, easy to use meters for checking alternators, starters, etc. In fact, for small drains of 100 miliamps or less, the $25 setup was more accurate.
I have to disagree about the 9 volts damaging the electronics in an automotive application. If it were a problem, then any car/truck with a weak battery would be history the first time the key was turned to start. I agree that some things may not work correctly but that is not what we are working on in this case. The problem with using the 1 ohm resistor in this case is the resistor getting hot and burning your fingers. That is why I put mine in a box and added an inline fuse for the times it was being used when it shouldn't.

Paul