You connect the amp meter in series, then give the car a half hour or so to fall back asleep. Also, if it wasn’t already said, open up the car doors and and put a clamp over the little buttons so it thinks they’re shut, if that’s possible. Otherwise you won’t be able to get into the car.
Eric The Car Guy has easy to follow video on this. I’m sure ScannerDanner and countless others do as well.
If there is a significant drain and it gets to the point of finding the issue, HumbleMechanic has an interesting way of checking that doesn’t involve pulling fuses and uses a second multimeter. He claims pulling fuses can disrupt modules which can affect other modules (or something like that). His way takes a bit longer, though.
Starts at about 5:27
[quote=“Fantome, post:22, topic:807990”]
If there is a significant drain and it gets to the point of finding the issue, HumbleMechanic has an interesting way of checking that doesn’t involve pulling fuses and uses a second multimeter. He claims pulling fuses can disrupt modules which can affect other modules (or something like that). His way takes a bit longer, though.
Starts at about 5:27
[/QUOTE]I haven’t watched his yet, but I’m sure he’s using the same technique as Eric O (South Main Auto) and Schrodinger’s Box where you do a drop test across the terminals in the fuse box.
The last parasitic drain issue I had was on my old pickup truck. After eliminating everything in the fuse box, making sure there weren’t any sticky relays inside the engine compartment, etc., I began to suspect either the starter or the alternator. The starter had been having issues for quite some time (it was weak and occasionally temperamental), so replacing that was a no-brainer. I probably should have replaced it earlier but it’s an old beater of a truck so I hadn’t bothered. The alternator looked to be in pretty bad shape, and its output was also bit weak, so I replaced it at the same time.
I probably should have done them one at a time just so I knew which one was also causing the parasitic drain issue, but replacing both of them did fix it.
One of these days I’ll get around to fixing the fuel pump check valve in the rear tank and fixing the play in the front suspension. Then maybe I’ll tackle some of the rust on the truck.
I really should just buy a new truck. 
No, either turning on the ignition (with the battery connected) OR reconnecting a disconnected battery will wake up some modules. As soon as you connect the meter, which in essence is reconnecting the battery, things wake up and will then need to proceed through their “awake time” before they go to sleep again. Waiting is meaningless with the battery disconnected. The waiting time only applies when power is connected – the modules need to “time out” under power to go to sleep.
Not quite. There’s no need to “waste no time” for this step. But yes, once the meter is hooked up the waiting time starts.
Even a split second of battery disconnection can allow the modules to wake up upon reconnection. To take advantage of the modules being asleep from the car having been sitting long enough with the ignition off, it’s necessary to keep the battery electrically connected CONSTANTLY through the process of hooking up the meter. If you’re interested in doing that, I’ll post detailed instructions.
In some cases pulling the fuses will not find the problem. In that respect you’ll be looking at the wiring harness for abrasions. This is where the wires had rubbed over time due to vibrations and have their insulation rubbed off and expose the wires to ground or to each other.
I have done many rewire jobs and the majority of them were behind fuse boxes and under the hood. I had some cases of under the dash too.
I must mention that I have been retired from auto mechanics since 2000 so cars have have changed where you’ll find fuse boxes under the hood as well as in the interior.
You have to expect some draw while off. Keeping the ECM and clock up to date for example.
That would be great. Thanks.
What I’ve done is add a battery disconnect switch. Leaving the switch on, I can wait for the car to relax, then put the meter accross the switch, then open the switch - so the current flows through the meter instead of the switch, and the battery is never disconnected.
Actually, I haven’t gotten around to testing that in the last year, because, with the battery switch installed, we just pop the hood and disconnect the battery when it’s going to be parked for a weekor more. But I’ll get around to it real soon now…
Meter [+]lead with a clamp that will fix on neg. cable end securely enough to stay put while being handled and moved.
Meter [-]lead with a probe so the cable end can be lifted off around it. [-]lead ALSO with jumper wire attached, with a clamp that will fit around battery post.
Meter turned on so it completes circuit when attached.
Proceed as follows:
Attach [+]lead to neg. cable end. Loosen cable end so it cab be pulled off later, but don’t accidentally break its contact w/ post.
Touch [-]lead probe to top of neg. post. Keep it in definite contact until clamp below is in place.
Pull neg. cable end off post and attach [-]lead jumper wire clamp to neg. post.
Withdraw probe and set cable aside so it doesn’t touch post.
Read meter!
My Grandson had a drain problem on his car earlier this winter.
Of course he froze his battery with the drain.
I found the problem within 5 min of replacing the battery because of the excessive spark I saw when connecting the new battery and a good one not the cheapie he wanted without my checkbook to help.
Because I had a very similar issue before he was born that caused me 3 batteries before I stumbled on the cause which was the engine compartment light that had been installed backwards after a collision with a deer!
His was a faulty trunk light that did not go out when lid was closed.
Doing this in the dark helps find a like problem.
I found the engine compartment light when I saw the nice frost free circle on engine hood from the upper level of a parking ramp on a frosty (Hoary) night.