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I know, you say, what are you in business for if you are asking a question like this but this is getting to be frustrating to us because we do alot of electrical diagnosis and repairs.

The vehicle I have right now is a 99 Ford F150 with a 4.6 engine. If this truck is not run for a week, the battery is to weak to crank the engine over. When connecting my dvom and my millivolt meter, the battery voltage can be holding at 12.2 volts and the milliamp draw is 20 milliamps. Well within specs. Next morning I come out, battery is too weak to crank engine over.

What method do you use when a vehicle comes in with an intermittant battery drain? We are getting more vehicles in where the battery goes dead in, say a week or ten days if not used during that time. Obviously there is an issue. My question is, "How do I determine if I have an intermittant battery issue or in fact a drain from one or more electrical sub systems on today's vehicles"? I can look up in On Demand to find the allowable millivolts draw but these intermittants are the challenging ones. I am needing a better way than simply to connect a dvom or a millivolt amp meter an monitor the draw which at the time may be within specs.

I have a snap on DVOM that has internal rechargeable battery and I will hook the meter up with it set to record min/max and let it sit in the extra bay for a few days and see if it ever actually pulls any current. If so then the fun begins, if not then I know it is a battery issue ( unless it is some weird thing like a neighbor car remote waking up your car or something like that )

For the ones that either can not be found or wind up being something cost prohibitive to repair, I have installed a module called battery brain that disconnects the battery when the voltage drops to 11.8. Has a remote to turn it back on without raising the hood. They cost about 100.00 from summit racing and work great. First one I installed was for a late 80s vette with a bad center screen pulling current and could not find one. Three years later and the guy is still very happy with it.

Another issue is when looking for a draw there are relays that require an initial engagement then after a few seconds then reset,. I take a meter and attach one end to post and the other to cable (cable already off of post) touch them together for about 10 seconds then part them. This will eliminate any relays from staying closed. There are also typical issues like door locks and dirty batteries with draws across the top. I've seen 10 volts on occasion. The other thing I run across is if the battery itself isn't 100% it can cause circuit activation killing it.

Speaking of diagnosing electrical drains. Today I have this 2001 Ford F350 with a 7.3L diesel. The issue is that on the start wire (tan with a red stripe) on the starter solenoid, there is 4.2volts at all times, engine running or engine off. The only time there is the normal starting voltage of 12.5 when the engine is being cranked over. The issue is that the starter solenoids do not last very long. A few weeks. Of course, with a steady feed of 4.2 volts at all times even when the engine is not running, it tends to shorten the life of the solenoid. If the ignition switch is unhooked from the wiring harness, the 4.2 volts is still on that wire at the solenoid. And, if I place the transmission in any gear except park or neutral, the 4.2 volts is gone. Where do I look for the problem on this one? Talk about strange - this one takes it to a high level.

I am feeling that I am needing a new strategy for diagnosing electrical problems.

Maybe a sensor ref voltage wire is "shorted". Look at the trans harness for wires rubbed together. Scan trans sensors when cranking to look for a 12 volt signal on a 5 v sensor? I'm thinking a speed sensor circut crossed near the prndl. The 4.2 volts with the switch disconnected is leading me in that direction.