Just went outside and the truck won't start. Jumped it off, so it's not the battery. Hooked a test meter to it and sure enough, with the battery disconnected it's trying to pull 12 volts. Background.... I was rearended a few weeks ago and had it repaired. I just put some new wheels on, so the TPMS light is on. Any of this cause a drain?

 

Not sure I'd let the battery off the hook so easily - a good jar or bump could have caused some internal damage.

With your test meter - hook it up to measure amps. Unhook one terminal of the battery, leave the other terminal connected, and put the meter in-line between the cable and vacant battery post. If you're getting more than 0.2-0.3 amps with the truck and accessories shut down, then suggest you have excessive current draw.

 

how old is the battery? More than 4 years... replace it.

Is the battery wet? Damp? you can get parasitic loss between terminals from moisture conducting electricity.

All cables clean and tight at both ends?

The truck is always using power, get a amp meter and put it in series with the + cable with the truck at rest and see what the draw is.

Let us know how many amps you are drawing. It shouldn't be a half an amp IMHO

 

It's an 08 truck, so less than two years on the battery. I put a voltmeter inbetween on the negative side an I get 12.02 volts.

 

OK - understandable and a valid reading - but we're after amps, not volts.

A voltmeter will present a high-impedence / resistance across the test leads, likely on the order of several thousands, if not millions, of ohms. This is intended so that the measurement does not affect, or draw down, the true voltage between measured points, as well as to protect the meter. A voltmeter is typically applied so that it is in parallel with the load being measured.

An ammeter presents a very low impedence or resistance, likely on the order of thousandths of an ohm, or less. Again, this is intended so that the meter does not present significant resistance that would affect the true current flow in the circuit. There will likely be fuses in the meter to limit the amount of current allowed to flow through the meter, typically somewhere between 1 and 20 amps - depending on the meter. An ammeter (barring the clamp-on styles) must be applied so that it is in series with the load being measured.

Some meters cannot measure amps, only volts. Those that can measure both typically have a separate connection point for the test lead, due to the differences of meter impedence for each measurement. If this is the case, it will likely have a COM point, an A point, and a V/ohm point. The lead on the V/ohm point will need to be moved to the A point, and the selector dial moved to the amps section.

Be sure to move the lead back before trying to measure volts again. I've popped many a meter fuse when I forgot.

 

Okay, did what you said and got -0.37.

 

Hmmm, OK. Suggest that my memory is old school, and perhaps 0.37 amps is not excessive for the newer vehicles with all the additional computers, theft deterrents, and other features that will have some power draw.

Suggest at that draw, a battery in good shape should still be able to light things off after a week of sitting.

Have you considered pulling the battery and getting it load-tested?

 

You first sentence confuses me; if the truck would not start until it was jumped from another battery, then indeed you do have a bad battery, or something draining it. To test something draining a battery, connect an amp meter between the positive cable and the batteries positive post (and don't have any door open, don't start the truck). If you see any reading on the amp meter, something is drawing off of the battery. You can then remove one fuse at a time until the amp meter shows zero. You'll now know what circuit(s) is creating the draw by checking the owners manual as to what is assigned to that fuse.

I'd also check any wiring harnesses at or around the area you were rearended and had repair done to. Could be that you have a chafed wire that's touching ground, but it should have blown a fuse...

 

have the battery load tested.. if ok then load test it.... latch the passenger door latch so the door light is out using a amp meter on a 100 amp scale connect the leads on the negitive post and the negitive cable the truck needs to sit aleast 45 mins for the modules to go to sleep you will expect to see somewhere aroung 60milliamps at first as modules gor to sleep it will drop a good reading is less then 20 milliamps anything hight there is a draw that is why we left the door latch rolled up get in there and pull fuses until the draw drops that will be your circuit then you need to find what is on that circuit... repair as needed..

I think you'll find the battery at fault.. haven't seen to many draws on F-series

 

With everything off, it still gets 11.8 volts. I will take the battery in tomorrow. It is defiantly draining from somewhere. I spent an hour looking for fuses today with no results.