I posted yesterday about dealing with a parasitic drain on my '06 F350, but I have run into a new issue this morning.
I’ve been measuring an amperage drain of 1.76 (I’ve already tested all the fuses, relays, stereo, cluster, and alternator). I still need to check the starter, GPCM, and the alarm.
I left my batteries disconnected overnight and checked them this morning; they were fully charged at 12.7 volts. When I reconnected them, they immediately dropped to 12.5, and the truck struggled to start. After it started, I checked again, and the batteries were at 12 volts.
I let it run for a bit, and the batteries rose to 14.5 volts, which is normal, so the alternator is functioning properly. I also tested the diodes and did an alternator test yesterday, and everything was fine.
Do you have any advice on why the batteries dropped so dramatically?
A circuit must still be reaching ground. Does a positive battery cause aftermarket items to come off? You disconnected the batteries entirely, ruling them out. Overnight, bad batteries will quickly drain. Look for anything that is still fused, or worse, unfused and moving toward the ground.
Yes, I have left the batteries overnight on several occasions, and each time they maintained their charge.
I unplugged the power cable that goes to the car stereo amplifier even though there isn’t one there to check.
This morning, I checked the gpcm and starter, and the amperage draw remained the same.
I unplugged everything that was on the alarm, but I am not sure if I actually did it, and it still has the same appeal. It’s conceivable that I left some of the alarm components operational because I’m not the best with electricity.
There are two main fuse panels, the battery junction box (BJB) under the hood and the central junction box (CJB) inside the cab. One fuse in the BJB provides all the power to the CJB, so start by checking that fuse. If the draw remains unchanged, the issue is likely from the BJB, which eliminates half the vehicle’s systems. Then, remove fuses one at a time from the box that is still drawing power until you identify the faulty one.
Therefore, if the truck had trouble starting and the batteries were at 12.5 volts, and your engine is running OK, you either have a bad starter, a bad motor to chassis ground, a bad starter, a voltage drop in the wiring to the starter, or bad batteries.
I would start by addressing those problems, and perhaps you will discover your parasitic attraction in the process.
Get a wiring diagram and test each circuit that isn’t going through your fuses or relays if you still don’t.
Running jumper wires (both + and -) to the starter is a simple method of ruling it out. I normally begin the diagnosis that way.
Check out the South Main Auto channel on YouTube, he’s an expert at diagnosing parasitic draws and other wiring issues. You should use either an ammeter between the batteries and the vehicle’s electrical system or a sensitive voltmeter to measure small voltage drops across fuses, which can help identify current flowing through that circuit.
Also, note that the Central Junction Block (CJB) under the dashboard is a large fuse and relay panel that contains a circuit board with at least five soldered relays for components like the fuel pump and horn. This isn’t clearly explained in the factory wiring information, so you’ll need to do some digging to uncover it. If one of these relays is stuck in the “on” position, it could cause a draw. While this is unlikely, I wanted to mention it since many people don’t realize that those relays are hidden inside the CJB and are soldered in place, making them difficult to replace without spending hours desoldering a large pin header to access the back of the circuit boards.