Something draining batteries. Not alternator. Help?

[makey98]

Well, it got real cold here in Indiana a couple weeks ago. (5 degree low) and my truck wouldn't start. Pulled and charged the batteries and got it to a shop. Batteries tested fine, but alternator was bad. New alternator and everything was good. On the cold mornings it would crank 5-6 times before firing. I checked GRP and it was fine, so I figured I had a couple bad glow plugs but haven't had time to check them. I tried today but I couldn't get the cussed connector off.

Anyway, I had a new baby a couple weeks early so my truck sat for 5 days in about 20 degree weather and then wouldn't start yesterday. It cranked up good, but just wouldn't catch. I had it plugged in all day and it was about 28 degrees today, so it didn't seem likely it was glow plugs. So I charged the batteries again and they tested fine and it started right up.

So something is draining the batteries. I unplugged them tonight and want to know what to look for. Some people talk about a parasitic drain test, but I don't know how to even begin. The previous owner had a trailer brake installed and when I unplug it, it buzzes when i turn the key, so I plugged ti back in and I want to find that and just remove the whole thing. It does have a tiny little led that stays on all the time. He also had some plow connections that I unhooked from the battery completely. My vacuum pump is loud on the Wait to Start, but I am not sure if I just didn't notice it before.

Any ideas? Much appreciated.

[MikeyK]

You sure make me feel warm about transplanting myself from Indiana to Florida 38 years ago ! From what you say I would start with the brake controller, disconnect the 'hot' wire and see if you still have the problem, mine had the Ford Factory installed control and it
would stick on..I believe the led's should cycle off shortly after the key is turned off. Good
luck, hope it is simple, never heard of a parasitic drain test, will have to google it.

[mustang51js]

the way i tested my truck to locate a drain was to get a old light tester, not an led one but one with a old flashlight type of bulb, dissconnect one battery completely and then on the other just disconnect the positive only,take the tester and put one end on the terminal on the battery,(i taped the pointy end to the terminal) then clip the other end to the lug or clip that comes off the battery,the light should be on now, as you start pulling fuses the light will get dimmer as you find something that is making a draw,it takes some time but its a way to pinpoint what fuse is making the draw and then see whats on it,mine actually turned out someone put the wrong relay in so my heat and ac would still run after the truck was shut off

[NoRalPh]

Originally Posted by mustang51js

the way i tested my truck to locate a drain was to get a old light tester, not an led one but one with a old flashlight type of bulb, dissconnect one battery completely and then on the other just disconnect the positive only,take the tester and put one end on the terminal on the battery,(i taped the pointy end to the terminal) then clip the other end to the lug or clip that comes off the battery,the light should be on now, as you start pulling fuses the light will get dimmer as you find something that is making a draw,it takes some time but its a way to pinpoint what fuse is making the draw and then see whats on it,mine actually turned out someone put the wrong relay in so my heat and ac would still run after the truck was shut off

Boy, I'm not sure it's going to be that simple.......

First, the truck ALWAYS has some draw (it's supposed to) and the amount of draw diminishes over a half hour or more!

Your procedure is correct, you should disconnect one battery and test with the other. But, if you use a multi-meter, in the "AMP" mode with current flowing thru the meter, you can see the current getting lower & lower as the minutes pass (mine would peg until the dome light went off )

IIRC after 30mins or so mine was under 150mA when everything is OK. BUT you have to leave it Alone! Close the doors and just walk away and come back

Then, if you Do have a high draw somewhere, you can start to remove some fuses but, remember, there is stuff (pcm / gem at least) that will show a drop in draw when their fuse is pulled, but that could be Only showing you that they were using what they're supposed to....

[MikeyK]

Good method mustang51js, I actually use a battery load tester (HarborFreightElCheapO) from the battery terminal to the battery cable and use it as a DCA tester, but I didn't wanted to keep it simple, and not everyone has or needs one of those, but you have a
good testing method. Long story, short, my daughters 2K mustang did the same thing, very erratic....the problem was the last thing I would have thought of and I was lucky to catch it in the act, the Ford super duper sound system, something which I suspect an amp came on at any given time with the key out, and pull big amps, enough to kill a new battery while she was in school, a real brain teaser to say the least.

[makey98]

Hmmm. This should be fun! I have been disconnecting the batteries when I am done for the night One thing I noticed is that I disconnected the main (passenger side) battery and the brake light controller was still on? This would mean obviously that somehow that thing is connected to secondary battery. Is this normal?

[MikeyK]

The the way the batterys are wired with one disconnected still would keep voltage supply to the system so iyour light would be on.....

[mustang51js]

i forgot to add that i pulled the bulbs out of the dome lights,i know you will allways have some draw but if you pull the bulbs and pull the fuse for the dash lights, i beleive it is #34 and #41 i think, the bulb will go out on the tester if theres no more draw from anything else.if you think the brake controller do what i said with the batteries and tester, pull the fuses for the dash and take dome light bulbs out,if the light is still on then find the fuse for the brake controller and pull that.By the way my brake controller light only goes on when i push the pedal so maybe that is your problem if its on all the time, i would check your trailer plug to in case of ice in it or something like that.I never thought the bulb tester thing would work when my friend told me about it but it did and got me to the fuse that was the problem, then from there i had to get a manual that told me everything the fuse did but its a good starting point

[ozman]

If it wasn't alternator, then I would pull the fuses for the radio. That's where the draw was in my truck last week.

[MikeyK]

My daughters 2k Mustang with the Mach 460 sound system did that and was erratic, would kill a new battery while she was in school, what a complex piece of crap system
that was ..