Parasitic Battery Drain!

[L1011tristar17]

Hello everybody. I drive a 1989 Town Car and for the first year and a half I've owned it, I've had virtually no electrical problems. Some of the wiring looked shady as best but most of the power accessories seemed to work. About a month ago, I went to start my car and the battery was completely dead. I thought nothing of it, as I hadn't driven in a few days, jumped it, drove for about an hour, and parked it.

The very next day, the battery was dead. Very dead. About .6 volts were left in the battery. I got it jumped again but I knew the battery was probably damaged. Since the battery was almost three years old, I went ahead and replaced it, and disconnected the power seat motor on the passenger's side, which I believed was causing the drain. Three days later, car's dead again. Still can't locate the drain since I don't own a multimeter. I eventually took it to a shop who looked at it and apparently fixed it while the old alternator was being replaced (it had bad bearings.)

Since then I have had to jump-start my car numerous times, which is downright embarrassing when in front of my car-savvy friends or other college students. The last time it died I swore I had disconnected a wire that was draining 0.9amps. I even cross-checked it with wiring diagrams. Checked fuses. Checked grounds. Checked battery and alternator.

TL;DR car keeps dying and I can't find the source. Every time I think I fix it the car's dead the next day.

Does anyone have any insight as to what could be draining so much power? Both the alternator and the battery are A-OK. I usually borrow a multimeter from a friend but I don't have a bunch of diagnostic tools (I do have a code scanner and the electrical diagrams.) Any help would be appreciated!

[GoodSamaritan]

Here's a quick and easy troubleshooting tip. Get a taillight bulb or something similar along with a socket and the wiring. Charge your battery up. Remove one of the battery cables, and wire the bulb up between the battery terminal, and the cable. (in series) The bulb should light up. Give it a minute to charge up any capacitors in the ecm/stereo etc. Now start disconnecting things/ pulling fuses one at a time till the bulb goes out.

Make sure your doors are closed or else the load from the dome + courtesy lights will confuse the issue.

[sly]

as a quick check... make sure the trunk and hood lights actually go out before either is completely closed. If not, that may be the culprit and a little bending of the mounting bracket may be in order to get them to go out when they're supposed to.

I had this problem with my Lincoln when I first got it with the hood light.

[GM_Guy]

1. Go buy a voltmeter.
2. Measure voltage at the battery to make sure its getting proper charge voltage.
3. Measure actual current draw (car off).
4. Report back with your findings.

Alex.

[86VickyLX]

I had this happen where after the car was turned off the alternator was sucking up power through the rectifier. Car sat all night and the alternator was super hot.

[85crownHPP]

Just because an alternator is charging, that doesn't mean it's 100% ok. Mine charged great but would drain the battery when parked in half a day... you could have gotten a bad one.

You mentioned 0.9 amps... does this mean you bought a meter? Are you reading a draw now?

[L1011tristar17]

Thanks everybody for the advice! I haven't gotten the chance to check the drain in a few days and have just left the battery cables undone whenever I parked it. I don't own a voltmeter but that's definitely something I'm looking for. I've been borrowing one from a friend and it seems to work pretty well.

Last time I got the battery checked (a few days ago) at the local O-Reilly's and again at an auto shop, the battery seemed to receive about 13.5-14 volts from the alternator. I double-checked this later with the voltmeter and it seemed correct. When the car was off, there was a 0.9amp drain from the battery. I was positive (no pun intended) that I disconnected the one wire that was causing the drain, but something is still zapping the power. That's what I'll be checking from tomorrow and I'll probably start with the alternator.

I'll also use a test light this time. The voltmeter I've been using is one with the claws that go around the wire (without touching it) and read the amperage. I don't know exactly how reliable those are.

[sly]

to see if it's the alternator that causing the drain... disconnect the charge cable from the starter solenoid on the fender (disconnect the battery first of course) as well as the connector harness on the alternator. If the draw goes away, what 86VickyLX said is probably the case and the alternator needs to be replaced/rebuilt.

[meandad]

A heavy kind of drain like that could be caused by the alternator as Slymer suggested, or the famous bad rear defroster switch. the rear defrost pulls a lot of juice if the switch goes bad. If you see like a 15 Amp draw, thats your guy. Just disconnect it in the trunk temporarily. Usually you can see the little light is still on next to the switch after you turn the key off.

[L1011tristar17]

I checked on the car today while borrowing my friend's multimeter. I can't say I really trust the accuracy of it, since it's one of the really fancy ones and I have no idea if I'm using it right! I did notice however that the wire that's really draining the power leads to the alternator and a bunch of other misc. accessories through the fuse box. (So much for narrowing it down!) The alternator didn't seem to be the problem since I unplugged it (as well as the regulator) and the drain seemed to remain the same. I think I'm going to give in and take it to a good autoshop that I trust. There's a bunch of other wiring issues (frayed wires, loose connectors) that I don't have the tools or time to play around with.

I must say that I'm glad I found this site! I can say that I learned a lot just by reading the threads around here. Hopefully as I become more experienced I can do some more of these mods myself (the 3g alternator upgrade looks really interesting, potentially a summer project for me)

[Lincolnmania]

mine did that, it was a bad defroster switch

[GM_Guy]

Since you have a dvm at your disposal,
Yank out the hood light before it gets hot.
Disconnect the negative battery cable, set the dvm to at least a 10amp setting, hook the dvm in series (one lead to the battery cable, the other to the negative post on the battery), read your drain. Pull one fuse. Note the amp reading. Pull another. And another, and another, until you find the one that is significantly drawing. Put your fuses back after you check. I don't want your next post to be "I have a handfull of fuses, where do they go" =-) Once you establigh the high current reading you can set the dvm to the next highest amp setting so you have better resolution.

Normal current draw (with stock radio) is under 100mA (at least it was in my car). Make sure you close the door when you read the current, or remove any interior lights that are on (dome lamp, doors, floor).
If you have a trunk light, take note of the reading, remove it. Check reading again. DO the same for the glove box light. Check readings. You may be done if things are normal after pulling the extra lights.
If it ain;t, find the defroster fusable link (or disconnect the wires from the defrost switch if its easier) and check your current draw again (you'll need to pull the defroster fuse as well).
Start with the easy stuff (hood, trunk, glove box light, one by one).

Alex.

[gadget73]

yeah, I had a bad defrost switch too. try clicking it off and see if it changes. Mine had failed in such a way that it didn't shut itself off properly, but it was OK as long as I manually threw the switch.

[GM_Guy]

disconnect wires at defrost switch should read: disconnect the switch connector.
And replace the fuses when your done: pull one, check, reinstall it. check again. go to the next fuse.

From the sound of it, my turfing the rear defroster in the process of project rotary control may have been proactive maintanence.

Alex.

[L1011tristar17]

Thanks for all the help everyone! After spending nearly three weeks trying to diagnose this problem, I just sent it to the autoshop I go to for them to diagnose. I'm also going to get some connectors replaced that look pretty corroded and ready to start a fire. My friend's ammeter was one of those weird clamp-ons that neither I nor him could get to work properly. I would get one reading, my arm would move slightly, and the reading would change dramatically! I think I'm going to save my pennies and get one with leads instead. While I'm trying to get a cheaper one, are there any brands that are good/that I should stay away from? I do believe I have a large one (from the late 70's) but I just can't get it to work. Oh well, that'll have to wait.