Electrical MYSTERY? Blower motor runs when key is off

[mtnmankev]

Good thinking, but the battery is from 2020 and still healthy to my knowledge. It recharged fine and has held >12V while disconnected. The battery tray might be a little crusty, but it's complete with a functioning hold down. I don't think it's bad enough to cause this.

The draw killed the 2020 battery, as well as the battery from my Monte Carlo that I swapped into it. Same overnight drain. The wiring in the truck is relatively unmolested. I'm thinking it has to be the alternator, and I'm just doing something wrong with my DMM and can't pick it up.

Here's an idea, crude but effective.
If you have a spare 12 volt single filament bulb laying around, take a chunk of small gauge wire, strip an inch of insulation from both ends.
Hold one end of bare wire to the brass part of the bulb with one hand, and hold the lead contact on the bottom to the battery post.
Touch the other end of the wire to the cable end.
It functions as a test light, might call it redneck style, but does the job.
Or, if you're lucky enough to have a spare 12v light socket with the wires attached, it's easy enough to make a test light from it.

 

[Radiohead]

Don't laugh. I used a 194 bulb with the contacts bent away from the glass as a redneck noid light on the fuel injectors of a Nissan hardbody. Worked flawlessly.

 

[SirRobyn0]

Don't laugh. I used a 194 bulb with the contacts bent away from the glass as a redneck noid light on the fuel injectors of a Nissan hardbody. Worked flawlessly.

Don't laugh, I got sick of buying new noid lights because someone (including myself) broke one, or lost one. I have a 194 with staples straighten out and soldered to the wires from the bulb. Works great and is flexible for most needs. When it breaks or gets lost, it's no big deal, because I don't have to get raped by one of the tool guys because I need it now and can't drive to a HF.

 

[scrap--metal]

Here's an idea, crude but effective.
If you have a spare 12 volt single filament bulb laying around, take a chunk of small gauge wire, strip an inch of insulation from both ends.

Don't laugh. I used a 194 bulb with the contacts bent away from the glass as a redneck noid light on the fuel injectors of a Nissan hardbody. Worked flawlessly.

I have a 194 with staples straighten out and soldered to the wires from the bulb. Works great and is flexible for most needs.

Thanks for the ideas, guys. Sounds like I should hop on this bandwagon. It's totally my style, especially staples soldered to the bulb. LOL. It may be a moot point though, at least for this troubleshooting.

 

[scrap--metal]

With the alternator unplugged, my battery held a charge overnight. No more draw.

So, I'd like to fix the alternator instead of replacing it. I haven't opened one up in over a decade though.

Is this the "diode" that causes a draw in an alternator? I should note that I have a 10SI in there instead of the factory 12SI.

You must be registered for see images attach

 

[Snoots]

Several folks have the right idea. To find the draining circuit, take a bulb with wires attached and remove eash fuse one-by-one. Connect your bulb across the fuse contacts. If the bulb glows, you've found the circuit that causing the drain.

 

[mtnmankev]

With the alternator unplugged, my battery held a charge overnight. No more draw.

So, I'd like to fix the alternator instead of replacing it. I haven't opened one up in over a decade though.

Is this the "diode" that causes a draw in an alternator? I should note that I have a 10SI in there instead of the factory 12SI.

You must be registered for see images attach

That's the diode, but it's a smart idea while you have it apart to install a new regulator and bearings.

 

[greyghost]

back to first post factory radio shud turn off when key switch turned to OFF , if it stays ons theres parasitic draw, turn radio off, dome light, shut door, turn key OFF , pull fuses one at time, start with horn, drain batt? if no horn button stuck on n horn needs replaced, lights, brake lights,

 

[scrap--metal]

So after some more DMM testing, my battery drain wasn't cased by the diode trio pictured in post #20. Instead, it was one of the positive diodes in the rectifier. Since that diode is soldered to a heat sink and didn't come in the parts kit I had, I did a parts swap with another 10SI alternator I had.

That spare alternator had a bad voltage regulator that overcharged sometimes. I put the voltage regulator from my K10 alternator in the spare, and now it's working great. My truck is happy again (no battery draw) and I have one serious core of an alternator. It's got an overcharging voltage regulator, a bad diode in the rectifier, a bad spot in the bearing, and two badly worn brushes.

 

[muppett]

We saw a rash of bad reman alternators doing that in the dealership years ago. We would charge up batteries and use infrared temp gun to see what was staying on to cause draws. The alternators draw a lot and were pretty obvious when checked after a few hours.

 

[scrap--metal]

The alternators draw a lot and were pretty obvious when checked after a few hours.

Mine draw was obvious as well. After a couple hours, the battery voltage would be noticeably lower when checked with a DMM. Overnight it'd be down to 3-ish volts from a full charge the evening before. Not good for my battery, but it only drained down that bad once or twice.

 

[Ricko1966]

O.P. has found his problem here's a quick and easy diode test. For those that don't know it.Multimeter on AC volts, check for AC current from alternator positive to ground with engine running about 2000rpm you shouldn't have more than. .5v AC current. Engine off, remove the positive alternator lead,check for voltage draw between alternator positive post and alternator positive lead,you don't want more than a couple of milliamps.
A.C. voltage can cause drivabilty problems and false codes too.