I couldn't keep the battery charged, but when I tested with a voltmeter while it was running, the alternator was putting out 13 or 14 volts. I thought that would be enough to keep the battery charged, so I figured that it must be a bad battery and I replaced it. The replacement ran the truck for awhile, but now it's dead too and the truck won't start. So obviously I'm still not keeping the battery charged. I cleaned the connectors and I took all the wires out and put them back to try to make sure they were making a good contact. I'm not sure what else to test?

 

Parasitic drain, is where I would look next. Your multimeter probably has a 200ma and a 10amp scale. Set to 10amps, firmly attach the lead to the battery post and the battery cable (either side okay, but it is always safer to remove the negative/ground side first). Then disconnect the cable so that the meter is bridging the battery post to the cable. If you get 0.2 or more, congratulations! By starting with the 10amp scale you avoided damaging the meter. 200ma is high, but not so high that it should run down a battery.

Don't forget that an ammeter is a dead short. If you put the leads from + to ground, it will blow the meter fuse or worse.

Last, in my neck of the woods, auto parts stores will test a battery for free (on a fancy type of carbon pile tester). You don't need to replace it without testing. But if your battery was over 5 years old, you didn't hurt anything by getting a new one.

 

With nothing on, I get 0.020 amp like Scope mentions^^
Illustrated:
https://www.yotatech.com/forums/f116.../#post52431770

 

Thank you for the reply, I think you're on the right track here. When I tested it like this it spiked at 0.08 to 0.09, but usually settled at 0.02 and stopped moving as long as I wasn't moving the connectors (I have one of those cheap Harbor Freight digital multimeters that don't have clamps). It seems difficult to test if it doesn't give me a consistent number, but I'll give it a shot and see if I can get it to stop spiking at 0.08 when I first touch the connectors. I pulled the radio fuse which is where I suspected the problem would be, but it still did the same spiking. I will try a few other fuses and see if stops doing that so I can try to narrow it down.

 

Any other non-factory items installed like alarm, audio amp, etc...?

 

There wasn’t a cigarette lighter installed so I added that to be able to charge my cell phone.

My windshield washer fluid pump wouldn’t turn on from the steering wheel lever anymore so I hot wired a button to turn it on whenever I pressed the button. It’s getting its power from the washer fluid fuse.

I pulled both of those fuses and the multimeter didn’t change. It keeps settling on 18.4 milliamps. I switched to the 200ma setting since it wasn’t going above .2 amps so I could get a more accurate reading.

Each time I touch the connectors, it starts at 40-something, switches between say 45 to 48 to 46. Then jumps to 89 or 88. Then goes to 91. Then back to 88. Then back to 45. Then settles at 18.4 and stops moving. I’m not sure if that’s normal for a cheap multimeter, but it’s consistent each time. All these jumps happen in under 10 seconds, and then settles at the 18.4 number.

Pictured is my redneck engineered windshield wash button wire.

 

Disconnect alt to batt wire from alt stud terminal. (B)
Measure resistance from stud to ground. U.shud get very high resistance. almost open. Lots of megohns. Sorry forgot exactly what measured on mine that works normally.

 

I wasn’t sure what resistance setting to put the multimeter at, but with the knob at 200k, I got a reading of 37.3 when going from the the disconnected alternator stud to ground.

Here is the setting on the multimeter.

 

Since I couldn't remember the reading before, I checked the voltage again while the truck is running and it was 14.59 or 14.60 at the battery terminals. I turned on the heater full blast and the headlights, and it dropped to 14.35

That should still be enough to charge the battery though, shouldn't it?

The radio has stopped working recently, which is what led me to believe that there might be a short or something causing a drain from the radio, but the battery issue has been happening for longer than the radio hasn't been working, so I don't know if they are related. Since I pulled the radio fuse and got no different reading, I guess probably not related.

 

The spike you see is pretty normal activity, this is "inrush current" where things like capacitors charge up and choke coils go from being "just a wire" to a choke and such..

You can eliminate the variables by putting a set of alligator clamps on to your probe leads, they are less than a dollar, just crimp the alligator crimps down to a friction fit on the probe tips and slip then on and off as needed. (Some meters actually come with these in a rubber coated pretty package, they are also available by themselves or as a package with leads..)

Have you popped the vents off the battery and topped it off with distilled water? How old is your battery? Are you measuring that 14.6 v at the battery post or on the battery cable terminals?

What kind of stereo do you have, and how is it wired? This is important because digital radios tend to have a constant connection to power for things like channel presets and clocks. Just because it doesn't turn on doesn't mean it won't be pulling power..

Based on your alternator voltage underload I suspect your battery either isn't getting the juice or not storing it properly. Make sure it's topped off with liquid and drop it off at your local Wal-Mart for "testing" it will either come off in ~20min as dead/good (& freshly charged!) Or there machine will run a recovery(desulfurization) cycle on it then try one more time to charge and load test it. You'll get a printout of its voltage an amp output.