AggieJustin

I've been trying to track down a key off battery drain that has been pulling down my batteries. In early December, the truck sat for about a week and half and when I went to start it, the battery voltage was right at 8 and the grids killed it. I jumped it off and things have been OK, but it seems that if it sits for a few days my battery voltage is down when I first turn hit the key (lower than normal, even accounting for the grid heaters being on).

My multimeter has a blown fuse, so I wasn't able to get specific amp readings, but I used a test light to check draw. I isolated the main battery on the drivers side, pulled the negative and put the test light between the clamp and the post. The light was burning pretty bright and steady (almost full intensity). I disabled the hood light which dimmed the test light slightly, but it started a very rapid pulsing. I didn't find anything in the PDC under the hood, so I moved into the cab.

I first removed fuse #13 which cut power to the CTM and disabled the interior lights. That didn't show any change in the bulb brightness. I pulled the other fuses I traced the main source of draw to fuse #14 (Cluster B), which is supposed to provide battery power to the cluster even with the key off. When I pulled fuse #14, the test light went out completely.

So how many amps should this circuit be pulling with the key off? I'm going to get a new fuse for my multimeter and check the actual number of amps being pulled. But based on the test light, it looks like it's a pretty significant draw.

WestTN

That is the Ignition Off Draw fuse I believe. Did it have a little black retainer clip on it? If so, it keeps the time and station presets in memory and shuts many other things off as well. I seem to recall this cirduit drwas about 195ma. It was put there do kill power loss from the battery during strorage.

AggieJustin

No, the IOD fuse was #12. When I pulled it, it didn't change the intensity of the light. Since the light went out when I pulled the #14 fuse (while the IOD was still in), I'm guessing the IOD fuse draw is so small that it doesn't register on the light.

Also, for the record, I did leave the light hooked up with the doors closed for about 30 minutes and there was no change. So it wasn't something controlled by a timer that shuts off shortly after the truck is shut down.

nickg

I think there was a post or two about seatbelt locks that drain the batteys, a simple test was to leave the window down then after a period of time(1/2hr maybe??) reach in and see if the seat belts were "locked" or if they pull out, if they still pull out easily, there is a seatbelt issue

something else to check

AggieJustin

I'll have to try the seatbelts again today. That was part of the reason for letting it sit for a half hour last night to see if anything would turn off. But I'll need to actually try the belts to see if they lock up.

I did try unplugging the seat harness under the driver's seat last night, but that showed no change on the light. I just realized that I didn't check for a separate harness under the passenger seat though.

So should the seat belts lock if you pull both batteries and cut off the power supply? Or are they fed by a capacitor that still has to drain? I've looked in the wiring diagrams, but I can find anything about the seat belt retractor. All I can find related to seat belts is the seat belt switch for the driver side that shows whether or not the belt is buckled.

AggieJustin

So it's not the seatbelts. The '99s were the last year model to use the electrically controlled solenoid to lock the belts. The later year models went back to the standard ratcheting lock.

So I'm back to square one with needing to get an amp reading to verify how much power is being drawn through that fuse and what is on the other end pulling the power.

dodgeguy71

Replace your fuse in your ampmeter and retest, disconnect ground, put your meter inline, milliamps. Don't use a test light. It tells you there is a draw, all modern cars have a draw for the most part. So really gives no indication other than the fact that, yep, it has a draw. You need to know how much and then you can start to narrow it down with a schematic based on what is on that particular circuit(fuse 8 powers....XX, XXX and XXXX, follow me?) Then you can go around and unplug each of these one at a time and watch your meter. I forget what the figure was for the GM's but seems like you could divide your battery reserve, i.e 120 minutes by 4 and that would tell you your max draw in mamps, which is 30. Now, at the caddy dealer I don't think they wanted anymore than 20mAmp draw. If you have less than that I'd vote for bad batteries and not a draw, but you need to know the actual numbers.

A little tip, I bought an inline fuse holder from the zone, put a 10 amp fuse in it and kept spares in the box that held my meter. I would put that 10 amp inline with my meter, that way when I got vehicles with mega draws on them it would pop the CHEAP inline fuse instead of the $5 Matco fuse inside my meter.

Chasing a draw was interesting, I've had interiors of cars gutted, trunk mats pulled up all sorts of stuff. We had an escalade with a draw one time, long story short, after chasing it for awhile we found this odd box buried behind the interior moldings in the cargo area. Come to find out they were going through a nasty divorse, the wife had a PI put a tracking devise on the husbands escalade. Our shop foreman called him and asked what he wanted us to do(was killing his battery in a couple days time). The husband said, "disconnect it but leave it in there". So we killed the power to it and sent him on his way. We laughed about it cause we hoped the PI was watching his location on his laptop somewhere, the little, blip, blip and then gone!! Ahhhhh, gave us a good laugh. Then I went and filled out my time for warranty from GM, got screwed as usual.

AggieJustin

I think this mystery may be solved.

I picked up new fuses for the multimeter (along with the inline holder for insurance - thanks dodgeguy71). I isolated the driver's side battery again and put the meter in series.

With the hood light disabled, I was reading 1.58-1.62A with the interior lights on. When I pulled the fuse #12 to kill the power for interior lights (and the CTM), the draw dropped to 0.10-0.11A. I switched over to the mA scale and saw 108-112mA. I've done the power window mod where you cross the wires from the power seat to the power windows (so you have power windows full time and power seats with the key), but this keeps the little ID lights on the door switches powered. When I pulled the wire feeding the power windows, my draw dropped to 3.2mA. If I pulled the IOD fuse, I'd come down to 1.5mA.

When I pulled fuse #14 (Cluster B), I saw no drop in the draw. But I did notice that when I plugged that fuse back in, there was a brief spike in the reading. So there must be a cap or something in the cluster that gets charged up. I'm guessing that test light wasn't carrying enough current to initially power up whatever was on that circuit, which is why the test light would pulse. Today the readings are rock solid.

So it looks like I was chasing a ghost caused by using the test light. Lesson learned.

Also looks like I need to reverse my power window mod (or find a way to disable the ID lights). With the mod in place, my draw is 114.5ma. Without it, I only have 7.6ma. Hard to believe those little lights increase it that much.

As for the starting issue, turns out I did have a bad battery. My passenger side wouldn't hold a charge under load. I put the tester on it and it pulled down to around 5V under load. If you charged it, it would do fine for about 15 seconds, then it would drop like a rock. Free replacement at AZ after they tested it and saw the same. The other battery tested OK, so AZ wouldn't replace both.

Thanks to everyone for the help. Glad the answer was something cheap to fix (this time).