I've been dealing with an electrical gremlin for the last several months but with the cold weather now upon us, it makes it imperative I find, isolate and fix the problem. I replaced my (admittedly VERY old) batteries about 3 months ago with some NAPA 750 CCA batteries. Everything seemed good to go. My alternator charges at ~14.5 volts and I originally chalked up the occasional weak starts to the old, weak batteries.

Well, now it's cold and--after sitting for 2 days--my truck was dead as a doornail. I jumped it again ( thought I'd gotten rid of this problem!) and drove it for a few more days. Then, it sat over the weekend and BAM, I had to jump it again this morning. I'm not interested in ruining a brand new set of batteries so I've got to find the problem.

I measured the amp draw between the driver side negative cable and terminal with the battery disconnected and it ranged anywhere from 28-42 milliamps, and never really changed even when I disconnected every gad dang fuse both under the hood and in the cab.

Then, just for kicks, I disconnected BOTH negative cables (because I noticed that the cab light was still on with the D/S battery disconnected). I put the ammeter on the D/S cable and terminal and immediately measured a 180+ milliamp pulsing draw with clicking coming from inside the cab. But, it killed my 200 milliamp fuse so I was left with my test light. With the test light connected, I traced the clicking to a little black box under the dash to the right of the steering column (BCM?) and also discovered that the clicking stopped and the pulsing test light stayed lit without flickering when I opened the glove box so the glove box switch was tripped. As soon as I pressed the plunger the clicking and flickering started back up.

Have I found my parasitic draw? Am I dealing with a glove box light problem drawing ~200 milliamps all night long for a couple nights? Can I just disconnect the thing? I don't need the light anyway.

 

I'd dang sure disconnect the glove box light. Not sure if the clicking black box you are talking about is a bad relay, but I'd definitely disconnect the light.

 

Well if gb light goes out when close door, it is not the issue.
As you found out, you must disconnet both batteries for amp draw test. Everything must time out with doors closed. .2 amps are to much draw. Do you have a FSM. Life is easier with such.
.04 amps draw seem normal. Computer keep alive circuits involved.

 

Didn't the 1999 have electric locks on the seatbelts? Powered to release I think for a timed period, so maybe one is staying powered. The module that controls them is under the dash in the center I think. Maybe someone else can chip in.

 

The CTM always draws power. 200 ma is just 1/5th of an amp/hour. It takes 5 hours to consume 1 amp/hour. Your batteries are capable of several hundreds of amp/hours each and you have two of them. Look elsewhere for your problem..

 

No, unfortunately I do not have an FSM for this truck. Are they published in multiple volumes? Are they available as a .pdf from anybody?

So far, I've had good luck by keeping the truck plugged in overnight (with overnight lows only in the high 30's to lower 40's) and the truck starts right up even though it sat from Friday morning through this morning.

Anyway, I thought about my glove box. I still don't know why I'm getting a pulsing draw with the glove box door closed but, after thinking about it, it hit me that of COURSE I'd have a steady draw with the glovebox open. The circuit turning the light on would be complete! So, there's really no mystery there why my test light lit up solidly; the mystery still remains, though, about why there's a draw with the glovebox closed and it's not constant but rapidly cycles on and off.