Hello. I have a 2003 Ranger. Many years ago, I replaced the stock stereo with a cheap after-market one. It was cheap, but still an improvement, bluetooth, etc. Used it for over 10 years. One day I came out to find my battery dead. I charged it and it was fine for a few weeks, then dead again. I made a meager attempt at hooking up a meter and tracing the draw by pulling fuses one at a time, but found that hard to get any concrete evidence. On a hunch, I pulled the stereo and left it out for a few weeks. No drain. So I left it that way for close to a year (procrastination) and no issues. I finally bought a fancy flat screen stereo off Amazon and dropped it in. I figured maybe the really cheap one I got was not working correctly and causing the draw. With in a few weeks, dead battery. Sometimes it takes a week, sometimes it's fine for a month.

It appears to be something the stereo circuit/wiring and something that changed over time. I've inspected all the wires and the harness for the stock to stereo wires and don't see anything extraordinary. I'm out if ideas. Anyone have any thoughts on what it could be or how to troubleshoot further?

 

Is the stereo powering an amp? Does the stereo turn off when your turn the truck off?

 

No amp, stereo turns off, but like most stereos, there is a ignition power and an “always-on” power lead, for memory.

Of course, the always-on lead would be the key suspect for the issue, but like I mentioned, my previous stereo had both power leads and worked fine for years.

Maybe something change/broke in how that always-on power is regulated by the truck?

 

1998 Ranger 3.0L, stock radio

I had a similar situation for almost 2 years until yesterday. Same thing, sometimes my truck would sit for a week or two without a dead battery, other times the battery would be dead after a couple of days. I just never knew, so I eventually 'managed' the situation (most of the time) using a battery tenderer.

Anyway, a few days ago my battery finally died for good, and I replaced it with a new one. I figured it was a good time to hunt down my parasitic draw. Clamped my multimeter in line on the negative cable, monitored it, and discovered Fuse #29 (radio 'always-on' circuit on my model) was the source of my draw after my truck went to sleep. Beyond that not much made sense in that the time it took for my truck to go to sleep varied wildly from about an hour up to around 2 hours, but never the same amount of time. I also observed the amount of draw fluctuated, sometimes there wasn't a (parasitic) draw, and even if there wasn't, if I monitored long enough it would suddenly start drawing after a couple of hours or some other random amount of time...or not. The amount of draw whenever it was drawing was rarely below 120 mA, usually around 200 mA, but it would range/burst upwards of 500 mA.

Anyway, after a couple of days of trying various fixes I decided to just pull the fuse and do without a radio, and move on to a sporadic wiper issue I was dealing with. That's when I ran across a forum thread mentioning grounding errors. I looked at some diagrams, and discovered my wipers and radio share the same grounding point, so I sanded/buffed the left and right fender grounding points and connectors, and the same for the one on the front support by the battery.

No more parasitic draw!

Oddly enough, it was the grounding point near the battery that fixed my parasitic draw, not the left fender point mentioned in diagrams. Or maybe it was all three being cleaned that fixed it, I don't know, but it didn't go away until after I cleaned the last of the three near the battery. I also observed the 'time-until-sleep' became constant, and my truck would go to sleep at precisely 45 minutes with a 16 mA draw. I'm guessing I probably fixed my sporadic wiper issue too.

 

Thanks for the detail @fletcher969! Nice to know I'm not crazy. :)

I ended up doing a more brut-force solution. I wired the "always-on" radio lead to the cigarette lighter's positive lead. No more draw! When I have more time, I'll have to checkout the grounding points for a more permanent solution.