Elec. Gremlin

We have owned this Mustang since 2008. It is a 2006 and has 27,000 miles. About twice a year it will drain the battery overnight. What makes it hard is when you put in a new battery or if your lucky and can save the old one, I may not have a problem for another 6 months. At one point I looked out into the garage to see a very dim glow. The backup lights were on but not brightly. I removed the lights and charged the battery but several months later it drained it again. It was under warranty at one point but the dealer could not find a problem. They said the next time it does it we will bring it in on a rollback. Problem is once you install a new battery it resets whatever is wrong and it has no issue for months. So again they can't find a problem. I'm on about battery 5 or 6 and the car can't be trusted. Car is clean, low miles, sits inside. Any good ideas. I don't care if it takes some parts or money to fix it as the car is not intended to be traded or gotten rid of. I just need to get it fixed. It appear it may be a long time to fix because no matter what I do it will be months before I'll ever know if it is fixed. Maybe all year and maybe tomorrow morning.

When the drain does happen what's the weather like? Is it rainy or very humid?

^^^ Good point. The reverse lights are commanded on via a reverse light switch on manual shift cars. This signal is applied to the PCM which then tranmits the state via canbus communication to the SJB (Smart Junction Box), which commands the reverse lights on and off according to the switch condition. The reverse lights voltage source is hot at all times. It woudl be interesting to see if the reverse light would actually engage the reverse lights with the key off. I don't recall that they light up with key off when i had a manual shift car, so it is not likely that the problem is in the reverse switch or on that side of the circuit.

Chances are this phenomenon was created at the SJB itself and IF it is the source of the power drain, the gentleperson from San Diego (lucky SOB untl he pays his mortgage and auto insurance every month LOL!) is on the right path. Moisture has been known to get into the SJB (located in passenger side kick panel) and reap havoc. You should inspect the SJB area and if presence of moisture is there begin resolving that as well as drying out the connectors and the SJB itself. Then see if the problem returns.

Other known issues are with the CD player unit as I recall. Been a few yaers (about 6 since I owned an 05-09).

With the low millage, I thak it you don't drive it much. A batt tender will help extend the batt life.

It's not the fact it isn't driven much. The car does shorter cruises as it's the the wife's car. Never winter driven so it doesn't see a lot of miles. It's never drained sitting for a period. It's always happened the day after being driven when it is dead. Has a float tender on all winter. Most likely to happen in late fall as the weather is getting a bit cooler. It is an automatic and those lights would be on with the car off and no key in place. Not brightly, just a dim glow. I'll try to get to the Juction box this week but the car is almost never in a rain or left outdoors. Still it could even be from washing it I suppose.

Remember that right hand kick panel is susceptible to water intrusion from the infamous clogged cowl drains. Now, I know your car isn't outside much but it may still be worth a look to see that the drain is clear. It doesn't take much crud to create a blockage - I know this from experience.

Our 2006 convertible had a battery drain issue which turned out to be the factory radio. Walked into the garage one morning to hear the CD changer cycling with nobody in the car. Seems a common problem. We replaced with after market and never had an issue. Wife also got stranded at mall once when only half of the electrical working. That was traced to a corroded ground lug under the hood on the front passenger side of the radiator support. Cleaned the mounting point and lug and put some electrical dielectric on it and have not had any issue.