2007 Mercury Mariner Alternator

RYAN4200669

MEMBER
2007 MERCURY MARINER

Electrical problem
2007 Mercury Mariner 6 cyl Four Wheel Drive Automatic

I'm trying to figure out if I need to change the alternator out on the mariner. The vehicle wont hold a charge when shut off for over about 4 hours. Just got the battery replaced about 2 weeks ago and it still needs to be jumped every time usually when I get off of work. I've been working on it today and after I found the location of the alternator I wanted to check to make sure it needed to be changed ( it's a pain to get to. ) So I looked online and ran the test of starting the vehicle and disconnecting the battery. It still ran fine I also turned on every electrical thing I could possibly think of Lights' radio ect. It still ran fine. Is ther any other tests I could perform or does any one know what else could be the problem?

1 Reply

WRENCHTECH

MECHANIC
20,761 POSTS

That doesn't sound like an alternator problem. It sounds like you have a parasitic draw from something not shutting off.

There is a procedure for finding a battery draw like that.

You will need a digital ammeter and a jumper wire with clips on the ends to do this.
First rig any door switches so you can have a door open without triggering the interior lights and unplug the hood light. Remove one battery cable and attach the meter in series between the battery cable and battery post. Take the jumper wire and also attach it the same way. Leave the jumper wire on for at least 10 minutes to expire all the automatic timers. Now remove the jumper wire and read the meter. Anything over 50ma is too much draw. The way you locate this is to start removing fuses one at a time until the meter drops to normal level. This will be the circuit with something staying on. Determine what components are part of that circuit and check them individually until the problem is isolated.