Car StartUp/Battery

OREO101

MEMBER
2005 FORD EXPEDITION
5.4L
V8
4WD
AUTOMATIC
200,000 MILES

Hi,

I had my bat, alternator and starter tested and they show as ok.
My battery is 1 year old, but it is Walmart's base cheap model.
Starter is about 1 year old also.
So I trickle charged batt and engine started up OK.
Then 1 hour later engine won't turn over.
All the dash lights go out.
Power win and power door will not work.
Should I replace or retest batt?
Or do I maybe have a parasitic drain on batt.
How do I test for parasitic drain?
I also notice that if I don't slam back gate I get a notice on dash that my lift gate is ajar.
Check cables?

2 Replies

CARADIODOC

MECHANIC
33,763 POSTS

By far the most common suspect is a loose or dirty cable connection at the under-hood fuse box, (Central Junction Box). The best way to verify this before assuming it's repaired is to measure the "voltage drop" across the connection. I added two arrows in the drawing to show where to put the meter probes. This only works when done while the problem is occurring.

For this to be a valid test, turn on the head lights so current is trying to flow. Set the voltmeter to the lowest range that can read up to 12 volts. Touch one probe to the stud on the fuse box, (black arrow), and the other probe on the terminal on the end of the wire that's bolted under that nut. The reading will be 0 volts if the connection is clean and tight. If you find any voltage other than close to 0 volts, that connection must be cleaned and tightened.

If you just tighten that nut, you may see a little harmless sparking, and the head lights will turn on. That's all a lot of people do, but shining up that terminal should be done too.

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