Why is my battery drains and new alternator not kicking in???

Asked by Sep 14, 2015 at 02:28 AM about the Mercury Sable

Question type: General

It was dark outside and  I was flipping out batteries for a new one. It was only
for a split second but I hooked up the wrong color to the wrong posts cause I
had backwards. Well as a result I fried something , cause now after a tested
alternator and new battery it's still not right. There's no engagement of the
alternator and it's dead in about 20 mins then I gotta recharge the battery.
Fuses all checked and good, and all other usual suspect I believe. What's the
next step to fix the problem? Thanks

8 Answers


Get a technician's help, you are a danger to yourself and the vehicle. You could have damaged a fuselink or maxifuse. The heat created in circuits that were not fused the way you had it incorrectly connected ? the heat made can damage things you have yet to find by process of elimination. The wires in question feeding the alt. ? you need to find what you caused an open in, like the warning light circuit? does it prove out? charge fuse, what amp are you using, is it any good?

Best Answer Mark helpful

After those checks, using a test light, see where battery voltage is and is not. compare to electrical schematic for make, model, year, and accessories equipped. The wires involved in battery cables are not as well made as they appear, you could now have an open created where they should be connected and appear to be, but you may have burned them where they were merely crimped or stuffed during factory assembly of the part (cable end)


I should mention, most simple electrical problems can be corrected by cleaning the connections and providing proper ground. the neg post, the body, the engine should all be within .5 ohm resistance with a DVOM. if you do not have one call a friend who may know more and has one. You would be surprised at the diagnostic repair cost. even if they fixed nothing. be more careful, read a service manual, have a helper watch out for you or hire it done. Your automotive computer is at risk as well as any SRS you may have.

As far as I know battery and alt. are working fine. Failed to mention when mixing up cables the horn sounded very loud for that split second. Battery light on and battery is at normal numbers. It's as if the Alt.is not working from the main computer. Could it be a EEC or MAP computer? I'm not the car guy but asking because my mechanic is stumped and says car is not worth it. But I'm not in position to buy now


The alternator requires only the plug and its wires be good, the output wire connected, and be grounded by its case. there is no computer decisions there but its regulator has electronics within including the ability to activate it and respond to its range of operation...............The fact that the battery light is lit should be telling you, there is no current shutting it off. either the alternator does not charge, the battery is below spec for voltage, or there is damage in that circuit.


It can also mean the warning light circuit is not correct now, a fuse you missed, a connection damaged, or not the right readings would be found at the plug on the alternator. look also at the starter relay, the B+ cable goes there. The other large lug is the cable to the starter? I am asking how yours is wired.........anyways, the fuselinks for mains go to the B+ cable side and are "hot at all times" in most ford schematics. by design. did one get stretchy ?


as long as that light is on you can expect a dead and dying system. self discharging the battery to run the car and its systems.


Your car is not worth it ? that's your "mechanic's" answer ? Find out what year the POS is and look up a schematic for charging or starting and charging through autozone. my friend ned digger could fix that problem.

Your Answer


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