Headlights and dashboard lights went haywire and then just SHUT OFF while driving at night. Van still drove though. What could be the problem?

Asked by JCRIOS Nov 23, 2014 at 01:17 PM about the 2004 Pontiac Montana

Question type: General

I am pulling the battery to take it in to have it tested.  Bad alternator possibly?? how can I
test the alternator without pulling it?  I am no mechanical genius by far, but have fixed
small stuff myself on my vehicles such as alternator, brakes/rotors, etc.  The van is at
about 140,000 mi and have already had †he wheel sensor fixed and head gasket done.  
Should i just take it to my mechanic and have them do a diagnostic on it?  PLEASE save
me money.  Thanks.

3 Answers
30,130

mikeatpriestlake answered 9 years ago

battery has to be fully charged to perform a load test. also, to test the alternator output, start the car, set your multimeter to volts d/c. put the red test lead on the pos post on the battery and the black on the negative. turn on the headlights,and wipers, just a few accessories. the alternator should give a fairly steady 13- 14.5 volts all the time. if not, it is bad.

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JCRIOS answered 9 years ago

Mike took battery in to have it charged because thought my charger was not working properly. They could not get a full charge either meaning it was bad. Put new battery in and did what you said. Yep, obviously need alternator as well. Figures. Also did a double check and unhooked negative terminal while van was running...engine immediately shut down. Thanks for saving me cash on a diagnostic test.

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