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Get thee a voltmeter Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 7 Jul 2005 05:45:12
In Reply to: Re: Eng will not crank after 25 min of driving, Allen, Wed, 6 Jul 2005 08:33:26 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The bit about headlights not working points to either the battery cables or the ignition switch. Get yourself a voltmeter.
With everything off, measure the voltage on the battery posts. Not the clamps, the posts. It'll probably be around 12.6 volts or so. Now, turn the key to ON and turn the headlights on. Measure the voltage at the battery POSTS. It should drop down to around 11 or so. If it drops way down, to like 6 or 7 volts, you've got a bad battery. Replace it. If the voltage on the battery doesn't drop, or doesn't drop much, measure the voltage between the positive battery post and the positive battery clamp. The voltage should be less than 50 mv (0.05 volts). If it's more than that, you need to remove the clamp and clean the post and the inside of the clamp. Some find sandpaper or Scotchbrite works great. Repeat for the negative post.
If that doesn't do it, again with the car ON and headlights ON to provide a load, measure voltage between the negative battery post and chassis. Again, it should be less than 0.05 volts. Any more, and suspect the negative battery cable, or where it connects to chassis. Repeat with the postive cable, from the battery post to where the cable attaches to the big lug on the back of the alternator.
A spark when attaching the battery line is normal, but isn't proof that the system can carry large amounts of current. That spark is maybe an amp or so, and lighting can run 15 times that. Starting is on the order of hundreds of amps.
If the battery and cables all check out, I'd suspect the igntion switch.
posted by 192.249....
, Wed, 6 Jul 2005 05:50:53, Thu, 7 Jul 2005 05:45:12 <-- Viewing This Message
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