sinkrun Posted June 26, 2009 Share Posted June 26, 2009 Was driving today allot around town and the battery light came on. Noticed the wipers were getting slow truck was running fine so I went to Advance auto. Battery was 4 yrs old they tested it and said the battery and alternator were both bad. Is this possible or were they trying to sell the battery also? I myself did not believe them so I asked them a couple of times are you sure. Well I did buy the battery light is still on and there tester says no charge at all. Is there anything else I should do before buying a new alt?? Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 27, 2009 Share Posted June 27, 2009 Check ALL your mains connections on the alternator, battery, starter, and body/frame grounds. Take them apart, clean the connectors up, apply some dielectric grease, and reconnect tightly. Inspect all the charging cables and wiring for burnt insulation and possible shorts. Then fully charge the battery, start her up and measure the voltage across the battery running at an RPM of 1500 or so. You should read at least 13.3 VDC. If not, the alt is probably shot. Link to comment Share on other sites More sharing options...
jpdocdave Posted June 27, 2009 Share Posted June 27, 2009 well when driving with a bad alternator, every battery will test bad untill returned to a charged state and then tested. but, it is very common, for a battery to go bad when an alternator does. sounds like your alternator is bad, and 4 yrs on a battery is good these days. Link to comment Share on other sites More sharing options...
fiatslug87 Posted June 27, 2009 Share Posted June 27, 2009 Start your MJ, pull one of the battery cables off the battery, if it dies you alternator is bad. Link to comment Share on other sites More sharing options...
Wildman Posted June 27, 2009 Share Posted June 27, 2009 I believe, its pull the Positive (+) cable off to check the alternator. Also, check your serpentine belt for looseness/slipping. Link to comment Share on other sites More sharing options...
fiatslug87 Posted June 27, 2009 Share Posted June 27, 2009 I believe, its pull the Positive (+) cable off to check the alternator. Thanks Wildman, I couldn't remember which one, it's been a while since I had charging issues, so I went with the vague answer, damn old age! :fs1: Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 27, 2009 Share Posted June 27, 2009 Since the OP didn't state what year his rig is, I didn't mention the part about pulling the battery cable while the engine is running. Never do this on the 91-92 OBDI HO's; it's an excellent way to fry the ECU. Link to comment Share on other sites More sharing options...
fiatslug87 Posted June 27, 2009 Share Posted June 27, 2009 Since the OP didn't state what year his rig is... Good point, all I have are RENIX. I wish everyone would put their MJ specs in their question or better yet in their signature (like us Hornbrod). :D Link to comment Share on other sites More sharing options...
jpdocdave Posted June 27, 2009 Share Posted June 27, 2009 yes, anything really from the 90's on its not a good idea to pull the cable while running, and don't even think about the vehicles now days. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 27, 2009 Share Posted June 27, 2009 Good point, all I have are RENIX. I wish everyone would put their MJ specs in their question or better yet in their signature (like us Hornbrod). :D :thumbsup: Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now