STUPID amateur electrical error

goblaneygo · #1 06-05-2016, 10:41 AM

My first post is going to be about how I am a rookie and spent most of my Saturday working on a problem that I caused to begin with. First I must state that I just bought my 2000 B4000 six weeks ago because I needed a 4x4 for ice fishing and sketchy boat landings. Had a B3000 that I bought new in 99' and drove for 17 years, I was sorry to see it go. Last weekend I was diagnosing trailer light issues and found a blown fuse number 7. Didn't have a spare so I swapped it with fuse 15 (Air Bag Indicator Light and Charging System Warning Light) thinking NOTHING of not having indicator lights until I could get a fuse. I didn't drive much last week and then the truck would not start on Friday. Did some troubleshooting and determined I needed a new alternator. Picked one up at Auto Zone (95A rebuilt Valucraft) and needless to say it didn't fix my issue. Replaced fuse 15 and of course everything is fine. 12.4V off, 14.6 volts running at the battery. Two quick questions about my stupid, stupid mistake: How the heck can this 7.5 amp fuse number 15 kill the connection between the battery and alternator? My second question is if I should leave the new alternator in place since the other one was the original from sixteen years ago? My alternator in my B3000 died in 2014 after fifteen years of use so I'm wondering if swapping out this one isn't a terrible idea. Looking forward to learning more about my truck and keeping it running for a long time to come. It only had 93K miles and the guy I bought it from had all the maintenance records and owned it since 3500 miles. Very happy to get my hands on it! Thanks for the help.....Mike

Mike In Bama · #2 06-05-2016, 03:51 PM

I'm gonna take a stab at this. You didn't state the value of both fuses and my 2005 is probably different.

If the replacement fuse was rated higher than the original, more current will go through the wire before the fuse blows. Copper is expensive. In all types of electrical and electronic fields you use the smallest wire that will do the job. (With a small safety factor, say 10%).

Smaller wire is cheaper and doesn't weigh as much.

Did the wire get damaged due to being overloaded? I don't know without more information.

Go ahead an leave the new alternator in. I just replaced a 21 year old alternator. It decided to let me down at night and on the interstate.

Rebuild the old one and you'll have a reliable spare.

goblaneygo · #3 06-07-2016, 11:49 AM

Mike - I replaced the 7.5 amp fuse with the correct rated fuse. I traded in the old alt to cover the core charge for the new one but thinking back I probably should have just kept it as a spare. Everything is working fine now and i learned a lot about the truck. Thanks for the help!