I've searched the forums and found a few helpful bits, but nothing specific. I replaced my alternator today, but was unable to reconnect the neg battery cable due to sparking. I didn't mess with anything apart from taking the cooling stuff off to get access to the alt, removing the belt, and the 2 bolts holding the alt in, as well as the + lead on the alt post and the clip-in wire on the bottom. Why would it suddenly decide to spark when reconnecting the wires with the new unit? Was there a second wire to attach to the post on the alt other than the red lead that I might have missed while reaching around etc? I'm fairly new to car work, with zero understanding of the electrical system. My experience is limited to brake pads, basic stuff, I did a fuel pump a while back. This is a 2000 S-10 pickup. Any help would be appreciated. I couldn't find any obvious shorts anywhere, and the wires looked ok. When I started putting the battery cables in, the battery began to smoke, and I quickly disconnected everything. Hopefully I didn't kill the battery, since it is only 3 months old.

 

Remove the red wire from the rear of the alternator, make sure it does not touch ground.
Connect the negative battery cable to the battery, there should be a slight spark to "wake up" memories in the onboard computers, (NOT a violent spark with a "snap" sound). Now, with a quick motion, touch & release the red wire to the post on the rear of the alternator. There should be no spark at all. If there is a spark, the alternator is bad.

 

Thanks I'll give that a shot in the morning and report back.

 

I did as you said and had no problem. So I reattached the alternator and lo and behold, no problem reconnecting the battery, and I started the truck with no problems or explosions. I think I found the cause of the problem to be the red lead coming off of the back of the alternator had a small crack in the rubber boot, and I had put the wire on first because I can't reach behind the alternator at all. Thus, when I had bolted on the alternator, the red wire had twisted itself because it was facing the engine and doing a 180 degree turn, so it must have exposed itself to the engine block. When I put it on again this morning, I made sure to keep the red wire so that it would face out in to the empty space and was able to hook everything up with no problems.

 

Thanks for posting back with the "fix".

 

Well. Turns out all is not well. Although it was running fine, it wasn't charging the battery. So, I took the brand new alternator that i just put in back out again, and had it tested and it failed in the 'charge volts' category. So, new alternator arriving tomorrow. Hopefully it goes in without a hitch.

 

Put in the new alternator, but still not charging the battery. I guess next I'll check my grounds and test the wire from the battery to the alt post. Time to take it all apart again!

 

The red 10 guage wire on the back of the alternator should show battery voltage at all times. Starting in 1999, the VCM controls the alternator. If you have a 4.3L engine: At the VCM connector #C3, pin #5, is a red 14 guage wire that goes to the "L" terminal on the alternator. If you have a 2.2L (S or T-10 pick up): The red wire is at connector #C1 pin #74. Voltage should be zero with the ignition off, and will vary when the engine is running.

 

Tested the resistance of the alt lead to battery and was OL. So I unhooked that from the back of the alt, and followed it around removing all the shielding etc on the way, to where it connects to a little fuse relay behind the passenger headlamp (under the battery compartment) and the fuse link was blown. The other lead at the terminal there checked out ok to the battery, and the + and - terminals on either side of the fuse indicate that the fuse is ok, so I am off to buy some 10 ga wire, a fuse link and a connector thing, some shrink tubing and electrical tape to put the hose cover thing back on. And then crossing my fingers again.

 

Found an exact match for the fuse link at the junkyard, came home spliced it all in and it's charging the battery now. Yay! However, for some reason, my fuel gauge is now not working the needle is sticking all the way to the right, at about the 5 o'clock position. Any thoughts?