My V50 bat light comes on about 20 sec after starting. I metered the bat while running and the voltage jumps between 13.8 v to 14.4 and back, not running the bat reads 12.4v. I swapped bats and the same thing. The alt is less then a yr old. I'm thinking bad alt again. Ideas? thx.

 

Those voltages (running) are both within the normal(ish) range, with the 14.4 volts being a little high IMHO.

It might be interesting to scan the car with an OBD reader to see if it's giving you any more info - it doesn't sound like the traditional "battery not charging" issue, but perhaps one relative to "alternator output QUALITY (not "quantity").

 

The V50 has a weird pos bat connector that branches to 2 pos cables with what looks like a couple volt reg's on the 2 wires. I noticed they looked a bit crusty and removed and wire brushed them. So far so good, no bat light. Thx for the help.

 

Sounds likely - just a bad connection. That would explain the up-and-down voltages, especially when you're drawing a lot of power with the electrical system. Congrats!

 

Unfortunately it was premature, bat light came on again today. The puter is also now saying 'power system in need of service urgently'. This car always had electrical gremlins that would pop up out of no where such as the dash going crazy and the electric windows not working. Another thing thats been going on lately is the alarm system going off in the driveway when nothing is near the car.

 

Probably an offshoot of the same issue. You're losing power to multiple circuits, so look "back toward the battery".

The easy way to look for the problem - just wait until it's acting up, then use a voltmeter to check each point from the battery positive terminal down toward the fusebox(es). When you get battery voltage on one side of something, and significantly (more than a small fraction of a volt) less on the other side, you've found the source of your gremlin. Clean and/or replace that part and you're probably good to go.

 

Thx Habbyguy. I'm gonna concentrate on the fuse block on the passenger side under the dash. There was a water leak caused by volvo shorting the water drain from the sun roof to the firewall drain point. It would pour water into the car every time it rained. I gotta think it got that block wet a few times. I corrected that problem yrs ago and its strange that this materialized now. Again, thx.

 

Corrosion never really goes away - a wet fusebox is a bad, bad thing. The worst part might be that wiggling it around to troubleshoot it might "fix" it (very temporarily). You need to try to catch it in its failure mode and figure out which fuse(s) doesn't (don't) have the correct voltage.