Hello,
99xc70 My wife called me yesterday, the car died on the way home from work.
As she was blocking traffic a nice policeman came by and noticed that the positive wire had come clean off of the battery. They put it back on and the car started and she drove home.
Today she called again, the car died. Dead battery. I went to check it out and the alternator seems like it is not charging. Had the car towed home, (thank you AAA) and i charged the Bat. started it up and at 2000RPM i am getting just over 12 Volts at the Battery. I know it should be around 14.5. The alternator is only a few yrs old. Did the Positive terminal coming off while the car was running cause damage to the alternator? Replacing that alternator was a pain, I dont want to do it again.

I did a temporary fix.
I ran a #2 wire from the Alternator across the bottom of the radiator to the battery positive term.
I covered the cable in a section of garden hose (oil proof) and just used the
threaded lug on the top of the old cable for attachment.
Now with fan on high and lights on high beam I am getting 13.7 Volts at idle on the battery. Seems good enough?

Get a battery terminal brush, and clean the cable and battery ends,
grease and tighten (10MM) Dirty connections invite problems.
Verify that the small wire (D+) to the alternator is tight.
You're getting low readings with your meter, you should see 12.6 on the battery.
about 14 with the engine running.

There's little to fail with the heavy battery cables, except the crimp on end fittings that you might get repaired cheap at a generator alternator shop should
they be bad. You can carefully eyeball the end fittings where the heavy copper wires insert into the crimp fittings, if you see green or nasty corrosion then
maybe there's a problem. But if the starter spins fast, I'd focus on the D+

Bill

Most recent tests.
Tester reads 13.9 at the alternator.
12.2 at the battery. this is with the fan on high and the headlights on.
The red cable at the Battery gets very hot at the clamp.
The cable seems pretty sealed I don't think I can clean it.
Is 13.9 en enough volts at the alternator with the fan and the lights on?
I seem to remember i used to get 14.5.

Does the neg terminal get hot too?
the current flow is the same, so if only one gets hot there's
an unwanted resistance there, either between the cable end and the battery,
or the wire and the crimp. Did you wire brush the battery and terminal ends?
I'd see a starter generator shop should you need to replace or repair the terminal end.

Where did you put the test leads when testing the battery?
Make sure they're on the battery and not on the cable ends.

13.9 sounds a bit low, but your meter may be off. see if another car battery reads 12.6
14.5 is way too high and lots of bulbs would be running too bright and burning out.

Neg term is not hot

I also suspect that the alternator may have been damaged. Though unlikely, it is possible.

What kind of alternator did you install a few years ago?
If it was a cheapie, it would not surprise me that it failed. "They don't make 'em like they used to."

I think it was Bosch.

The car died as soon as the terminal came off the car. Start the engine again and see if the red cable gets very hot to the touch. Many times there is so much corrosion at the end of the red wire that the resistance is too high to allow 14V to get to the battery. Check the voltage at the other end of the red wire also, right on the alternator.

You can replace just the voltage regulator, leaving the alternator in place. It is tight to get the rear plastic cover off (phillips screwdriver), but better than taking half of the car apart.
--
My back feels better when I sit in a Volvo seat

This morning I got 12.3 at the Battery, put the positive tester on the Alternator lug and got 13.9. When I went back and tested at the Battery, I was getting 13.9.
Strange. I think I might just replace the cable.

That proves there is resistance, causing the voltage drop and associated power loss in the form of heat. Let's say there is 30A charge current and 1.6V drop - that would be 48 watts. There is a bad connection within the cable - either between the conductors and terminal, or a break in conductors. I don't know the failure mechanism, but a logical guess would be conductors to battery terminal.

You need a new cable. Good troubleshooting.

I did a temporary fix.
I ran a #2 wire from the Alternator across the bottom of the radiator to the battery positive term.
I covered the cable in a section of garden hose (oil proof) and just used the
threaded lug on the top of the old cable for attachment.
Now with fan on high and lights on high beam I am getting 13.7 Volts at idle on the battery. Seems good enough?

Been trouble free for 11 days now

Nice 'fix' and the voltage at the battery sounds pretty good. You should find the last inch of original red wire at the battery has turned green and is useless for conducting electricity. There is a write up on Matthews or Volvospeed, with picks on how to repair it.

I always wondered what that threaded thing sticking up on the terminals is used for!

Did you zip tie the garden hose in one or two places?

--
My back feels better when I sit in a Volvo seat

13.9V at the alternator lug sounds OK for the alternator (the set point for those regulators is 14.1V, but temperature and load bring that down-- usually between 13.7-14.1V is OK). That's a pretty massive voltage drop between the alternator and the positive battery post-- as Klaus said, I'd expect the positive battery cable to be pretty hot to the touch. Cable failures are very common on these cars.

Be prepared for some sticker shock when you price that positive battery cable-- the genuine Volvo part was over $100 last I checked. Ipd has a much better price on an aftermarket cable (it isn't easy to replace generically because of the bolt on bit for the B+ cable)-- I think it was $39. The other tricky bit is getting the old cable out of the cable tray underneath the starter in the '99+ cars. I gave up and routed mine outside that tray.

Good luck!

Yes, where the cable connects to the clamp is getting very hot. To hot to touch without discomfort.

Time to replace it!

Good luck!

Just found this on an alternator site.

Warning: Never disconnect a battery cable while the engine is running. Doing so can cause high voltage spikes that can damage the alternator as well as other electronics.