I have an old beater 1990 240 with about 375000 miles on it. It has developed a charging problem. On start up, the battery light stays on, and there is only 11-12v at the battery while running. But, rev it just off idle, and the battery then starts charging at approx 13.90 volts.

But now, this too has become inconsistent. I pulled this alternator off another 240 that was charging, and soldered new brushes into the regulator. The thing is, it did the same thing (batt light on until revved) with the original alternator on it. So now I am starting to wonder about the fat red wire that goes to the alternator. It is pretty corroded at the alternator, and quite a few strands of the inner copper wires that make up the cable are kind of fraying at the ring connector. I am going to crimp on a new ring connector and see if I see any changes in my voltage readings. I had to crimp on a new ring on the red cable that goes from battery to GM fuse on inner drivers fender

I also had a bad battery, which I have since remedied. That was also making diagnosos a little tougher. But now days, I suspect the battery in about 7 out of 10 electrical problems in these old cars, and with the crappy quality of batteries anymore.

Any help is appreciated.

When this first started, the batt. light would come on, and stay on until revved
off idle, then it would charge at 14v. Now, the batt. light comes on,
(sometimes, not every time) but charge voltage only reaches 12.5v. I have read
this could be a symptom of a problem with the exciter wire, and have done a lot
of reading on it. I have 0 ohms at the gray connector at firewall from the back of the
alternator on the red exciter wire. The battery light lights, so wouldn't that
indicate the wire is good to inst. cluster?

I have a good battery in the car, and autozone tested the alt. and says it is
good, but I am having my doubts. I have ohmed out all of the other wires from
various post that I have read, and checked all grounds. Used dielectric grease
on all connections, including the 25 amp fuse on fender well, which also ohmed
out good everywhere. I pulled all spades off the batt. dist. block, and assured a good connection and used dielectric grease on them.

I found
this old thread about a similar problem...http://www.brickboard.com/RWD/volvo/13
85648/220/240/260/280/link_good_wiring_diagram_observation.html,
and was wondering, if this schematic is saying that all bulbs must be in and
working for the exciter circuit to be complete? The PO removed some bulbs in cluster, one for sure being the SRS bulb I have ohmed the alt. wires to
the batt, checked chassis, and block grounds for the alt.Any suggestions would
be appreciated.

If the big (B+) wire is showing deterioration at the connector, by all means replace the connector and crimp to nice freshly-exposed wires. I recently had one break off with just the slightest touch of my finger. But the fact the system fails to charge until you cross an RPM threshold indicates a fault in the exciter circuit. Inspect the small red wire (D+) on the back of the alternator, and again where it passes thru the grey plug connection on the firewall behind the intake.

I recently had charging woes on a 1988 245 that turned out to be from a poor electrical connection where the L-shaped three-wire plug attaches to the back of the cluster.

john
--
1989 245 233K / 1993 945 127K

Dino,
Thank you for the response!! I will change out my questionable ring connector at back of alternator, check grounds where they should be and none where they shouldn't be, and follow the path of the exciter wire. I think I could have multiple problems.

Two different alternators, and having a known battery in it, makes me think it is something in the wiring. Unless, I have two identicle alternators with the same problem, which is unlikely, but possible.