Alternator Problem

matjprat · Post by **matjprat** » 15 Jan 2013, 20:01

Hi, All. I need some help with an alternator problem on my 1990 240 DL. With a multimeter, I get about 12.6v on the battery with the car off. Running, I get about 11.6v on the battery. Revving the engine does not effect the 11.6v. it remains pretty consistent. Presuming an alternator problem, I first checked the alt/battery lights on the dash with the key in position 2. The alt/battery light does not illuminate as it should as part of the exciter circuit. I removed the cluster and checked to ensure the light was not burnt out. It was not. To verify the exciter circuit was reaching the alternator, I pulled the red D+ wire from the alternator, clipped a jumper wire to it, and clipped the other end to the battery (-) terminal. I turned the ignition to position 2 and the alt/battery light (and other related lights) illuminated in the cluster. So it seems the circuit from the battery to the cluster and cluster to alternator is fine. I started the car and ran the jumper wire to the D(+) terminal on the alternator directly to to the B(+) terminal on the battery to see if this would "excite" the alternator. Nope, multimeter still indicates about 11.8v running measured at the battery. My question is, does this sound like an alternator with an internal short of some sort or possibly a ground (to chassis) problem. Thanks!

lummert · Post by **lummert** » 15 Jan 2013, 20:58

Is the belt slipping?

Post by **billofdurham** » 16 Jan 2013, 12:19

One quick thing to check is the earth (ground) wire that goes from the alternator to the engine block.

Also check the battery terminals are clean with good connections and no corrosion and that the cables are not breaking down in the clamps.

If they all check out OK then look at the regulator. There are two screws holding it into the alternator. The regulator can be taken off the alternator without removing the alternator. Remove the regulator and check the two brushes which look like black square spring loaded shafts. If they are worn out a good electrical shop can replace them or you can buy a new regulator for a lot less than a new alternator.

Bill.