Alternator not working - shouldn't battery light come on? - Page 2 - PeachParts Mercedes-Benz Forum

chetwesley · #16 05-02-2012, 12:13 PM

Quote:

Originally Posted by gastropodus

Yes, you do have to pull the cluster to get at the bulb (not that big a deal in W123). However, the real issue which I don't think that you've answered is, does the light come on when you rotate the key to the first position before engaging the starter? That's when all of your warning lights are tested.

Kurt

Sorry, I forgot to mention it - we are talking about the position where you glow the plugs, right?

The light does not come on.

chetwesley · #17 05-02-2012, 12:47 PM

I pulled the bulb - and by the way you do not need to remove the cluster, just the panel below the driver's dash and you can reach up there.

This is an incredibly dumb question but I will go ahead -

The bulb is not visibly burned out, should I just run 12v DC across it and see if it lights up?

Also, what other parts of the charging system would cause the bulb not to go on in the 1st position? Would the voltage regulator being bad also cause this?

rrgrassi · #18 05-02-2012, 12:56 PM

You can do that. Even a 9v battery will light it up, if the filament is still good.

chetwesley · #19 05-02-2012, 02:35 PM

The bulb was fine.

I replaced the regulator and the light comes back on.

One of the brushes on the regulator had worn all the way down. When I took out the regulator one side was just a spring and a wire (no brush). The dude at the alternator shop said that meant my rotor in my alternator was untrue causing the brush to wear extremely quickly. The regulator was new a few months ago.

Also it is worth noting that the brake wear light is on that circuit and was not lighting up until the voltage regulator was replaced.

Murkybenz · #20 05-02-2012, 03:50 PM

Quote:

Originally Posted by chetwesley

The bulb was fine.

I replaced the regulator and the light comes back on.

One of the brushes on the regulator had worn all the way down. When I took out the regulator one side was just a spring and a wire (no brush). The dude at the alternator shop said that meant my rotor in my alternator was untrue causing the brush to wear extremely quickly. The regulator was new a few months ago.

Also it is worth noting that the brake wear light is on that circuit and was not lighting up until the voltage regulator was replaced.

I have had similar over here in the UK on a 89 300d om603 non turbo,basically as yours one brush worn away and bad contact.

Jogging the engine over on the key would see it make contact and work (glow light etc) ,I had just the main battery light and ABS but no other lights and the blame was given to the ignition barrel switch at first but that checked out ok and of course when I cranked the engine when playing around with the switch then it all came back and worked.

rrgrassi · #21 05-02-2012, 08:57 PM

Was the stator still in good condition and not gouged by the spring or wire? Any roughness will eat up a new brush. I learned the hard way on an old Pontiac I owned. I had to disassemble the alternator to get to them.