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Alternator problems?

Started by oscar, 16 June 2005, 07:44 AM


Hi there,

Need help with my alternator. My 1973 350se M116 engine whilst idling, the multimeter shows almost 13 volts sometimes over, never up towards 14.  With lights on just above 12V.  Turn the fan on and it starts dropping below 12V. Any decent long trip at night 200km will see the motor die.

I pulled the alternator apart, brushes are about an inch long.  All terminals have been cleaned and all the windings seem to be intact, insulated and ends soldered to respective connections.

Could it be the battery,it's only 18 months old?  Is it voltage regulator? Got no idea where that is.  

As a sideline two more things which may or may not be relevant.  

Firstly, the radio was humming with the revs.  It got pulled out as it's a restoration project on its own.  However does that symptom indicate that the supressor is shot and if so is that the brown rectangular thing attached to the back of the alternator?

Secondly, the alternator is a reco exchange unit and has been sprayed with silver paint that also covers the usually brown ring that separates both halves of the alternator.

Any help would be greatly appreciated. Cheers.
1973 350SE, my first & fave


Thanks yet again Styria, I hadn't thought about the aerial which is placed in front of driver unlike most 116's I've seen that have antenna behind left rear passenger.  My antenna seems to have a firm grip on the panel and is manualyy operated but I will look into it.

I think I've learnt something about ignition leads.  Is it true that there's not one suppressor for the electrics but one suppressor on each lead, them being the long metal part that attaches to spark plugs?

I'll get back to you on the alternator and other stuff, work calls. Huru
1973 350SE, my first & fave


The voltage regulator should be bolted to the back of the alternator; held down by two small cheese-head bolts.  If you remove it, it will have two brushes on it.

Sounds to me like your alternator is barely charging.  Is the dash light coming on at all?  If you just turn the key w/o bumping the starter, the dash light should kick in.  If not, then get that fixed. That light is a necessary part of the circuit.

With the unit apart, I guess it would be a bit hard to tell if the light glows weakly.  Have you checked the diodes for proper function?



Thanks cth, found the cheesehead bolts and know where it is now, just can't remember what that area looked like when I pulled the alternator apart. I know I didn't undo those bolts though.  Next lot of days off I'll take the alternator out again and have a closer look.

Also, are the diodes the three round discs visible from the firewall side of the unit, each with one wire soldered on respective lugs on the internal side of the alternator?  Are they simple to test or is it time to see an auto electrician?

FYI I reckon the dash warning light's ok.  It lights up bright before engine's kicked over and the more the battery discharges, the brighter the warning light gets.

PS, Styria, re:suppressors
Mmm, well the plot thickens.  I need more than suppressors.  I have mixed leads, 3 types all up, 4 silicone without suppressors thanks to an incident involving master cylinder and brake fluid.  But that's for another thread, I have more question's.
1973 350SE, my first & fave