car died, think alternator, please help.

More threads by irvine


New Member
Maroubra, Sydney
hey everyone I need help and sadly this is my first post,
ive just had my first breakdown and I'm stumped as to why its happened....

so today I left the side lights on for a couple of hours by accident, the car didn't start as usual and struggled like it would from a low battery which was to be expected. so I waited a good 5 mins letting it idle then dropped my girlfriend off a good 15 drive away, on the trip the battery light stayed on and when stopped at traffic lights using the indicators it felt like it was going to stall. but after about 20 mins of driving the light went out and it felt good again.

once home I turned the car off and tried it again to see, and it didn't start.... it did bring on the dash lights and prim the fuel pump but couldn't turn the motor over. so got a jump start and it fired up instantly.

i tested the battery and it was 11v, let it run for a wile and tested it running to check the charge and it was dropping now to 10v. obviously that points to a stuffed alternator.

am i right?

other question is what alternator would i need? the cars a 1974 280SE.

huge thanks for any info.


and 111/126
Hi Neil,

Welcome to the forum.

Could be the alternator, or could be your battery has a dead cell and is not able to hold a good charge.

Either way a voltage meter could help here to see what sort of output you're getting from the alternator when the car is running and if you rev it up a bit what it changes to. If you're seeing low voltage when running then it might just be the voltage regulator on the back of the alternator which is quite easy to change.

If you have a dead cell, you'll probably see decent voltage when running but it will go back low again as soon as you turn off the car. You can take the battery to a battery shop or somewhere like supercheap and they will test it for you as well.

I had a battery with a dead cell and it behaved somewhat like what you're describing. Battery didn't have the juice to start the car, but was ok to keep it running once going. Luckily this car is a manual so was able to roll start it if it stalled. Old british car so the lucas starter was good at exposing weak batteries.



Sydney - Centre of Civilisation
I agree with Bryce - you do need to diagnose the problem which could be a faulty battery through to a voltage regulator or the alternator. It could even be the power lead is faulty. My recommendation would be to have it all tested by someone reliable such as
In general they are spot on with their diagnosis.


New Member
Maroubra, Sydney
ok so update from todays tinkering...

I pulled the battery and all relative hardware, I could not believe the amount of dirt grim and caked in oil on the wiring connections and earth strap from the alternator. ive cleaned EVERYTHING and sanded all nuts, bolts, screws, lugs and connections.
the regulator was a mess, caked in grime and as everyone suggested was worn substantially. ive put everything back check all connections, even refitted the regulator and what do you know, it fired up no problem. I tested the voltage of the batter before I connected, it read 12.3v and connected with the engine on load it was reading 13.8v.

some pics below to show the state of the connections and regulator:

terminal block under battery tray:
W116 by Neil Irvine, on Flickr

connections inside alternator:
W116 by Neil Irvine, on Flickr

alternator cables/connector:
W116 by Neil Irvine, on Flickr

and the regulator in question:
W116 by Neil Irvine, on Flickr

i really want to change the regulator asap as from the pics its stuffed, i dont trust how long its got left. problem is the suppliers near me only stock bosch regulators and they need the part number.

can some one please give the part number i need??? its for a '74 280se...

thanks for all the info guys,


Give the engine etc a good steam clean with a hot pressure washer (you can hire them from a couple of places) and degreaser, but be very careful to avoid the delicate parts.
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