My 91 240 has about 300k miles on it. Recently, the alternator has been slacking. I had it tested and it was pretty much shot. I decided to replace the battery and the alternator. When I replaced the alternator, everything seemed fine until I turned the car off. When the ignition is "OFF", the battery light comes on. Even when I REMOVE the key from the ignition, the light stays on. The battery light goes out when the car is running. The new alternator seems to be working correctly, but of course the battery is being drained when the car is not being used. Any suggestions?

 

I would say the ignition switch is bad or a wire is being shorted to 12V. Is it only the battery light on with the key out?

 

I have a 1986 240DL and im having the exact same problem.My alternator is brand new and my battery is new. And all my wires are reading only 12.4v when running.(red cable coming off battery and red cable coming off alternator)
My battery light wont go away even if the car is off and the key out.I dont know if im going to need a new ignition switch or new wires going to it, plus all the wires look good.
Please help!?!?!?!?

 

Try to wiggle the key in the ignition switch. Also remove fuse 13 and see if the light goes out.

 

I already tried to replace the fuse#13 and wiggle the ignition.Also the ignition switch wont start the car but it will turn the other stuff like the fuel pump relay,radio, etc...
I hard wired an extra switch in the dash to start the car that ran straight to the starter.So the contacts on the inside of the ignition switch wont start the car but will do everything else, except maybe the contacts went out on the alternator part of it.I dont know but if i can find a way to fix it, that would be great because thats the only thing wrong with this car.It has 300k miles on it. So replacing the whole switch is like a 15 step job just getting it out.WAY to much work, the switch is $75 used and i cant afford a mechanic to do this.I need help?!?!?

 

With the key on, car not running, measure the voltage on the small and large red wires connected to the back of the alternator.

 

12.5 with ignition key on, 12.1 running

 

make sure the ground wire that connects the bottom of the alt. to the block is in good shape. With the car running you should see no more than ~.1VDC while measuring the case of the alternator with one meter probe and the fender of the car with the other.

You should have only around 2VDC on the small red wire with the car not running since its grounded by one of the brushes of the regulator.

 

everything checks out and my ground is good on the alternator.The little red wire with spade terminal off the back of it reads 5.1v while running and 1.5 not running

 

Is this how its hooked up? Most times nothing is connected to the "spade" terminal.

 

why is that?The old alternator on there was hooked up.Is there a difference?

 

For the alternator shown, that spade is for an external capacitor.

 

the spade on the alternator or coming out of the sheath with the rest of the wires?Plus isnt the battery supposed to read 14.0v when running, if the alt. is working.Also the alt. i have now came with an adapter that covered the terminal that was black and said 2.2v on it.

 

Here is a pic of one I replaced on a 240 today.Pic is from my phone(low quality).


Dan

 

so the black piece covering the terminal need to be on there?

 

If you are referring to the pic I posted,the little black box connected to the spade terminal is for radio suppression.88 to 93 the radio suppression relay is mounted at the overflow reservoir.


Dan

 

i need to know what i can do with the extra small wire coming out of the sheath going to the alternator.The hot wire and the ground wire are hooked up.The alternator i have has the the radio suppressor on it already, so...Also what is the battery voltage supposed to read when the car is running?This is all i need to know and i really thank everybody for the help.

 

Maybe post a picture of the wire you are refering to. Measured at the battery, idle, no head lights - I get 13.9 VDC.

 

well there's a small wire(RED) that comes from the ignition switch, through the fuse box (#13),to the battery charge failure lamp, and then to the alternator.And i think it goes to the small square terminal on the alt just like the original bosch alt.That exact wire comes out of the sheath along with the large hot wire going to the alt. and a small black wire going to the engine block(sensor).The alt. i have now has a radio suppressor covering that small square terminal? So the small wire(RED) has to go somewhere for that lamp to light.So what can i do?What do i do with the radio suppressor?

 

my new alt. looks just like the alt. Dan posted (thread#14), but it doesnt have that little square terminal on the ground post of the alt.?hmm...but other than that its the exact same thing.Well?