Hi,

My 940 will not hold a charge. I replaced the battery, removed the alternator and had it tested three times the test came back good. If i put the car on a charger it will run for a few days as long as I switch the automatic lights off. I tightened the alternator belt and cleaned all of the connections. I cannot figure out what is wrong with the car. I'd appreciate any help.

 

If the battery is OK, then you have a short somewhere which drains the battery.
Disconnect the negative cable and measure the current draw between the negative cable and negative post, using an ammeter that has a 10 amp range. If there is a noticeable draw, then pull one fuse at a time until the draw goes away. Now you know what circuit is causing it. Look in the owner's manual, to find which fuse number it is and what functions are on it. Look at those devices one at a time until you find the exact cause.

 

I preformed the test. I had an 11 volt draw from the terminal to the post. No matter which fuse I pulled the draw was still there. Confused

 

wait. current is measured in AMPS not VOLTS.

have you verified that your alternator is charging your battery when the engine is running? with the car running, the battery voltage should be 13.6 to 14.2 volts.

alternators can test fine out of the car, and still not be working right for a bunch of reasons... lack of D+ kickstart voltage (supplied by the BATT/ALT light in the dashboard!), lack of adequate grounds.

 

It's only at 12 volts with the car running and the battery fully charged. Also at the back of the alternator it's only spitting out 12 volts too. Not sure if that could be the battery light on the dash.... Or if the alternator is possibly bad even after the bench test.

 

ok, so... your alternator is NOT charging the battery.

first, the alternator needs a 'trickle current' from the alternator/battery light in the dashboard. this light is connected to the ignition switch, and is on in 'II/Run', and the other side of this light goes directly to the alternator D+ terminal. test1) light should come on when you turn on the ignition, and go out after the engine is started. thats normal operation. test 2) when you turn the ignition on, you should read close to 12V at the D+ terminal on the back of the alternator. this is the smaller terminal, NOT the big red wire.

secondly, the alternator needs a good ground. start the car, confirm you're only seeing 12V across the battery. now, put the black volt meter lead on the battery - terminal, and put the red volt meter lead on the alternator body, or its ground screw. you should see very close to 0 volts. if you see 13.6V or whatever, then the ground isn't complete. now measure from battery - to fuel rail ground screws (scrap them off to be shiny metal. also should be zero. measure from fuel rail grounds to alternator body. also should be zero.

 

The only lights that come on in the II position are the seatbelt and srs lights. At the smaller plastic connection at the back of the alternator I wasn't getting any voltage at all. On the larger red wire I had 12 on the smaller positive nothing.

 

Although when the car won't start all of the lights come on. I.e the battery is so drained it won't turn the car over

 

when you turn on the ignition, ALL the lights on the dash should come on, then go out when things start.

there's a fuse on the back of the instrument panel in the indicator light circuit... if its blown, none of them work. per my diagrams, its above/behind the right turn signal blinker light. the power goes into the instrument panel on the 4-pin inline speedometer connector, on pin 4, this is a blue-red wire directly from the ignition switch pin 15R. If that fuse is blown, tho, none of your instruments would work right, its power for everything except the clock.

the alternator light is wired to connector C pin 16, via a red wire to the alternator D+ (small terminal). Connector C is the large slanted inline connector on the clock side.

 

wait, what? so if the battery is charged, most lights don't come on when you turn the key on without starting the car, but if the battery is mostly dead, they DO come on???!

thats *TOO* weird for me.

 

Your alternator should put out 14ish volts. 14.2 is a common healthy number. I'd say you have a diode issue, friend.