Hello all, I have an 85 300d. My battery started dying on me and I replaced the alternator twice now. I am noticing the battery light, brake pad indicator and brake light no longer turn on when I switch the key to the on position. I believe this is preventing the alternator from energizing due to the posts I read explaining the importance of the blue wire coming from the alternator that is connected to the 3w dash bulb for battery. My bulb is good. My dummy lights only come on very sporadically and when they work my alternator charges the battery. Any way to bypass this or is there a work around ? Any helpb would greatly be appreciated. Thanksgiving is tomorrow and at this moment my road trip is definitely off. :-(

......forgot to mention my glow plug light and all my guages and dash lights are functioning with key

Contact for blue wire at alternator may be bad. Take the connector off the alternator (undo wire clip lock first) and look at the contacts for corrosion and looseness. Clean and lightly crimp to restore contact.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I have the checked blue wire for for continuity between the alternator plug and the round connector by the coolant overflow. I am getting voltage to the blue wire with the key on. However my battery,brake indicator, and brake light do not light up with the key on. Looking at the wiring diagram for the charging system it appears that a blue and red wire on terminal number 6 of the instrument cluster plug supplies power to the indicator lights, I have checked this terminal with the key on and am getting voltage however the lights do not receive the power for some reason. Is this indicative of the instrument cluster having a fault ?

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You should not have 12 volts on the blue wire until the engine is running. In the bulb check position you should have closer to zero (probably around 2 volts) for the lamps to light.

With the key in the bulb test position, short the blue wire to ground at the alternator & see if the bulb lights. If it does then you have an alternator problem. Could be as simple as a bad connection between the regulator and alternator case. Also the original regulator had a 68 ohm resistor mounted to the regulator. Is it present on your's?

What is the history of the alternator replacement? Were they used or remanufactured? By what company?

From all of the recent reports of ignition switch problems, I'm wondering if that might be the problem.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Per the diagram you posted, the blue excitation wire for the alt is not fused and is powered by the same contact on the ignition switch, which also powers fuse 12 (fuse 12 powers the brake warning as well as other items such as turn signal, tach, pwr window relay and a few other devices). Judging from your description, an intermittent ignition switch is the problem. Try turning the key off/on a few times and see if you can get the indicator lights in the cluster to come on.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thank you for the replies, the alternator is a car-quest reman. I am getting 12v to the blue wire with the key on regardless of whether the engine is running or not. I took the blue wire and shorted it to ground and all three of my warning lights came on. As for the resistor I dont see it, but then again this is not a stock alternator. Should I return this alternator again or ? ? ? ?

funola....... the dash lights come on sporadically and intermittently with multiple (MULTIPLE) key cycles.......... SOMETIMES

Here's a few easy things to try:

1. With key on, have someone jiggle the alternator connector while you watch the battery light in the instr cluster. If the battery light goes on and off with the jiggling, you have a bad connection at the alternator.

2. With key on, and the brake warning lamp is off (it should be on), check if the power window and brake lights work when you step on the brakes. If they don't work, fuse 12 is blown.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

It sounds like the ignition switch is your problem.

Fuse 12 also powers the blue wire via the brake wear indicator lamp, the resistor and diode as in the diagram. Remove fuse 12 and check for 12 V on the blue wire again and report back.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Where are you checking for voltage of the blue wire? The only sure place is at the alternator connector, no where else.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I have checked for continuity on the blue wire from the alternator. Its good
Fuse 12 is not blown, my temp and fuel guage register. Windows operate.
Per the diagram it looks like terminal 15 on the ignition switch corresponds to terminal 6 on the instrument cluster plug. With the key on I am getting voltage to terminal 6 on the instrument cluster. I can assume that the ignition switch is working ?

If your ignition switch was at fault, your light would not come on when you ground the D+ terminal (blue wire) at the alternator. The resistor can only be seen with the regulator removed. I have never tried a regulator without the resistor so I don't know what the symptoms are without it, but it is in the lamp circuit to ground. If you remove the blue wire and then take an ohm reading to ground from the D+ terminal you should get the resistance reading.

My personal opinion of rebuilt alternators is that they are mostly rubbish unless rebuilt by Bosch.

I agree that it is likely the ignition switch. But, you could remove the Alternator and have them test it for free and elimnate it as a cause of the problem.

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84 300D, 82 Volvo 244Gl Diesel

If you need to drive the car and don't want to get stuck with a dead battery, this is what I'd do:

Take any light bulb bigger than 3W, connect one side to battery + terminal, connect other side to the blue wire terminal of alternator connector (use an alligator clip). Start the car and rev engine above 1500 rpm while checking charge voltage at battery, anything above 13 V to 14 V is good to go. When you get to your destination, unclip one of the connections of the bulb so it does not put a drain on the battery.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked