Alternator, Voltage Regulator, or Other?
 

I was driving my newly acquired '85 300DT and everything was peachy, then seemingly suddenly I started losing electricity. And fast. Within five minutes (at night) I was out of headlights.

I just bought the car a few days ago. The previous owner apologized because it was a remanufactured Autozone alternator, albeit a new one.

I had alternator tested at Autozone while still in the car. With the car off and his tester on the (dead) battery terminals it got a reading of 12 or so volts, but when we started the car the reading dropped to 3.4 volts. He said this indicated that alternator was not bad. Admittedly, I don't quite understand how that test works, so I'm not sure if the Autozone tech's analysis was correct.

Symptoms/Tests thus far:
--Dash battery light stays on
--Battery takes a charge, car starts fine until battery drops
--Multimeter on battery (12V off, no increase while running, steady decrease w/ headlights on)
--Multimeter from negative terminal to block w/ cable disconnected (12V)
--Connections in grounding block all fine
--Cable connections on starter good.

So I'm not sure where to go from here. Thanks for any input you might have!

Chip

There must be a reason why the dash battery light stays on - have you checked to make sure whether the alternator has been correctly connected?

Indeed. All of the connections are solid.

Good Morning Chip, and Welcome to the Forum.

Finish filling out your signature as to the model of your car, and the area you live. might a forum member close to you. Safety in numbers :rolleyes:.

85 sedan 4 door is a 300D, common knowledge it is a turbo. or a 85 300 Wagon is a 300TD, w/o the added "T".

Do a search, there is a wealth of Info compiled on just about every subject. The resourced Tab at the top has DIY links and articles by model and engine.

The Bosch Alternator is the prefered one to use, not sure what Autozone kragan etc... sell.
The Bosch has a replaceable Voltage reg on the back of the Alt for around $30.

The buy parts tab above in the on-line catalog, this helps to support the forum. Phill that runs it can get you just about anything except a new rust free factory body.

there is a thread running now on this same page with Alt charging problems, might be of some help.

www.peachparts.com/shopforum/showthread.php?t=264973

I was having a problem a couple weeks ago, and it was the ground cable from the block to the body. was clean and tight, but the paint (because of the new engine) didn`t give me a good ground. so sanded the paint off the area on the bell housing seemed to fix it.
My first indication of a probem was the temp gauge jumping around, and suddenly pegging all the way to the top :eek:. thought it was something else like a ground at the back of the cluster.

The thing that confused me, when I removed the key, and engine off, the battery light stayed on.

There is a black plastic box on the R/F fender near the battery. open the cover, there are 3 screws connecting some wires.
the 2 wires coming from the alt connect to this block. then down the the starter, battery and think to the starter switch and battery light.
Make sure these are clean and tight.

Also, 2 of the screws can be jumped here to start the engine. Had Neutral safety Switch (NSS) fail one time and this got me started.

Charlie