I transplanted an OM617 in a 4Runner, and I have an issue with the alternator. The engine is from a 1983 300TD. It sounds like Mercedes uses some type of diode with the "Not Charging" idiot light. Apparently, it won't charge if this light is blown. I have no dash parts to trace how they did this.

The alternator has three wires coming out. Two go to the positive side of the battery, the third goes to somewhere in the dash and involves the idiot light.

Any idea how I can wire this so the alternator charges? I plan on upgrading to a high-amp later, but I need this to work to hold me over until then. I also read that this alternator may not charge if the battery voltage is less than 12 volts.

I tried the Mercedes board, but haven't had any replies.

Thanks

According to Alldata...

Both B+ wires go to the battery and the D+ lead goes to one side of the dash light. The other side of the dash light goes to an ignition source.

Not knowing what year your 4Runner is I can't look it up.

I looked up a "1985 Toyota Truck 4 Runner 4WD L4-2366cc 2.4L SOHC (22R)" and it seems to me like it would be simplest to add a light bulb under the hood. A 194 bulb (like for a marker light) would work well for this application.

According to Alldata...

Both B+ wires go to the battery and the D+ lead goes to one side of the dash light. The other side of the dash light goes to an ignition source.

Not knowing what year your 4Runner is I can't look it up.

I looked up a "1985 Toyota Truck 4 Runner 4WD L4-2366cc 2.4L SOHC (22R)" and it seems to me like it would be simplest to add a light bulb under the hood. A 194 bulb (like for a marker light) would work well for this application.

Thanks for the reply. I installed a small "marker lamp" with a 194 bulb under the hood. Are you saying the positive lead should go to an "ignition-hot", and the ground to the alternator D+ ?

It's an 89 4Runner. Thanks again for your time.

Roy

Yes. Positive and negative are irrelevant for a (normal) light bulb. Just make sure neither of them is grounded (like through the marker housing).

Basically if the alternator is not charging it will be a source of ground and the bulb will light from the ignition source when the key is on. If the alternator is charging both sides of the bulb will be at 12-14 volts and, having no ground source, it will not light. This is how the bulb lights when something goes wrong.

Thanks again for replying. Now I understand how it works.

Roy

ETA: For anyone else who finds this problem, I had to add an LED (diode) to the circuit, or the engine wouldn't shut down. I guess it was feeding back thru the circuit even with the key off. The LED solved that.

Thanks for the help guys.