Alternator excitation and the resistance - Defender Source
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  #1  
Old September 27th, 2017, 11:21 AM
xathor
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Nick
98 Discovery
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Join Date: May 2017
Location: Huntsville, AL
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Alternator excitation and the resistance

Everything is great with my Defender (1990 200Tdi) except the alternator. The alternator works if I spin it up enough, cross my fingers and hope that it self excites. Usually somewhere along my trip the alternator starts charging at high 14 volts. Strangely enough, the charge light never goes out. This leads me to believe that the sense wire coming off the alternator to the bulb is missing causing the voltage to never equal out on both sides of the bulb. Looking at the wiring diagram for this circuit, I assume that this is how it works as the circuit never really goes to ground through the bulb.

I can't seem to find any pictures of the wiring for this charge circuit behind the dash. I'm trying to return the wiring on my truck back to stock, as the PO's mechanic was definitely not an electrician. I'd appreciate any pictures of the stock dash wiring for the charge circuit that anyone has.

If I can't find the wire to fix the issue, has anyone had luck jumping a resistor across the terminals on the alternator. If so, what resistor did you use?

Thanks!
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  #2  
Old September 27th, 2017, 11:37 AM
OH+D
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Adam
1972 Series III
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Location: Bolton, Massachusetts
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Pictures probably wont help much. You need to start testing wires with the multimeter to isolate where the fault is. If the wire from the charge lamp to the alternator does not have continuity, run a new wire. This is called an overlay.

Also work checking the connector and connections at the alternator itself as these are frequently damaged/corroded.
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Old September 27th, 2017, 12:44 PM
xathor
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Nick
98 Discovery
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Yeah, I have no problem finding the fault... I haven't really even tried yet. Running a wire is no problem.

What I am wanting to do is restore it to stock looking. Mainly interested in pictures to find what other wires the run was bundled with, what connector did it have on the end... etc. Wiring diagrams don't really tell you these things.
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  #4  
Old September 27th, 2017, 01:25 PM
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Red90
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John B.
1991 Defender 90, 200TDI
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Registry
Disconnect the wire at the alternator. Turn on the ignition and check for 12V at the wire. If it is not there, follow back to find the fault. It first goes to a plug for the engine wiring loom. From there it goes into the main wiring loom. The diode and resistor are buried inside the main loom. The other end goes to the dash warning light cluster. The wires are all brown/yellow. Simply look for the brown/yellow wires. The color is not used for any other purpose in the vehicle.
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