# Rewiring a ford 3000 diesel



## charttn (Jun 30, 2015)

While working on some other systems, I bumped the wiring to the alternator and it fell apart from corrosion. So I got to learn about that as well. Since it is a diesel and all the lights had been removed by a previous owner, I decided to try and simplify the wiring harness. The way it came to me was with two wires coming out of a lucas alternator. (warning, at this point assumptions start and will build upon each other) One wire feeding current to the field and one wire giving current to charge the battery. Most of the articles that I found describing alternator issues refer to the ALT warning light even to the wonderful schematic that I borrowed parts from for the below picture. This one even stated that if you don't have a bulb you need to at least have a diode. Now, to finally get to my question. Why is a bulb or diode really needed? As far as I can tell, when I turn the key off, that circuit is completely disconnected. Some of the articles described that the bulb helped block a battery draining flow of current. Yes, the light helps you know when the alt is not working but I can also just put a voltmeter on the battery before and after cranking it and look for a difference (right?). Anyway, I am seeking opinion, from the collective experience. Any issues with the below wiring?


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## EdF (Sep 15, 2014)

hello charttn,

One purpose of the diode or small light bulb is block or significantly reduce feedback from the field winding to the ignition coil after the switch is turned off. Applies to gassers only. With feedback from the field winding to the coil, the engine will not turn off. Since you have a diesel, this does not apply. The diode blocks feedback, and the small light bulb reduces current flow below coil primary winding requirements.

Another purpose of the diode or small light bulb is to block or reduce battery drainage through the field winding after the engine is turned off. 

I saw a diagram on the internet similar to yours, but it included an ammeter. There was a wire from the "B" terminal on the alternator to the "2" terminal on the alternator. I see you have a dotted line for this wire. Is this an internal connection? 

I personally like to have the idiot light or gauge to know that my charging system is working full time.


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## charttn (Jun 30, 2015)

Thanks EdF,
Yes, the dotted line is my assumption that the voltage monitoring circuit is jumpered internal to the alternator. There were no other wires attached and from what I have read about one wire alternators, that is the way it should be. I am planning to rehook a volt meter back up to the switched leg of the key as it is an easy way to monitor. I am curious though, you said diode/light was to" reduce battery drainage through the field winding after the engine is turned off". When I turn the key off and stop the diesel, I do not think there is any connection between the field and the battery. Am I overlooking something or is that describing a gas engine again? Thanks for describing the coil/field winding relationship, by the way, that really helped.


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## EdF (Sep 15, 2014)

I recall reading that the field winding can slowly drain a battery over a period of 2-3 months. Your switch connection should stop that. Use your ohmmeter to check for a high resistance circuit to ground from terminal "F", Terminal "2", and terminal "B". Then you will know...

Have you checked your alternator? Fredneck, a frequent visitor and contributor to this forum, calls Lucas the "Prince of Darkness" because their equipment fails frequently.


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