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I need so help from some of you more experienced guys. My serial number is MD 79080. Question 1 - What year is it. 1954 I think. Question 2- I need a wiring diagram for this jeep.It is a12 volt system and has an altenator with 3 wires comimg out of it. 2 wires go to starter, one wire goes to inigition switch (inigition switch on dash with key). Problem is alt does not charge battery. Yet when battery cable is removed (test for alt charging or not) engine keeps running. Alt must be good ,but not charging battery. I need a wiring diagram and info on how to wire a 12 volt altanator.

raydon01 wrote:I need so help from some of you more experienced guys. My serial number is MD 79080. Question 1 - What year is it. 1954 I think. Question 2- I need a wiring diagram for this jeep.It is a12 volt system and has an altenator with 3 wires comimg out of it. 2 wires go to starter, one wire goes to inigition switch (inigition switch on dash with key). Problem is alt does not charge battery. Yet when battery cable is removed (test for alt charging or not) engine keeps running. Alt must be good ,but not charging battery. I need a wiring diagram and info on how to wire a 12 volt altanator.

If I remember correctly, the wire going to your ignition switch is the "exciter". One of the other wires going to the + post on your starter (where the battery + cable is attached) is what actually charges the battery. The 3rd wire is usually used to run the "dummy light" on the dash. If not used for that, it's usually connected back to the post for the 2nd wire (which is essentially what you've got).

Off the top of my head, it's sounds like it's wired right (or, at least, right enough to charge the battery). Those older 3-wire alternators usually had to be revved up to a certain RPM to start charging, but if it runs without the battery cable connected, you are getting juice to the ignition circuit.

How do you know it's not charging? Is your battery going bad?

Okay, I got that a little mixed up. Read here:

http://www.expeditionlandrover.info/Del ... ators.html

There's a diagram about halfway down.

The reason I say it is not charging the battery is When I charge the battery ,the engine cranks over fast and cranks up fast. After I drive some or crank it up sveral times the engine cranks over real slow (like the timing is retarder, I do not know if it is or not .Havent checked it.)but it will crank up.

Is the serial number MD 79080 a 1954?

I have the dash plate for MD 78343 with a DoD of 12/54.

Thanks Warren. Thats makes mine a late 1954 but most likely 1955.

I am reasonably sure yours is a DEC 1954 unit. I have recorded serial 79060 as a Dec 54 and the earliest recorded Jan 55 unit I have is 79785.

Willys Military jeeps were produced on the calendar year not the civvy model year.

It is best not to guess or take shots in the dark with that alternator. It's correct wiring depends entirely on what make/model alternator is being used.

Either post a photo showing the make/model and wiring connections or post the manufacturer's make and model number.

Also, do not disconnect the battery from your system with any alternator installed. It can damage the alternator or it's regulator. That technique for troubleshooting a charging issue is used only on generators.

I suggest getting organized first by arming yourself with a wiring diagram of what you actually have on your jeep. Then make comparisons with a stock wiring diagram found in TM 9-8014 which is a free PDF download here on our downloads page. Next obtain a good quality digital VOM (Volt-Ohm-Meter) and review some basic electrical troubleshooting guidelines.
This is a good point to stop and find a friend that is familiar with this subject to help settle you in. A simple call to your local MVPA regional club will usually yield a name or two of the electrical smart guys in the group.

Lastly I cannot overemphasize the seriousness of fooling with an electrical system that you do not understand and resulting fires that can happen when blindly jumping, crossing and mixing wires. Wiring fires are not easily extinguished and many a jeep has been seriously damaged by such fires.

Thanks for your tip Wesk.

raydon01 wrote:The reason I say it is not charging the battery is When I charge the battery ,the engine cranks over fast and cranks up fast. After I drive some or crank it up sveral times the engine cranks over real slow (like the timing is retarder, I do not know if it is or not .Havent checked it.)but it will crank up.

That sounds like a bad battery. Do you have a place that can test it for you or do you have a different battery?

Could be a bad battery but it could also be incorrect timing which becomes a magnified issue when the engine is hot causing slow cranking.

Very good point Wes.

OK,, Raydon 01, we have votes for at least two solutions.

Let us know the results.

Education is what this site is all about.

I am trying to upload my photo of the john deere jeep. This one I needed a wiring diagram for.



Read my reply under Photo Album post.

It appears my altenator is working. It also appears to have a battery drain. When I charged the battery real good . It spins the motor great. Over nite the battery will drain. If I remove the postive cable over nite, The battery stays up. I drove around and cranked the motor several times today with sucess. I will remove postive cable every nite.

Do yourself a favor and disconnect the battery the safe way. Either install a disconnect switch or always disconnect at the negative cable. No chance for shorting out a wrench that way.

When you get tired of disconnecting the battery cable try troubleshooting the battery drain.

You simply disconnect the negative cable and connect a 24 or 12 volt, as applicable to your jeep, test lamp to the end of the cable and to the battery negative post. If the lamp glows with all switches turned off you have a drain somewhere. To isolate that drain remove one circuit at a time from your system until the lamp goes out and that circuit is then the source of your drain.

The common culprits are the main light switch and the starter's switch down on the starter.