Alternator field sense wire drawing current

[kabarakh]

Hello all,

 

My '88 GL has had a current draw for quite some time now, but as I hadn't been using it much i'd just unplug the battery till it was needed. Now that ive bent the valves in the impreza however, I've started to work on tracking down the draw.

 

Using my multimeter I narrowed it down to the alternator (maxima), which was very old and crotchety anyway so I replaced it with a remanned unit after reading that the diodes had most likely failed. Unfortunately with the new unit in I'm still getting draw, to the tune of 3amps.

 

I've narrowed it down to the field sense wire, but I'm not sure where to go from here. Am I best off tracing that wire all the way and checking for shorts etc, or just I just remove and isolate it from the plug and route it from the alternator somewhere else to get its voltage?

 

Thanks for any and all input!

[ANIM_Hooneru]

Hey Kabarakh,

When you say you have a draw on the "field sense wire", how did you come to that conclusion?

Did the current draw go away when you unplugged the connector from the back of the unit?

 

If that is the case, then the fault is within the alternator itself. The other end of the Sense line (S) is connected directly to the + side of the battery via a fuse, any short on that line would blow a fuse and leave you with (depending on alternator design) low or no charging, it wouldn't lead to a current draw. Same deal with the Field line (L), if there were a short on that line, the Battery Warning Light on the dash would be on all the time, and you would have no charging.

I would be taking it back and getting the person who reco'd it to check it out. Even if you get the vehicle to them, if you can prove that it is in the unit itself (which from what i've read so far, looks like it) You may even be able to get a warranty on it.

 

I know from my own experience (I am an Auto Electrician by trade) that workshops generally shy away from manufacturing Hitachi style alternators, they are a pain in the rump roast to do anything with the Regulator and Rectifier on account of the fact they are half riveted, half soldered together. Usually in the process of removing the rivets you wreck the plate. My guess would be they've ripped it to pieces, thrown brushes and bearings at it and called it 'reco'. Hitachi Rectifiers are notorious for going bad, and could quite possibly be the cause of your problem.

 

Anyway, let us know how you get on.

[kabarakh]

Yes, the current draw went away when the wire was unplugged. Ive tested it with my old maxima alt (3amp draw) my old oem alt (3amp draw) and my 'new' maxima alt from napa (3 amp draw).

 

I swapped the plug for two spade terminals years ago to ensure I could use any alternator that fit regardless of the plug style, which is why I know it's the field sense wire. There is no change on the draw when I unplug any of the others. Perhaps I've just got bad luck and all three alts are bad? I can certainly go return/swap it out and report back if so.

[kabarakh]

Well its definitely the alternator. After removing the field wire the draw disappeared, so I jumped the terminal on the alt to the battery stud on the back, omitting the field sense wire altogether... and the draw reappeared.

 

So tomorrow I'll swap out alts again and then report back.

 

Damned remanned units....

[DaveT]

try aspwholesale.com for alternator parts.

[kabarakh]

So I'm stumped again. Returned the remanned alt and replaced it, but I did have them bench test the one I returned and they said it passed.

 

Plugged in this new one and I Again have current draw. Is my luck really that bad or am I missing something?

 

Would an inline diode on the sense wire help? I can't think of anything else to do offhand, except maybe wire it to my ignition so it only gets voltage when the key is on instead of constantly.

[ANIM_Hooneru]

Hello again,

 

Putting an in-line diode will not help in this situation.

 

Can you upload a photo of the unit and your wiring?

 

The only other possible outcome is you have your wiring wrong which I assumed you had right.

 

I'm not exactly sure what you are referring to as 'Field Sense', as there are two Circuits into a Hitachi Style Unit, the "Field" Circuit, (which is identified by Terminals D+, DF, F, L) and the "Sense" Circuit, (which is identified by S) and occasionally an "Ignition" Circuit, (Identified by IG or R)

 

You need to test you vehicle wiring.
Have you got a test light handy?