My 1988 E-150 is discharging batteries with key off. The alternator light does not come on when I turn on the key with a fully charged battery in place.

I found a green wire with 14ga fusible link at a junction close to the positive battery post. There is a 3.8 amp current drain from this wire through the battery to ground. Is this the field wire for the alternator and if so, what does the current drain? New alternator needed? The one on the van has less than 500 miles on it. PM me at halka@hughes.net

Any help will be appreciated!

 

disconnect the negative battery cable and put a test lamp between the (-) terminal and cable. If the light is bright, disconnect the alt. connection and try again. If the light goes out then that means most ->likely<- the zener diode is blown in the alternator.

do this after the van has not run for a while to avoid sparks near a freshly charged battery.

 

Thanks. I have been trying to find the alternator connector, but can't see the rear of the alternator or down behind the battery. Can you tell me how many wires go to the connector or where it goes or how to find it or the wire color codes? I do see one big connector with two heavy wires. Would the green wire I found with the current flowing be the only hot wire going to the alternator? My Chilton's manual is almost worthless as far as wiring diagrams go.

 

First, is that wire you found a hack?

It sounds like someone wired a wire to the field winding directly, bypassing the ignition.

That is a tried and true way of doing it --- when you have a wiring fault in the harness that you cannot trace.

 

Is a "hack" an add on? No, the green wire with the current flow has a factory fusible link and is 14 ga. It connects at a big junction with other hot wires just forward of the battery. I need to find the alternator connector, but don't know what it looks like and can't see the back of the alternator so I can trace it. I understand these alternators have internal regulation.....correct? My Chilton manual lists an Autolite Alternator color code as "green" for the 4.3 amp 60 amp output unit used on 1981-1988 vans, but I don't know if the color refers to the wire color.

 

There should not be current flowing to alternator field windings with the key off.

 

> can't see the back of the alternator so I can trace it

Should be visible looking up at it from under the vehicle. I would tell you for sure, but, it is raining cats and dogs. Should be able to see it from the doghouse too.

 

OK just now I started her up and turned on bright lights, blower, and radio. I measured 17.3 volts across the battery.

Then with motor running, but lights, etc off my test light glowed fairly brightly when inserted between negative battery post and negative cable. I measured 1 amp current here but that measurement seemed a bit strange as it said exactly and unvariably1 amp regardless of polarity of the leads and the motor rpm increased slightly when I put the ammeter in the circuit.

Then with the key out, I remeasured current between the green wire that I think may be the alternator field and the positive battery post. Same 3.8 amp current leak regardless of whether the cable was hooked to the post or not.

Am I getting anywhere?

 

OK I took the alternator off and have it in hand. The green wire with the 14ga fusible link where I found the current leak has quite high resistance (~156Kohm?) to ground. I still cannot find out where it goes but it seems to be part of a big harness going under the right side of the engine toward the heater area. There were no green wires on either the regulator or output connectors (both 3-blades) on the alternator.

Are there any tests I can make on the alternator? It is a Motorcraft E73F-10316-AC
on the regulator cover and there is an arrow pointing to a screw to the "F" terminal that says "Ground here to test." There is no resistance from that screw to the alternator case. Alternator looks like new as it should as it was installed last August and the van has been driven less than 600 miles since then.

 

Yep field was grounded to the case. Hope the new one does not develop the same problem.

 

OK I installed a new alternator. Now have 14.96 volts across battery under load and a tiny 0.01 amp discharge from battery to ground. But I have no dash lights with key on except basic panel illumination, and brake. Check Engine light is on.

What should I check next?

 

Don't you have to reset the PCM to remove the error codes and clear the c.e.l.?

 

I don't know. Is that something only a Ford dealer can do?

 

I think most auto parts stores have a code reader that they will lend you. Ask them how to clear your codes.

 

Chances are you fried the light bulbs with 17V or more.

See link below for complete rebuild...

Try a reset of the computers first... see below.