Euro 85 alternator not charging, signal wire popping fuses
 

A friend's '85 euro can't keep 12v going to the charge wire to enable his alternator at start-ups. He's bridged the wire with another ignition source wire by the jumper plug in the engine compartment, but this weekend it started NOT charging again, & popped a few fuses.

Is there a universal "fix" to this issue? I remember a track car I used to have did the same thing & we bridged it w/o any further issues.

Thanks!

Mark

I think you need a resistor. The normal route is... ignition, though the charging "dummy light", or if that's blown there's a resistor on the back of the cluster, to the alternator (which is acting as ground). therefore allowing the light to light up. Once the alt. starts to charge it changes the ground to pos. (I have no idea how) and the light goes out because it's not grounded anymore. Now if you have a jumper wire without any resistance in there it's essentially a short circuit that blows fuses.

the bridge work may be the reason its popping fuses ,
I would suggest to remove the 14 pin connector cover at the hot post and inspect the wires for them touching and shorting out, look for shedding insulation.
Then do an inspection of the alt charge signal wire up to the dash.It goes through the 14 pin connector.

The blue signal wire usually shears about 4 inches up from the connection point at the alternator from letting it hang by the harness, its an easy fix once you find the break, also inspect the gauge cluster for the resistor being fitted and connected

Universal corrective fix
 

Hey Mark, When you say that you are now blowing fuses, you mean the fuses in the circuit that you’ve tied the alternator excitation circuit to ? Most people will recommend that you reconfigure everything back to the original circuit and troubleshoot from there.

The excitation circuit is only made up of a ballast light bulb (warning light bulb in the dash mounted voltmeter) in parallel with a small resistor on the back side of the instrument cluster. Check to make sure that both of these components are in good condition and the D+ wire is complete from the alternator to the warning light.

Usually the best universal fix is to replace the initial defective part

One other comment - if the ballast light bulb is burned out, the alternator will have trouble priming at lower RPM's (if it primes at all) to provide a charge to the battery.

Michael :)

it's popping the radio fuse most commonly. I'll check tonight. I might just run another relay & power the signal from that with an inline fuse.

Interesting. Where is this Ballast Light Bulb?

In the dash, the red light for the alternator.

Since I don't have my car. Does this have anything to do with the "!" bulb? If not, exact location of Alt bulb?

Inside the voltmeter, Leo :)

Tiny red lamp, right at the bottom of the scale..

Wow, so this little lamp completes a circuit? I wonder if this is in my OB too?

Does the "!" Bulb complete any other circuits as well?

Yes, same in our OBs and most Alt circuits.

This explains it.
Earliest cars had a bigger light & hence, no resistor.
When the light size was reduced, they needed to add the 68ohm resistor.

Not sure why radio fuse is blowing. Remember that the excitor wire runs through the 14 pin connector.

http://forums.pelicanparts.com/uploa...1290193127.jpg

Huh, I did notice that the bulb is out.

Great thread!

I was having problems with the Stepson, and found that I had connected the small wire at the back of the alternator to the wrong terminal in the back of the alternator. I fixed that and it solved the problem.

We replaced the resistor with a new 68ohm unit & replaced the odo gear as well, but the problem remains: alternator is not charging & the dash-lights are still lit up. What a bummer.

is the alt light also lit or out??
The alt light is at the bottom of the ALT gauge

All the dash lights are lit, alt light included. Alt gauge continues to show that it's not charging as well.

Did you trace continuity of the excitor wire?
It runs through the 14 pin, I think wire #1, blue.
Solder joints sometimes break under the covers.
But you are a 928 pro, you know this!

Uhmm....I own an '85 928S2, the same car as your friend. Are you 100% sure that the alternator is good? I suspect it has simply failed after 25 years of duty. Mine did just that last month, I replaced it with a good rebuilt unit from one of the 928 shops.

The failure symptom: I drove the car to a marina to buy non-alcohol gasoline for my boat [a subject for a post later...], and after filling the 5 gallon plastic container [fits perfectly on my front passenger floor], I went to start the car...but the usual set of illuminated warning lights in German stayed on no matter how hard I revved my engine. I knew what the problem was- the day before, I had had to rev the engine several times to get them to shut off. 25 years and 150,000 miles is a pretty good number for any alternator, so I didn't mind. I called a friend an alerted him that he might need to bring his car to pick me up, but I was only 4 miles from my house and I made it home after 20 minutes of traffic with no problems whatsoever. I have no idea how long a 928 can run off the battery, but it made it for 20+ minutes.

The alternator was easy to install, though there was the usual problem getting the bolt to go all the way through. It just took a bit of persuasion with a small hammer, and me holding the unit this way and that to get it to go through.

Take your car to Pep-Boys and have them check your alternator; they will do this for free, and you'll know instantly where your problem lies. While I would spend the extra $ to buy the new alternator from the 928 suppliers, you can probably buy it in one of those cheap shops rebuilt for less than $150.

Good Luck!

N!