Alternator Wiring

[itllbedonesoon]

good afternoon,

 

ok, Got a ford DOHC alternator onto a pinto with carbs using the VG wiring. I did a quick forum search and now know which DOHC alternator pin does what however: The VG alternator wiring had a 3 pin plug that was not compatable so i leaped in with both feet, gave it the chop and in the bin it went. Now i cant remember which way round the VG wires went???

 

Info i have is Alternator (viewed from above):

Large left pin - charging circuit

Middle pin - Dash light

Right pin - Auto choke

 

I have got VG wiring:

Large bn (i assume) to DOHC Large terminal (left from above)

Small Bn:

Bn Yl:

 

Any guesses on the 2 blanks????

 

also the auto choke wire would be handy to connect to my carb, but there does not seem to be one allocated in the VG wiring and which ever VG wire it is off the alternator just dissapears into the loom, any clue where it goes, where i can pick it up?

[itllbedonesoon]

Well i followed the wires back from the VG alternator plug and:

 

Bn Yellow = dash light

smll Bn = this just follows the heavy Bn and goes to the Starter motor terminal.

 

So i have disconnected the smll Bn and re-routed it to the auto choke. Although i did not have time to turn the engine on to see if it still works.

 

I have no idea how the charging circuit is suppose to work but this now look as though i have

1/ a heavy feed from Alternator to Battery +ve via starter motor.

2/ wire to dash display

3/ Wire to carb auto choke

 

Is there not suppose to be a -ve connection somewhere in there to make the alternator circuit work?

[Guest allenr03]

My alternator has two wires connected as well. A small brown/yellow wire which is the warning light and a thick brown which goes to the battery. There is a third terminal on the alternator which isn't connected to anything. I had the same thought as you about an earth. When I firts fitted a charge warning light it wouldn't go out. I thought the lack of an earth was the problem so I used the other terminal to earth the alternator. WHen I started the car smoke poured from the alternator and I was lucky enough not to cause any permanent damage or start a fire!!

 

I removed what was left of the earth!

 

The warning light issue was to do with the way I had wired the light up (I'm using Separate dials and warning lights.) I can't remember exactly how I did it but it involved a suppy and a diode!! The diagram is in the Sierra Haynes manual. Everything has worked fine ever since.

 

Rich

[TonySuperSpec]

Hi all

 

Just to clarify the alternator...

 

An alternator is bolted to the engine, since we are dealing with a -ve earth system the alternator casing is earthed and therefore ever thing including all the terminals are referenced to that earth point.

 

Within the alternator the voltage is A.C. unlike the older Dynamo's that produced D.C. The replacement of the dynamo with an alternator was for efficiency dynamo's output used to vary a lot and you needed a voltage regulator built into the loom to get a decent output.

 

When running at above 1000 r.p.m most alternators produce a voltage of around 14.4 volts. This can be tested at the battery terminals proving that the charging voltage is > than the unloaded terminal voltage of a 12v lead acid battery.

 

A diode block to rectify the alternator output is built into the termination wiring of all alternators so we get D.C. at the terminals.

 

Brown large wire is always the feed back to the battery for charge. The warning light is simply controlled by a diode that has the unloaded battery voltage on one side and the alternator output voltage on the other if the alternator voltage is > than the unloaded voltage then the diode blocks flow and the light goes out, otherwise i.e. when you switch on the igition but alternator is not spinning the diode conducts and the light comes on.

 

If the alternator fails to produce output this is the same as when the engine is not spinning and the light is on indicating a fault. Note you can get a fault if the diode termination at the alternator fails even if the alternator is working since without the diode rectification the voltage seen by the warning light diode is A.C. and no blocking takes place.

 

 

I strongly advise that if you have shorted the alternator terminal to ground even if the ground wiring melted, it will since most alternators can drive > 60 amps then you get the alternator and diode termination tested, although all may seem well the alternator windings will have been subjected to a current surge far beyond design limits as will the rectifier diodes.

 

 

Hope this helps power electrics in cars is quite dangerous in fact more dangerous than 240 v at home since a battery can produce > 50 Amps at 12V if you short it out and D.C kills so be careful

 

Cheers

 

Tony G