Another alternator woe

[mdav1970 31]

Hi Guys,

I've seen a few alternator woes on here latley sp hopefully someone will have an easy fix for me....

Seemed the battery was not charging enough to start car and as it was over 3 years old changed it for a higher cranking battery. Now new battery only seems to sit at 12v ish, so decided to go for a new alternator instead of 2nd hand. Still i only get 12v at battery. It starts fine and shoots straight back upto 12v ish and seems to sit there? i have type 7 alternator from the picture, with a 3 pin plug, 2 thin brown wires and 1 thick one. 2 of the wires have a 12v supply and the other seems to have nothing....but i also have power at B+ from the back of the alternator which i dont have a wire for? This is baffling me, so any advice would be grand...oh and i've treid reving it to ablove 3000 rpm makes no odds, and i don't have a battery light as i run a digital dash. thanks

 

[alanrichey 239]

Most alternators need the warning light connected to provide a current to excite the windings during start.  If it is not connected the alternator will never start.  So put a bulb from the ‘l’ connector to a 12v ignition switched supply.  Doesn’t have to be visible, although it means you will never know if the alternator has failed.

[mdav1970 31]

So the "I" as in ignition connector...do i turn on igniotion without starting car to see which of the brown wires it is?

 

[mdav1970 31]

Not sure i get you...which of the 3 wires from the alternator do i put the bulb if i have 3 brown 2 with power from battery?

[alanrichey 239]

You said you had a Type 7, so it’s the wire from the pin labelled ‘l’ on the diagram.

[mdav1970 31]

This is the back of the alternator. I've only ever had the 3 pin plug in the back, no other wires..

[fry61 1,260]

As Alan said & your picture shows --- ignition live to warning lamp ( 5 watt tungsten filament "bulb" (( american )) or lamp ) to B. 

Ignition on -- lamp should light --- fire up engine -- lamp goes out & voltage to battery should be close to 14 volts.

It's no good using a LED -- not enough current flow to get the alternator excited.

Edited March 15, 2019 by fry61
Added information.

[geordie40 39]

Both Bob and Alan are right, my alternator was only at 12v till I put a bulb in parallel with the led warning light on my dash rebuild and then hey presto 14v

[IanS 55]

Lets not forget the wire that is not shown.

The negative of the battery (earth) needs a good connection to the alternator.

This is often the mounting bracket to the engine and an earth strap to the battery and/or the body of the car.

Painted engine blocks, alternator mounting brackets etc. mess up the return path.

Try a wire from the earth post direct to the battery -ve.

[mdav1970 31]

Just check earth post to battery / engine and that makes no odds.

So ive traced the warning light wire a brown and yellow one...from the back of the alternator to the old plugin for the old ford dash, which has never been connected to anything for a couple of years. This wire shows nothing at idle and then shows a few volts as you rev it. So i need to just put a bulb from that wire to earth? What type bulb is best?

[fry61 1,260]

5 Watt 12 volt lamp & connected to IGNITION LIVE -- its purpose is to energise to alternator coils --- it will (should) go out as soon as the alternator is producing more than 12 volts

[mdav1970 31]

When testing the wire it shoots to about 0.24v if I rev it high, is that all it should be doing, doesn't show enough to light a bulb

[mdav1970 31]

Ahh not just to earth, right ok I will try it again....

[geordie40 39]

This little diagram helped me sort mine out

[mdav1970 31]

Fixed....I shouldn't have been such a pessimist...just that I never needed a battery bulb before I renewed the alternator.. same model & everything..

Had to change my wing indicators to clear ones anyways as I had a pair for about a year or so, so used one of the old ones for the bulb holder for now and shoved it behind the dash until I can arrange something better...

Again ..thanks everyone for all the advice....