Alternator exciter coil connection no voltage

[Seabhac]

I bought a 93 Eura Mobil Transit with a banana engine. Theres a new alternator in it but when I turn on the engine theres no power from the alternator and the red battery lght is on on the dash. I gave the centre connection on the connecting block on the alternator a tip of the positive from the battery to energise the exciter coil and it started charging and the light went out. I imagine I cant just give it a permanent feed from the battery but I was thinking a feed from the starter when the key is fully turned would do the job or is this not a good idea? I noticed what appears to be a diod on the loom with the same coloured wires as the wire connected to the exciter connector, does anyone know if this is part of that circuit? Maybe the diode is fried and needs changing? Any help would be much appreciated, Thanks, Ronan.

[Frag]

Are you sure the warning light wire (usually blue) is on the correct terminal ?
Has your alternator got the 3 studs for wiring ?
The inline diode will be to prevent charging voltage from warning lamp keeping ignition live when you key off,to prevent it back feeding

One of the 3 terminals is usually ‘half’ voltage so around 7 volts.
One is main Charging lead
Other is for warning light and should be pretty much same output as main lead,full charging voltage.

[Seabhac]

Here's trying to continue this conversation today. For some reason I was blocked yesterday because Ive been flagged as a spammer. No answer from Admin to a pm.

[Seabhac]

Thanks Frag, all wires seem to be in the correct place. No voltage on the exciter wire, I crossed that with Batt+ and the alternator charges and the battery light goes out. The lower voltage one seems to be around 500 mv or something strange. I pulled into a garage to check air pressure and the voltage has dropped because Id turned off the engine, I have a USB with voltage indicated in the cigarette lighter which miraculously climbed to 13ish volts on its own so there must be a loose wire. Probably the dash. The diode I mentioned in the first post is a temperature sensor. I tried to post pics but failed, illtry again. Thanks for all the help.

[Seabhac]

Trying to upload 3 photos again.

[Seabhac]

Pic 3

[Frag]

The D+ terminal /exciter wire (blue and white,centre terminal) provides a 12 volt feed,through battery warning light to excite alternator,so it’s a 12v feed to alternator,through the warning light bulb itself.
When engine is off,the bulb grounds through alternator so is illuminated,
Then when alternator starts charging and outputs 12 v from that terminal that puts the warning lamp out as it now has 12v to either side of bulb.
The diode is exactly that,it’s not a temp sensor.
It’s to prevent the alternator powering up the ignition circuit through bulb when you key off,otherwise van won’t switch off and ignition will stay on.

Also,nearly all transit 2.5di’s,battery light will NOT go off on first start,until you blip throttle or bring revs up
This is normal

[Seabhac]

I see indeed, I thought it was the diode but when I looked up the numbers it was being sold as a temperature sensor. I have a JCB 3cx that need a tip to the throttle also to put the light in the dash off. Alls good so and the battery is holding charge. I was worried driving ot home even though the alternator was charging if I had the lights on and was ticking over at the traffic lights the voltage was dropping below 12 volts, a tiny amount of throttle whilst waiting remedied this until I got going again.

[Seabhac]

Thanks for all the help!