Any help ?
The battery light comes on that stays on after a alternator recon and battery change

it come on 10-20 secs after start up then turns heated screen etc off still charging the battery around 14.5  volt’s

their is a signal (from the small wire) going to instrument cluster 

Sounds like alternator is ok if you’re still getting 14V at the battery. May be worth checking earth connections etc in case something there means the 14V is dropping by time it’s picked up by the ECU or GEM module. 
 

Not sure if the problem with water ingress to GEM/passenger fuse box can show up as battery warning light coming on. 
 

When my month old refurbished alternator died was only getting 12V at battery

Diagnostic Trouble Codes from the OBD could probably give a better interpretation of what is happening.

If I couldn’t get the dtcs read for free, I think I would slap the dash above the instrument cluster when it occurs and see if anything changes. If it does, then it could be the solder joint issue within. Then check for dampness in the gem/BCM as mentioned above. If all seem good, then try to gets the dtcs read. Simplest and least cost checks first.

Thanks for both replies, their is continuity across all earth cables and  I have tried the bang on dash and had the cluster out to check it nothing obvious , also didn’t notice any moisture or damp in the fuse box area but I will double check over the weekend.

Nothing shows on obd test as it doesn’t put the management light on just the battery, can over charging cause the light to come on.

 

The dampness in the gem/bcm area usually affects the plugs into it just behind the glovebox. Generic code readers and some cheap elm327 adaptors fail to read all the dtcs  through the obd . Most guys use Forscan software (free) with a recommended adaptor .

39 minutes ago, Hawk85 said:

can over charging cause the light to come on.

It can, and it should be easy to check with a Multimeter, alternatively FORScan should be able to Live Monitor Voltages in the various Modules.

I did have an overcharging problem a long time ago in an older car because the Zener diode was faulty but the symptoms were different, the Charging Light would glow lightly at higher speeds only. I doubt modern Alternators have Zener diodes now so the symptoms are likely to be different now.

 

Is Fuse 31 OK ?

"Smart" (?) charging

Used the Delphi ds150e and laptop checked live readings just said battery ok,

although did say some things not supported

I might be able to borrow forscan see if it’ll show any different. And check the plugs/sockets behind the fuses.

the preface mk2 st’s/rs’s don’t have smart charge system 

 

You can do a basic test of the Smart charge system.

Disconnect the smart charging plug from the alternator and start the engine. With the engine at a fast idle of approx 1200RPM use a multimeter and measure the voltage at the battery terminals. It should be between 13.4V and 13.6V. Then reconnect the smart charge plug and repeat the test again with the engine at 1200RPM and the voltage should be between 14.4V and 14.8V

If the alternator passes both of those tests then the Smart charging circuit is working correctly.

Now you can do a load test of the alternator with the engine running at 1200RPM turn on the heated front and rear screens and the headlights. The voltage measured at the battery terminals should not be less than 14.2V

If it is less then you either have an alternator fault, or the main earth between the chassis and the engine is faulty and is either missing or high resistance,

11 hours ago, Hawk85 said:

the preface mk2 st’s/rs’s don’t have smart charge system 

I was referring to Diagram 2 in Haynes, which unfortunately does not cover my ST either !

Back to your first post, it sounds like the ECU/Gem does think that Battery volts are low, so turns off screens, indicating that with the battery light, and then increases alternator output ?

Where these the same symptoms that caused you the recon the alternator, and change the battery ?

Pre smart charging days, the initial excitation current for the alternator was through the battery light, so that the lamp would illuminate before cranking and starting, then extinguish as charge voltage = battery voltage, with no resultant current through the lamp.

 

 

 

This picture from garage that done alternator never have I seen this most garages would have maked sure it’s sorted properly 

 it was intermittent now it’s consistent starts light goes off 10-15 secs later back on 

Going to get the plugs out back of ecu and fuse box make sure not damp 

 

 

So the long and the short of it is, the alternator repair was a bodge job and the garage knew that.

I'd be going straight back to the garage and telling them to get it sorted.

The company that half repaired the alternator has quite poor reviews. https://www.yell.com/biz/forth-auto-electrics-dunfermline-535818/#reviews

Basically aye they took money and shrugged it off it was my mate had payed for it before I baught it he’s no into cars much aslong as the drive,

I baught to use it while I do some more work on my orange 1,

I hate any lights on dash 🥺