Battery light stays on.

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woody5248

New Member
Posts
17
Location
Wiltshire
Help please,

I have a new alternator on my 90 300tdi. This has worked fine and still outputs 14.1 volts at tick over. Went out the other night and when I switched off the engine the charge warning light stays on even with the key out. When I switch the ignition on the light goes out and stays out when the engine is running. I have the brown and yellow wire connected to the small post of the alternator if you remove this the light goes out. Any help great fully accepted.

Best Mike
 
We know:

The connections to the alternator are straight battery connections plus a Brown/Yellow wire which is the charging connection.

The charge light gets an ignition live feed and a Brown/Yellow feed.

A bulb will light if it gets a ground and 12v connection in either direction.

So....

The ignition live connection will drop to ground when the ignition is off which means that the Brown/Yellow wire appears to be giving a permanent live connection. We know this because when your ignition is OFF the light is in and we know the ignition with be ground at that time. When you switch the ignition ON the light goes out i.e. 12v from ignition and 12v from the Brown/Yellow.

The possible causes of the Brown/Yellow being permanently live are..... The diode being shorted out, a fault with the alternator (unlikely if it is new) or connected wrongly.
 
cowasaki said:
We know:

The connections to the alternator are straight battery connections plus a Brown/Yellow wire which is the charging connection.

The charge light gets an ignition live feed and a Brown/Yellow feed.

A bulb will light if it gets a ground and 12v connection in either direction.

So....

The ignition live connection will drop to ground when the ignition is off which means that the Brown/Yellow wire appears to be giving a permanent live connection. We know this because when your ignition is OFF the light is in and we know the ignition with be ground at that time. When you switch the ignition ON the light goes out i.e. 12v from ignition and 12v from the Brown/Yellow.

The possible causes of the Brown/Yellow being permanently live are..... The diode being shorted out, a fault with the alternator (unlikely if it is new) or connected wrongly.
Click to expand...

How the hell can anyone understand electrics?!
 
cowasaki said:
We know:

The connections to the alternator are straight battery connections plus a Brown/Yellow wire which is the charging connection.

The charge light gets an ignition live feed and a Brown/Yellow feed.

A bulb will light if it gets a ground and 12v connection in either direction.

So....

The ignition live connection will drop to ground when the ignition is off which means that the Brown/Yellow wire appears to be giving a permanent live connection. We know this because when your ignition is OFF the light is in and we know the ignition with be ground at that time. When you switch the ignition ON the light goes out i.e. 12v from ignition and 12v from the Brown/Yellow.

The possible causes of the Brown/Yellow being permanently live are..... The diode being shorted out, a fault with the alternator (unlikely if it is new) or connected wrongly.
Click to expand...
Thanks, you were bang on. Faulty diode and US alternator.. Replaced today, problem solved.

Mike
 
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