97 VW T4 2.4 Diesel

[winchman]

Had the alternator professional rebuilt with top quality components last August. Had to be brought home by the AA at the weekend as it was flashing the oil light, when you turn the ignition on the Batt light doesn't come on as it should? When the engine starts it's not charging, cant see any damaged wires, going to look again tomorrow.
So where does the Blue and red alternator wires go to? Hoping to bypass them and if its the fault replace them.
Just for those who don't know the oil warning system checks two different sensors depending on Engine speed it gets from the alternator so no alternator output lights the oil light.
Can some one remind me how the charge light should work?

 

[Olderisbetter]

I've had issues on T4s with the wires on the alternator I think it was a blue wire and that dual oil pressure warning system almost drove me mad till I worked it out

 

[winchman]

I've had issues on T4s with the wires on the alternator I think it was a blue wire and that dual oil pressure warning system almost drove me mad till I worked it out

Any tips?

 

[Olderisbetter]

After months of messing about mine turned out to be a faulty pressure switch on the front of the engine down by the sump, there is a test method on t4forums https://www.vwt4forum.co.uk/threads/flashing-oil-pressure-warning-problems.109439/

 

[m_c]

From memory, blue is the warning light. With the ignition on, it should be almost at battery voltage if checked with a multimeter, and bring on the alternator warning light if grounded.
Red is a battery sense, and should be permanently at battery voltage.

If the blue wire breaks, the alternator won't start charging unless the engine is revved quite high, and might not even start charging at all, as ye olde alternators rely on the warning lamp for excitation. Without the warning lamp connected, you're relying purely on some residual magnetism in the rotor to kickstart the alternator.

 

[winchman]

From memory, blue is the warning light. With the ignition on, it should be almost at battery voltage if checked with a multimeter, and bring on the alternator warning light if grounded.
Red is a battery sense, and should be permanently at battery voltage.

If the blue wire breaks, the alternator won't start charging unless the engine is revved quite high, and might not even start charging at all, as ye olde alternators rely on the warning lamp for excitation. Without the warning lamp connected, you're relying purely on some residual magnetism in the rotor to kickstart the alternator.

Thanks for this I will try to have look today, I don't suppose you know exactly where the other ends of the blue and red wires go to?

 

[winchman]

Just back from a voyage under the T4.
The blue wire is showing just under battery voltage with ignition on, red showing nothing so checked back to plug above starter and finally to the conduit where it enters the cabin still nothing, so any thoughts on my next move?
How can I by pass this if its possible?

 

[Olderisbetter]

Just back from a voyage under the T4.
The blue wire is showing just under battery voltage with ignition on, red showing nothing so checked back to plug above starter and finally to the conduit where it enters the cabin still nothing, so any thoughts on my next move?
How can I by pass this if its possible?

The problem we had on the T4 was the wires in the ribbed conduit are prone to being rubbed through, My.mates T4 had and issue on the back of the dash clocks when his alternator stopped working I think it is well known on the T4 forums.

 

[winchman]

The problem we had on the T4 was the wires in the ribbed conduit are prone to being rubbed through, My.mates T4 had and issue on the back of the dash clocks when his alternator stopped working I think it is well known on the T4 forums.

If I can find the other end of the wire I can check this will try again later

 

[carbon]

This is a page from a 1992 wiring diagram for a T4 2.4D

The red charge wire from the alternator is connected at the terminal on the starter solenoid(30) then back to the battery it shouldn't enter the cabin at all. I couldn't find a wiring diagram for 96/97 specifically but from memory 96 wiring was similar to the above diagram. After 97 when it was a 2.5 TDI the wiring changed a bit in that the charge wire didn't connect to the starter rather it went back to the battery through a 150A fuse that is located in front of the battery.