Vh 304 style alternator wiring

[Asho88]

Hi all me again I got a random issue that has me absolutely puzzled! My car is a VH 253 running a VN v8 ecu and injection was going well other then the battery draining and a weird humm from the alternator. Decided I’d had enough fitted a new reg and adjusted the alternator now I have no dash light the ecu is wired separately to the body running only what’s necessary to power the ECU. I’ve tried multiple alternators with no luck until I quickly tried an old 308 that works weird… it lights up when earthed. When the car is off the brown wire acts as an earth when switched on it’s seeing power this has me stumped any ideas?

[VTXU8]

Weird. The Brown wire should be earthed when engine is off or just ignition on. 12v+ to the light comes from the dash. When engine is running and ALT is charging the Brown wire will be isolated from GND making dash light go off. The brown wire may then see voltage if the Radio Interference Suppressor is faulty or wiring to it is damaged.

The other thing that comes to mind is being a VN style ALT. You may need to solder a Resistor on the + and - side of the dash globe. Without it, it may cause + power feed to the Brown wire which the Alt. may not like.

[Charlescrown]

I assume its a Bosch unit. The light should turn on by earthing thru the voltage regulator and when it starts charging and the output equals the battery voltage the light goes out so no dash light could be a bulb fail or wiring between the bulb and the (what you call the brown wire) regulator or a faulty regulator. Disconnect the brown wire and see if it measures 12 volts open circuit if zero you then need to do some wiring checks if 12 volt earth the brown wire and if the light turns on its a regulator problem.
In this diagram the light wire is shown as blue.

[immortality]

Weird. The Brown wire should be earthed when engine is off or just ignition on. 12v+ to the light comes from the dash. When engine is running and ALT is charging the Brown wire will be isolated from GND making dash light go off. The brown wire may then see voltage if the Radio Interference Suppressor is faulty or wiring to it is damaged.

The other thing that comes to mind is being a VN style ALT. You may need to solder a Resistor on the + and - side of the dash globe. Without it, it may cause + power feed to the Brown wire which the Alt. may not like.

I remember vaguely that when using a VN or later style (2 wire) alternator you need to change the bulb in the dash for the alternator to a lower wattage.

[onslaught]

I have a bosch 85a on my mingswood and I'd have to check but I'm sure the charge light should be less than 2w.

[Charlescrown]

Most charge lights are low wattage. No need to be high as they work on a voltage differential. As I said just disconnect the D+ and earth it and that will tell you if there is a circuit/wiring problem.