Is this 911 alternator wired up correctly?

[Gary71]

Having just rebuilt the engine the alternator light stays on with ignition off, and goes off when I turn the ignition on.

I can only think I've connected something wrong. I lost my reference photos due to a iPhone cock up, so I went with some photos I found on line.



Any ideas on connection or other reasons for my odd lights are gratefully received!

[Nick Moss]

I don't think you should have an earth attached there. What is the marking where it's attached?

[chris68]

B+ on the alternator is the main rectifier output and connects to the heavy positive cable from the starter motor (which in turn goes to the battery).

D+ on the alternator is the field winding supply and connects to D+ on the regulator with a red wire.
There should also be a blue wire to the D+ terminal on the regulator which is fed from the ignition warning lamp.

Df on the alternator is the field winding terminal and connects to Df on the regulator with a black wire.

D- on the alternator is the low side of the field winding and connects to chassis with a brown wire.

Note, colours are from my '68 wiring diagram but don't think they will have changed.

Hope that helps. Happy to drive over if you need, could do with a drive out .

Cheers
Chris

[chris68]

some more thoughts ...

The ignition warning lamp should be fed with 12V from the ignition switch. The other side of the warning lamp goes to the D+ terminal of the regulator via a blue wire.

When things are working normally,

- With engine not running but ignition on, 12V is supplied to warning lamp from ignition switch. Current flows through warning lamp, regulator and alternator field winding. Hence, the warning light is on.

- With the engine running (ignition on) the alternator produces a field winding supply. You've got roughly the same voltage on both sides of the warning lamp so it's off.

- With the ignition off (engine off) you've got no supply to the warning lamp so it's off.

Sounds like the wiring to the warning lamp and from the warning lamp to the regulator could be the problem.

[KS]

Nick is right - the earth is wrong. You have the SEV-Motorola alternator, the same as mine. This is the correct wiring diagram.

[Gary71]

Thanks to both. The brown wire was in the wrong place, should have been on D-. However now I've corrected it the light still behaves the same.

Have I killed the diode pack or something?

[KS]

That is possible. If you have a spare regulator, try fitting that first of all. The way to check the diodes is to see if there is a drain back to earth through the alternator when everything is off. The diodes act as a sort of one-way valve to prevent this - when they fail, the alternator will still charge when the engine is running, but the battery will go flat overnight.

[Gary71]

Thanks Keith, think I may have fixed it, although I haven't checked if it's charging yet.

I had two errors, one the wiring as above and the second missing out the insulating washer under the main +ve feed.

Light does what it's supposed to now.

[KS]