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Old 02-05-2021, 10:58   #16
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Re: Alternator voltage high D1-20f

Originally Posted by CarinaPDX View Post
The yellow wire is the voltage sense for the alternator's internal regulator. The connection on the alternator is to a 1/4" spade terminal on the outside of the back towards the top, and the other end is connected to the battery connection on the starter solenoid. With the diodes the wire should have been connected to a battery instead of the solenoid. When you removed the diodes the wire could remain connected to the battery or back to the solenoid; leaving it disconnected is not a valid option.

The normal way for connecting an exhaust fan is to use the optional auxiliary relay. The relay is plugged into the engine's harness and should come on when the engine is started. Presumably the power for the fan is sourced from the starter battery through a fuse and the relay. The MDI should power the relay when the alternator starts to output current, which it senses with the brown wire connected to the "D" terminal on the alternator.

I advise you to dig up the engine schematics and confirm that the wiring is now back to stock, or get someone who knows what they are doing. While I think what I wrote above is correct it is your responsibility to confirm before proceeding. Mistakes here can have dire consequences...

First a question, this optional relay. What do you exactly mean by plugin to the engine harness? The MDI unit?

Did some checking for my own understanding. The fan which now comes on from the motor main circuit breaker is powered from an extra relay, C&S R10-2b5-1. It is attached next to the MDI unit on the port side of the motor.
My observation is that the signal cable is connected to + on the alternator and the "power" to the + on the start solenoid/motor. Hence not strange if it comes on since the alternator gets power from the battery when turning the motor main circuit breaker on.

The "voltage sensing" cable is connected back on on the alternator but not connected to anything. I tested connecting it to the battery but no difference.

Also checked the charging with the motor on and it behaved quite normally providing 14V+ and some initial current until the batteries were full. It seems that everything is working except for the fan which is always on. This probably worked before due to the diode. I might call a motor electrician to figure out the relay but lets see.

It seems that I would need to change the incoming signal to the relay to something which is only powered when the motor is actually running. But where do I find that?
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