The Darned Generator Light (Red)

In the last post, I remarked that I was getting some peculiar behavior on the generator light. It was coming (back) on at higher RPMs, but I can verify that the voltage at the battery was increasing as well. Normally, this would mean the light would be off.

This is all a little bit of an adventure at times. I am not an electrical engineer and have already shared that I never really clicked with vehicle electrics. Even so, I am not ignorant of electronic principals and can usually muddle my way through well enough. In that, you can read that I have never set a vehicle on fire from an electrical issue. Maybe that should be a certification on its own?

In this case, I have had to calculate how aftermarket charging components, lower on-bike electrical demands, and the aftermarket R21 system would all interplay. So, seeing the gen light on is not as straightforward, or at least not in the same way as stock airheads. It does the same thing and works the same way as it would if stock, but it is not wired as stock. The light appears to just be hooked up to an output from the R21, so there’s a little bit of fog around what happens inside the magic “electricy” box thing.

Turns out, nothing happens in the R21 unit for this. In this case, it simply passes the signal from the voltage regulator through to the generator light output and allows for a cleaner harness setup. After reviewing a lot of details for the charging system and what the various components actually do I began revisiting the setup on Red for the nth time. Seriously, I’ve lost count at this point. In all the cross reference work I had done, I found one thing in particular that I could not explain.

In this partial view of the NWT custom wiring diagram, we see a pink wire connected to DF on the voltage regulator. This lead is connected to the R21 as “generator/charge” sensor. Since my new, but admittedly still shaky understanding of the charging system was sinking in, I was curious why we would use the DF connection as one of the sources for the total system power which determines if the light is on or off. My understanding is that the DF connection feeds a portion of power back to the alternator to amplify the three-phase power generation by adding to the electrical field between the rotor and stator.

Comparing this to the more generic installation instructions from NWT for the R21, we see a different setup:

Here, we take the charge sensor from D+ which should provide the total system DC voltage after the diode board converts the three-phase AC to DC. As luck would have it, I had separately discovered that the wiring I used between the voltage regulator and the other charging components did not support the temperatures of the front of the engine with enough overhead for me to feel confident they would last, so I had already planned to replace them with higher temperature rated wire. I also have a spare diode board and voltage regulator, so I decided to move the R21 charge sensor to D+ when I swapped out those connections.

Viola! No unusual generator light. I think it came down to a simple error in the custom wiring schematic.

After a late evening test ride of about 5 miles, everything seemed to remain normal. I am taking this item off the punch list.