OK guys ... I've been watching this thread for a few weeks, and have kept quiet up until now. I am an electrical engineer (who doesn't work for Yamaha) and here is my take on this.
The reason why the '06 bars work with the '07 harness is simple as Machzed orignially posted. Because the '07 harness puts them in parallel, thus increase the power used by each grip.
The reason this doesn't work with the '07 bars is because the heaters used by the '07 bars have a greater resistance to them. The amount of power used by the '07 grips wired in parallel is almost equivalent to the power used by the '06 bars wired in series.
The reason Yamaha did things this way was because they thought the problem with the cold bars had something to do with the solid aluminum hooks. They therefore made a bar that had the hooks integrated and then used a longer heater element. But the power usage stayed the same. Turns out they were both right and wrong. The aluminum hooks did act as heat sinks. So by getting rid of them they made an improvement, but they still needed more power.
Now regarding the issue of burning up the CPU with doing the '06 mod with the '07 harness..... I personally would not do this as Yamaha as indicated that the extra current draw through the CPU will cause damage. And here is my explaination why. I'll try to keep this explained as simply as possible, so try and keep up.
The voltage source to the grips is a 12V source. The adjustment of the grips is not made by simply varying the voltage. The grips work by a step signal source. The voltage source is actually alway 12V, but it is in a sense turned "on and off". When the grip setting is low, the on and off occurs slowly. When the grip setting is high, the on and off occurs more quickly, thus resulting in more heat. This is controlled by something similar to a 555 timer circuit in the CPU. Because the source is stepped to control the heat, the 12V is never changed. And since the 12V never changes, the amount of current draw never changes. And this is why Yamaha is probably not recommending this change due to the current draw.
The only way to get around this problem is to wire the '06 bars in parallel, then install a resistor in series with the paralleled grips. This will reduce the total current draw through the CPU. It will however reduce the power going to the grips. But you could size the resistor so that the grips still put out adequate heat when set on high. However, this still may end up in too much current drawn through the CPU.
You can see what I mean in the pics attached below. I took an scope and measured the source signal. You can see when the grips are set at low, the signal has a slower setp than when it is set at high. But the voltage remains at 12V all the time.
Do with this information as you like ..... But that is just a lowly engineer's opinion.
