KZ 400 76 vs 78 compatibility questions

Hi all,
My son has been working on a KZ 400 and has hit a roadblock in the electrical dept......he has a 76 frame and wiring loom, with a 78 motor implanted and when he went to look at wiring up the alternator he found 2 wires coming out of the 78 motor and 7 places to plant them into the 76 loom. Also he thinks the 76 has a rectifier but the 78 does not.
Does he try to get a new 78 loom or is there a way to modify his current one? Any help?

Depends on the models. What models do you have?

The 76 A, S, and D all likely had 3-phase, excited-field alternators. Those had separate regulator and rectifier, and the alternator had 4 or 5 wires. Three of them were stator wires (all three likely white or yellow), and one (or two) were to the field coil. Field-coil wire was usually green, and there may have been a black one as well.

The 78 B, C, and H all likely had 1-phase, permanent-magnet alternators. Those had a combination regulator/rectifier, and the alternator had 2 wires. The two wires were from the stator (both probably yellow).

Other 78 models may have had the same alternator/reg/rec as the 76 models.

The harnesses are not interchangeable, but it's not too hard to add in the necessary wires.

Not sure which 76 he has (motor vin# is unreadable) but what you said about the numerous colour wires sounds correct. The 78 is a B1 with the two yellow wires coming out of the alternator. What necessary wires would we add to make all this work Lou? My son was pretty excited with the B1 cause it comes with a 6 speed gearbox which the other models did not.

I did not know that about the 6 -speed gearbox. Interesting.

Actually, based on the way you are going (couldn't remember when I was typing last time) 78 motor into 76 frame, you actually have more than enough wires in the original harness.

Those two yellows on the motor are simply the output of the alternator. They are AC voltage.
You will need to buy a modern, combination, regulator rectifier for single-phase, permanent-magnet alternators. The original, mechanical regulator is not compatible (plus its probably long due in maintenance).

The new reg/rec will have 4 or 5 wires depending on how it is designed.

The original regulator and rectifier should be removed.
The original rectifier should have 5 wires. 3 yellow, 1 black, 1 red or white.
The orginal regulator should have 3 wires. 1 brown. 1 black, 1 green.

The two yellow wires from the alternator will go to the two yellow wires of the new reg/rec.
The red wire on the new reg/rec will be the positive output. It will connect on the harness to where the white or red wire on the old rectifier was connected.
The black wire on the new reg/rec will be the negative output. It will connect on the harness to where the black wire on the old rectifier was connected.
If the new reg/rec has a fifth wire, it should be brown. It will connect on the harness to where the brown wire on the old regulator was connected.

You will ignore, and leave unconnected, one of the three yellow wires at the rectifier, and the green and black wires at the regulator.

You should consider, however, how much are you going to alter the bike in general, in regards to taking off lights and gauges, and what condition the original harness is in. It's very unlikely the harness is in perfect condition. Then decide if it may actually be easier to just re-wire the whole bike rather than go through all of the troubleshooting of finding all of the other marginal wires.