1979 kz750 twin Wiring Nightmare

Hello all, I've been fighting with a 1979 KZ750 I got as a gift that wasn't running. The owner supposedly had it running until he swerved off the road after a deer scared the life out of him. However, several things seem fishy even though at first glance it would make sense (busted ignition switch, busted tach, leaking petcock, egg shaped light trim, dented gas tank), such as the LED headlight wiring not making any sense. and with a fresh battery in none of the electricals worked. SO, my plight gets worse: Ive been trying to order the right ignition and everyone I find so far doesn't look right in terms of the wiring. I have a 6 pin harness that only utilizes 5 pins for the ignition. I ordered an ignition switch that was supposed to work and it was just a 4 pin (nicely designed but obviously doesn't work). Can anyone explain how to wire this thing up with a 4 wire switch? OR perhaps just a kill switch so I can see if this bike even turns over?


I replaced the petcock and fuel lines, a new fuse box, got a new battery and confirmed the headlight does work directly to the battery but none of the wiring harness gives me any confidence in this bike. And this is my first bike. Electrical isnt too new to me as I used to be a guitar tech but, ignition systems arent my specialty. I have a spdt three tab on off switch I bought in case someone could explain how to get that wired in just to start it and test the engine before throwing any real money at this bike. The wiring schematic is perhaps the least impressive aspect of this service manual to me, so I can use any help possible. Thank you all.

Here is a thread with a minimal wiring for a 79 750 which may be of assistance, just ignore everything for the lights and you should be able to get it going.
kzrider.com/forum/4-electrical/172746-19...mattylight?start=200

Do you have a service manual and multimeter?

Yes I do, that's how I managed to understand the 4 wire 2 position switch reads continuous when red and black mate. And I downloaded the 1979 service manual. Im just not good at knowing where I can splice wires to keep both running without shorting.

Here's a link to a 1979 Kz750B4 twin simplified diagram.
www.kzrider.com/forum/4-electrical/17274...ght?start=200#463164

That should make it self explanatory how to install a generic switch. It is drawn showing the original switch modified to simply be an on/off switch, but you can just replace it with a simple toggle switch.

All you really need to make it run, temporarily, is the ignition system which is a basic points system. It can be done with one or two wires total from the battery... assuming you can kick-start it.

It turns out my bike is a 78 750B. Is the wiring still the same?

Berserker wrote: It turns out my bike is a 78 750B. Is the wiring still the same?

That makes it a 78 Kz750B3 twin.
The ignition switch wiring is a tiny bit different from the 79 Kz750B4 twin.
(I'm writing out the long designations so people viewing later won't get confused mixing up models.)

You can use the same drawing with a couple minor differences.
Just ignore the yellow wire on the ignition switch in the drawing.
The wire feeding the kill switch will be brown on the 78 B3 instead of yellow on the 79 B4.

Here's a 78 B3 diagram. It includes the electric start.
But you can use it to compare the differences between the 78 and 79 ignition switch.
(I realize you have an aftermarket switch so the factory switch wiring is not very critical for you.)
www.kzrider.com/forum/4-electrical/17274...ght?start=280#579749

Regarding switches. You should know not to use any cheap switches that are made with vinyl. They love to melt in the on position.
Use a metal switch if you can find a good one. Most are cheap and get flakey soon. Or you can get a heavy duty, high quality switch made of epoxy resin that will last many years, but they are not cheap.

Your best bet is to probably ohm-out the ignition switch you bought and figure out how to use that as an on-off switch.

Thank you.. Well find out shortly if she starts. AS for the switches, what do you recommend? All the metal ones I've seen look like cheap pot metal.

In the world of cheap aftermarket ignition switches for cars, yeah most are junk. They'll work, for a little while.

The ones designed specifically for KZ's are better, but they don't all mate up to every model. If you can find one that fits, I'd recommend that and splice the wires if you have to .

Simple toggles should be the decent epoxy or metal ones. Pot metal is ok, as long as the switch is manufactured decently.
You'd probably spend $20 or so through a reputable supplier like Digikey for a really good 20 amp toggle switch.

Z1Enterprises.com has an ignition switch with 6 pin connector for the KZ750 Twin models, but depending upon what year, you may have to do some re-wiring.

Z1Ent >> 1978 KZ750-B3 >> Emgo ignition switch 40-80600


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Thank you for the info. Now I’ve got another interesting bit here. It seems my carburetor came with a bit of confusion. Where that nipple is has no actual port it just perfectly fits into the blank hole and I can’t seem to figure out where to branch it to.

I contacted Z1 before I bought the switch I bought and they had said that I had to “do surgery” literally as vague as that.

Did you get the correct ignition switch for your application & how did you determine what 750B you have?
I would have thought the 6-pin would be a better match for a 5-wire ignition switch, but what do I know.
The B3 wiring diagram shows a 4-wire ignition switch, but the B4 is 5-wire.
Internet image searches = "KZ750-B3" wiring diagram & "KZ750-B4" wiring diagram.


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