1975 GT250 wiring madness

[MarkH]

Hi,

First time poster (I've been following the boards for a while though). Also wanted to thank oldjapanesebikes for assisting me with the gas cap seal.

At any rate, I've been doing a frame-up restore since mid-February (started a blog about it at http://www.machinesofman.com...although I'm playing catch-up on it).

I knew the wiring was going to be a challenge going back together (after I opened up the headlight bucket the first time). I ended up purchasing a NOS main harness as the old one was pretty ratty.

First thing I noticed this weekend, the old wiring harness has kind of a mini-harness in the headlight bucket that is plugged into the main harness - thus the old main harness doesn't have quite as many connections as the new one. (I'm hoping some of you guys have seen this too) - I'm trying to understand if the new harness can replace this mini-harness that's attached to the old factory one - sorry if I'm being vague, I just have no experience with these harnesses.

So, I made my first attempt to hook up the new (NOS) harness. The area by the battery seemed pretty straightforward to hookup.

I kind of just dove into the headlight bucket area after that. First tried to incorporate the old mini-harness to the new main harness - things kind of matched up, but not totally. So to simplify my tests (I do have a wiring diagram in the 250's Haynes manual) - I removed the mini-harness and attempted to just get something working, like the horn or the dash lights. This is when I just hit a brick wall. Nothing would power on (I did have the ignition switch wired using the 4 port block...as well as the 9 port block to the main harness).

I used my multi-meter to verify the ignition switch was working properly (it was). I also verified the main harness had 12v power at the headlight bucket (it does). And verified the horn button completed a circuit when pressed (it did).

But when hooked up, and the key is on, I get no response from neither the horn nor the dash lights. (I also put the horn on some exposed metal - as I wasn't sure if it needs a ground).

Everything was working when I started the restore.

So, I guess what I'm hoping to understand is this this mini-harness and why the factory harness and the NOS harness are a bit different at the headlight bucket (the part number of the NOS matches the number I see on parts diagrams - so I'm guessing there was a revision).

Second, maybe someone could help me (via baby steps) on just getting something to work - because then I think I could build on that.

Finally, the battery fuse is intact (I even replaced it just in case).

Thanks!
Mark

[MarkH]

I'll take some pictures after work to show the difference in wiring harnesses as well.

[MarkH]

Back again, here are some pictures (with comments) - I'm hoping for some enlightenment!

Hmmm, "Sorry, the board attachment quota has been reached."

Well, I knew the blog was worth something! I've posted my descriptive pictures there for you guys to see (it's just the first post, you can't miss it).

http://www.machinesofman.com/

[jabcb]

There may be some key differences between the wiring diagram in the Haynes manual and your bike.
For example, early T250s have a 4 position ignition switch (off, on, on with lights & parking) and later T250s & GT250s have a 3 position switch.

This diagram is from a Suzuki wiring diagram manual & is for a 1977 GT250.
It differs from your bike in that it has a voltage regulator & your bike doesn’t.
download/file.php?id=826

Compare the two wiring diagrams to what you have.
Hopefully it will resolve some of your confusion.

[MarkH]

Thanks, I'll study the diagram. It does look very similar (at first glance) to the Haynes manual.

By the way, what is the "Parking lamp" bulb (right off of the headlamp)? I don't recall seeing a bulb anywhere on my machine. Although, if it's optional - that might explain why my NOS harness has a single green wire coming off of the nine pin block (that matches the other side's block where the brown wire is coming in...I see that the brown wire on the diagram goes to the parking lamp).

You can see that green wire in my photos (it's on the right side).

[MarkH]

After studying the diagram more, I got some results!!! Thanks so much. Check out my site (above) for some "proof" pictures.