85/86 ATC250R Race Harness Ground Location?

[ps2fixer]

I don't have access to one of these machines, where do the racers ground their harnesses at? I'd guess at the top engine mount bolts. My ring terminals are 6mm (about 1/4in) for the hole, not sure what size of bolt is used for the engine mounts though. I saw I had a request for the race setup (no lighting circuit) harness for an 86 250r. Looking over my template, it looks like a nice and easy harness to make besides that ground location problem.

Also if I could get a measurement to the nearest ground location, that would be great. Using the CDI connector would give me a good base line for length, like CDI wire + 3in to reach the bolt.

The OEM layout had the ground location at the tail light area, would like to move it closer to the engine area in this harness though.

I suspect the ground location on the 85 would be the same or atleast similar. It's hard to find good photos of these machines with the tank off so I can see stuff better .

Any help would be great. I'm thinking this harness I could make for $65 shipped.

I added a photo of a near complete one. That ground wire looks so out of place being so long lol (OEM length). The pile of wire in the upper left corner is how much wire the full harness has with all the lighting wiring.

[shortline10]

I believe the factory ground was located were the regulator bolts to the frame .

[bkm]

I've got an 86 I'm getting ready to pull the tank off of and can snap a few pics for you. You are correct that the ground is near the rear of the bike. You could make it ground at the head stay mount or where the radiator brackets bolt to.

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[ps2fixer]

Could you check the bolt sizes while you're in the area? My ring terminals measure ID 6.35mm, to go bigger I'd probably have to buy new tools and of course terminals. I suspect one of the side cover bolts could be an option but probably be a bit ugly. I'm guessing the head bolts are too big, not really ideal for wire to be by the hottest part of the engine anyway, but I do use high temp wire (105C rated).

Too bad there wasn't a dedicated ground pin like the 350x has at the alternator plug, that machine has that ground + a frame ground eyelet. Guessing part of that is because of the 200w alternator in it, the frame ground eyelet probably isn't need for just ignition.

Anyway, some photos would be a big help. A tape measure in the photo could let me use a photo editor and estimate lengths fairly well, just has to be fairly squared up photos, not at a huge angle etc.

[bkm]

My finger is pointing to the cdi location. The headstay bolts are 8mm. The closest 6mm bolt I could find is the radiator mounts. This bike is missing the right radiator bracket for some reason.

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[shortline10]

The factory ground lug is the std 6mm eyelet .

[ps2fixer]

The factory ground lug is the std 6mm eyelet .

Yea, most Honda's are, that's why I have 100s of them lol. Hoping to relocate to a closer spot to the engine though. The harness is for the race community, it seems they love short tiny harnesses.


@bkm

Thanks for the photos. With the radiator support bolt out, does the washer come off? The ring terminal would have to go between the bolt head and the washer to have a quality connection.

Little longer distance, but the photo of the left side of the engine has a black wire/hose ran though a holder. Looks about the right size to work well and it grounds to the engine (perfect for the coil/ignition system). I think I'd target that bolt if I was building a race machine and a harness from nothing. It might be on the small side (easy to snap), but shouldn't need a bunch of torq to get a solid connection. The threads and bold head face to ring terminal are the connection points.

Update, I've ordered 100 qty of the 8mm ring terminals. I suspect this isn't the only usage I'll find for them.

[bkm]

That is the throttle cable in the picture of the left side. That clamp is held on with an 8mm bolt. The radiator has a metal collar that would sandwich the eyelet between it and the frame. The only problem would be pulling the radiator off to slip it in there. If you could get 8mm eyelets, the headstay would be my location of choice.

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[ps2fixer]

I did a quick search and looks like if I used 14 gauge wire (way over kill), I can use an 8 mm ring terminal. Not sure if my crimper can handle it though, it's hard enough crimping the 6mm ones, it's like right at the point of being too much. They are thick terminals though, that's why it's hard to crimp. The random one I found is a bit expensive, but it's being sold per unit, instead of like a spool of them, so in bulk it should be similar priced I'd think.

Searched around the bulk suppliers and I think I found a suitable option. ID should be 8.3mm, and the wire crimp area is for 20-15 gauge wire. Only down side... min order 5000 units. Anyone wana throw $735 + shipping at this lol.

Found another supplier with a neat 3d model of it. 0.6mm thick which I'm pretty sure is the same as my 6mm ring terminals. Brand is Japanese (TE/AMP) which is common for OEM, so should be very good quality. I think this probably will be the best route.

Anyway, it wouldn't hurt to validate, based on my fancy photo editing with the tape measure, from the CDI location to the top engine mount bolt (one though the engine head) should be around 9.5in. Based on the wire routing diagram in the service manual, the CDI wires split off from the main harness right around the radiator (engine side), so it seems like if I made the wire around 12in long with the 8mm terminal, it should be a pretty good fit with a little wiggle room for mounting it to the frame and such.

You want to test fit the harness for me? It should be a useful thing to have around for you as like a bare min test harness encase you ever have issues that might point to a bad harness. Shouldn't be too hard to swap out (leaving the OEM one on), just plug in the CDI, bolt the ring terminal on, plug in the engine plugs, and have the kill wires in hand so you can short to kill (or a teather/kill button).

[Red Rider]

Little longer distance, but the photo of the left side of the engine has a black wire/hose ran though a holder. Looks about the right size to work well and it grounds to the engine (perfect for the coil/ignition system). I think I'd target that bolt if I was building a race machine and a harness from nothing. It might be on the small side (easy to snap), but shouldn't need a bunch of torq to get a solid connection. The threads and bold head face to ring terminal are the connection points.

If you're talking about the wire attached to the L side of the cylinder, via the wire holder, that wire holder is not supposed to be there. That particular wire holder should be attached to the upper, L side, reed cage, mounting bolt at the back of the cylinder. The bolt, that it is currently attached with, is a drain for the cylinder's water jackets.

[Red Rider]

Hopefully it will be evident in these 2 pics, what I'm talking about, without having to go take specific pics.

[ps2fixer]

Good to know, I guess not such an ideal bolt lol.

I'm thinking the top engine mount bolt that goes through the head is the best option, but maybe there's something near the stator connections to bolt it to.

Have to love doing R&D with out direct access to the machine.

[Red Rider]

I'm thinking the top engine mount bolt that goes through the head is the best option...

That's an 8mm bolt there, and it gets torqued to 18-25 ft.lbs.

Have to love doing R&D with out direct access to the machine.

Yeah, you've made it a bit difficult on yourself with this project.

Here is another possible grounding point. On the R side of frame neck, just forward of the radiator, there is a 6mm bolt for attaching a wire guide to, and as luck would have it, the wires run right past it.

[ps2fixer]

Ahh that looks like a good spot too. Looks like it might be a pain to run the wire to it though?

[Red Rider]

Ahh that looks like a good spot too. Looks like it might be a pain to run the wire to it though?

I assumed the wire would be protruding from the harness at the appropriate point to attach to the new grounding point. Or does that portion of the harness get eliminated on the racing harness, because of no lights?