I my motorcycle's junction (fuse) box broken?
August 26, 2010 11:50 AM   Subscribe

I spent 4 hours circuit-testing my motorcycle's starter system. Everything seems normal. I suspect the junction (fuse) box is faulty ... right?

You helped me reinstall the starter solenoid on my 1993 Kawasaki Ninja ZX600C, but now something else in the starter circuit is acting up.

Pushing the starter button (kill switch in Run, transmission in neutral, kickstand up, battery charged) gets nothing: no cranking, no clicking, no nothing.

I thought the starter switch might have failed, so I checked it with my multimeter: it's fine. So I checked all the rest of the starter-related wiring I could get my hands, er, probes on, using the Haynes repair manual's diagrams as a guide: everything seems correct.

When I jump the terminals at the starter solenoid, the starter will turn and the engine will fire.

The kill switch is operating normally.

The running lights, headlights, turn signals, brake lights, and instrument cluster are all working correctly.

The battery's fine, and everything's grounding correctly.

Frustrating, until I remembered two other points I'd neglected:

1. The horn quit working at the same time as the starting system. I checked the switch: it's working normally.

2. The junction box used to click momentarily when I depressed the starter switch. It doesn't now.

So here's what I'm thinking: the junction box has failed. Does that sound logical? Likely? I could just order another one and find out, but Kawasaki wants $150 for a new one, and even eBay doesn't get better than about $50 for a used (i.e. questionable) one.

(And yes, I know I could ask this question at one of the motorcycle forums, but AskMF folks tend to provide more useful responses than the average 18-year-old forum trolls.)
posted by fracas to Travel & Transportation (8 answers total)
2. The junction box used to click momentarily when I depressed the starter switch. It doesn't now.

If it used to click, but now doesn't, that probably indicates that there's a relay in there. That's almost certainly what has failed.

What's inside your junction box?

(all your other troubleshooting sounds correct/logical to me)
posted by fake at 11:52 AM on August 26, 2010

I see from this ZX600f wiring diagram that the junction box contains a "starter relay". I suspect this is your failed part and that you can find one on eBay for a few bucks.
posted by fake at 11:58 AM on August 26, 2010

Yeah, the relay in the junction box sounds like a likely thing to check next. The wiring diagram shows it has a diode beside it (in series with its coil? can't tell, that's a poorly-made schematic) and diodes occasionally fail too. Replacing either the relay or the diode by itself should be possible and much cheaper than the whole box.

The other probable culprit is a corroded connector or corroded or broken wire. Hard to find, easy to replace.

What I'd do next is try to probe out how far the signal is getting, since you haven't found an individual failed component. Ground the - probe, and using the + probe, check the voltage at the input terminal of the start switch: it should be +12 (assuming the bike uses a 12v battery), and the output terminal should be at 0. Press the start switch and hopefully the voltage on its output terminal jumps to +12. Continue along the circuit, testing any points you can easily probe to make sure they respond to the start switch. Eventually you'll find something that doesn't, and you'll know the problem is between the last two things you checked. Narrow it down until you find it. Of course be careful in case poking some loose connection makes the start switch suddenly operational and the starter activates!
posted by hattifattener at 12:22 PM on August 26, 2010

I've seen A LOT of sidestand switches fail. Try jumping it. (All my dualsport motorcycles have their sidestand switches permanently disabled - they fail that often.)
posted by workerant at 1:48 PM on August 26, 2010

I agree with the above -- check the relay and the sidestand switch before starting to spend real money.
posted by Forktine at 4:05 PM on August 26, 2010

From my certified mechanic boyfriend:

Without getting my hands on it I would have to say check the voltage going into the relay, the part that activates it. Essentially it's a magnetic switch. If there is no voltage to activate it it wont close. Your service manual should give you a break down of the wiring to the relays. this will a least save you from buying a junction box that is not needed. Remember "chase the voltage" follow it from where it starts to where its going. Be sure to check connectors for any voltage drops. Anyway that's about the best advice I can give without getting my hands on it. I hope this is of some help to you.

From me:

Me-mail me if you want to know more and I'll get you two in touch. Hope this helps.
posted by vilandra at 10:30 PM on August 26, 2010

Response by poster: Wow, thanks for all the excellent suggestions, folks!

I forgot that the sidestand switch is already bypassed, so that leaves the relay and/or diode, or (deargodpleaseno) a broken/corroded wire. In either case, it looks like I have some circuit-testing to do. (Big thanks to hattifattener and vilandra's boyfriend for the specifics!)

I'll let you know how things go...
posted by fracas at 3:43 PM on August 30, 2010

How did things go?
posted by fake at 8:38 AM on September 21, 2010

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