Honda CX 500 Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
Stock CX500 C with hot battery is dead in the garage.

Turned key and the cockpit was dark - no head, gauge, oil or neutral lights, so started down the usual trouble path. Battery pushing about 12.5 volts at terminals. Solenoid hot, starter turns normal when I cross the terminals with screwdriver. Main fuse is intact, blade type wired years ago, removed fuse and tested across gap, all good. Voltage coming into the ignition switch is about 12. Disassembled switch, was good inside, cleaned, reassembled. The next obvious place to check is the fuse panel which is all reading zero. No burnt fuses anywhere, so went backwards to the red connectors between the forks, and get varying voltage there. Sometimes 12, sometimes just 1 or 2. Seems like the switch is not to blame, but would love to somehow be proven wrong. Doesn't seem the thing to suddenly fail sitting in the shed for two months.

Do I really have to burrow under tape into the wiring harness now? Hate to say 'ran when parked,' but it was really going well after the triple bypass 500 miles ago. What can happen during a few weeks in the garage? What am I missing? I dis/reconnected all obvious points, cleaned ground posts on frame and inner headlight nacelle, checked connections on fuse panel, those are clean and shiny. again, all ignition terminal blades look great, wires intact, etc.

so: where do I look next? How do I fully eliminate the possibility of the great looking ignition switch being at fault? Where is the next point of failure between the switch and the fork harness/ fuse panel? Should I begin untaping the harness to inspect individual wires?


Other notes-
As it turns over via solenoid and I pull the plug boot, it is sparking blue, so that should mean a healthy ground through the kill switch.

Oil light failed before it sat, but the bulb is good. Did not replace the switch itself or check continuity along the way. Probably unrelated, but when nothing works, everything is suspect.

again, no burned fuses, but testing from + battery terminal to fuse holder, it grounds out (?) to produce 12v meter reading, exactly like grounding to frame.

I have the FSM wiring diagram and read it all ok but often need hints at the logic of tests at different points and real likelihood of failure

The bike always starts in the rain, even when sat outside, but can sometimes bog in deeper puddles or heavy downpours - almost never dies, just struggles a bit a those times and seems to feel like an ignition problem. I have always assumed this is more about the old ass brittle coils with micro cracks and need for new wires/boots/etc and that's all on the long list of things to replace. Again, probably unrelated.


What now?

thanks
LP
 

·
Registered
Joined
·
426 Posts
Pteromoto I would try looking at ignition switch or wire loom from switch, and go from there also check the wiki . Am sure others will comment soon. :) I hope this was helpful. Btw when this happened to my bike it was ignition switch that had fused it self internally . Cxphreak has a link for electrical switches in his signature line. You might also add your bike year and model for other people more knowledgeable than myself to help you :)
 

·
Registered
Joined
·
882 Posts
When you say the solenoid is hot, does that mean hot to the touch, like temperature-wise? If so, I would unplug the solenoid and measure the resistance of the coil. It might be fully or partially shorted out.
 

·
Registered
Joined
·
1,149 Posts
I would suspect a broken wire that sometimes makes a bit of contact when you turn the steering head. You'll have to unwrap the harness where it bends the most and try to isolate the wire with the break inside the insulation. It may LOOK okay, but chances are..
 

·
Registered
Joined
·
30 Posts
It seems that the grounds could also be the culprit, because they are just as common as the power wires. Have you tried grounding directly to the frame or engine from any of the lights?
 

·
Super Moderator
Joined
·
14,775 Posts
How did you check the fuses? You can never tell for sure just by looking because after years of normal vibration (everything vibrates as you go down the road) the link inside the fuse can break right next to where it is welded to the cap. When that happens the fuse looks perfect but does not conduct. The only way to tell for sure is to take each fuse out and check it with an ohm meter (should read zero ohms).

It could be the ignition keyswitch too. Try working it back & forth a few times and jiggling it while watching the instrument lights to see if they come on at any point.

Did you say you looked inside the headlight? If it sat for a few weeks this time of year something may have built a nest in there or tried to store food for winter or something and disturbed (or even chewed through) a wire.
 

·
Registered
Joined
·
3,771 Posts
I had an occasion last summer where someone was being mentored in my garage where someone had a broken plastic plug between the wiring harness and the switch plug. Pull the plug and make sure that there is no broken plastic on either the harness side or the switch side and that all of the plugs and pins in the plastic are properly seated.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #9
thanks for the responses guys - will post some pictures of the switch soon.

Joebuck - it's an 82 CX500C stock with about 40K

Missing linkage - by hot I just mean it turns the starter when crossed and I get full 12 volts on either side of of the solenoid while it's disengaged and onward through the main fuse, so I think that's fine.

MCreviver - that's what I'm afraid of.

70smechanic - good idea

Sidecar Bob - yeah, had the headlight nacelle apart when I checked the ignition switch and have done more frustrated jiggling than I want to admit. Also the seat and tank off to see the whole loom and can find no evidence of rat chewage. I was almost hoping for it by then. Also would test fuses individually or try jump wire, but there is no current at the fuse clips themselves.

Davidfromwisconsin - I hoped for that too but all connectors look great - unbroken and shiny

thackney - Mouse Trap Systems
 

·
Registered
Joined
·
16 Posts
Discussion Starter #10
Also to be clear none of the day of fiddling so far has lit the gauge cluster at all or sent any current to the fuse panel - no headstock wiggling or disassembly or reconnecting or anything has seemed to make a difference
 

·
Registered
Joined
·
16 Posts
Discussion Starter #11
Getting 12.26 volts coming into the switch. Good continuity measurements for switch with key in on position. on the bench between paddles for primary 12v red wire going in and black wire going out and black/green wire going to auxiliary. When the switch is installed and off, red wire is still solid 12.2. Then when key turns on, voltage drops to zero from that lead. What the hell? Even if switch was faulty, how could it kill current measurement from 12v wire from solenoid? Switch is clean, tight and looks great- pics below. Also, when I try a jump wire to connect red and black in the clip, nothin happens.
 

·
Registered
Joined
·
3,999 Posts
When the switch is installed and off, red wire is still solid 12.2. Then when key turns on, voltage drops to zero from that lead. What the hell? Even if switch was faulty, how could it kill current measurement from 12v wire from solenoid?
You probably have a break or bad connection in the power wire, you are getting 12 volts,,but no amps. When you try turning on the lights, etc. the wire is not carrying enough power to do anything.
 

·
Super Moderator
Joined
·
21,155 Posts
I had this with a bike I was working on recently. It had an overheated and broken main red in the loom. I traced it back to behind the engine hanger and at this point cut both ends and added a new one from fuse to ignition switch..

As pointed out above, physically check the main fuse too. Old ones can do funny things.

On this one the main fuse had been bypassed, - a very bad idea.
 

·
Super Moderator
Joined
·
14,775 Posts
OK, time to stop using the scattergun approach and go at this logically.

Lets start with the obvious & simple: Are you sure the battery is fully charged? You can't really tell just by measuring the voltage, you know. BTW: 12V is nominal, not actual - your battery should have 12.6V when fully charged and with no load. Connect your voltmeter across the battery and see what happens when you turn the key on. It should decrease a bit, like maybe from 12.6 to 11 or 12, depending on what is drawing current, but not by much more than that. If turning the key on causes a substantial decrease in the voltage, charge it for 14 hours at 1A and try again.

You said you replaced the main fuse with a blade type and it looks OK so it probably isn't your problem but if you check it we will know for sure. Looks can be deceiving. Measure the voltage relative to ground on both sides of the fuse to make sure it is working. You should have the same voltage (whatever your loaded system voltage is - usually between 12 and 12.6) on both sides. Just for good measure, unplug the fuse and measure at both ends of its socket (should be full voltage at one end and zero at the other with the fuse removed).

If that checks out OK its time to look at the grounds. The ground circuit on these bikes has a major design flaw: The wiring harness ground does not connect directly to the battery negative. The battery negative is connected to the starter motor bracket, which is bolted to the engine's rear cover. The frame is connected to the motor through the motor mounts. Most of us think that the harness grounds to the frame under the seat and in theory it does, but the bolt that attaches the ring lug actually screws into the airbox bracket. This means that anything connected to the harness is connected to battery negative through the connection under the seat, the frame, the motor mounts, the bolts that fasten the rear cover, the bolts that fasten the starter motor bracket and the starter motor bracket.

A few years ago I spent a lot of time chasing electrical gremlins before I realized that. With all of those places for something to go wrong its no wonder I was getting strange voltages where there shouldn't have been any. I removed the ground connection under the seat, extended the green wire and connected it directly to the battery's negative terminal. Those gremlins went away instantly and never came back. IMHO, this is how it should have been done in the first place.

To find out if your problem is ground related, start off by turning the key on and measuring the voltage between the negative terminal of the battery and any green wire in the harness. You should get zero volts. If you read anything more than maybe 0.2V when the headlight is on and the engine off your problem is in the ground circuit.

Even if your problem isn't in the ground circuit the mod I described won't hurt to do later on after you have figured out what the problem actually is.


If none of those exposes the problem you will need to start tracing through the schematic and measuring voltages until you find where there is no voltage when there should be. Let us know your results and we can help you figure out what to measure next.
 
1 - 14 of 14 Posts
Top