HOT main fuse and subsequently red connector,

[john.hand]

Hi all,
I've been helping my neighbor work on his 79 CBX the last few weeks. He's an older gentleman, member of the CBX club from the 80s to early 2000s, but currently in poor health and with limited income. The bike is gorgeous and has been sitting in his shed, covered, but unridden for years. He would like to sell it so I told him I'd help him get it ready. It wouldn't start, but we rebuilt the carbs and it started like a champ....sounded so good. I noticed some smoke from the right side of bike and shut it down. The red/red white wires from the main fuse were melting. Connector melted as well. Due to amount of damage, I think this wire and connector were melted before we started after carb rebuild. I replaced the wires and the fuse assembly and gave it a test.
At this point, it will get hot with ignition on and kill switch on. Alternator and R/RR unplugged. Bike not running. With coils connected and headlight connected, fuse noticeably get hot. If either the coils or the headlight is disconnected, the fuse will get warm, but not hot. Over time, the red wires near red connector will begin to heat up as well. I have yet to let it heat up the point of melting insulation again.

What I've done:
-replaced Main fuse assemply and spliced a good red connector from an old harness he had into the bike harness(he has a great deal of parts, many in new OEM bags and boxes)
-Cleaned all spade and female connectors on harness, plus contact cleaner
-unplugged R/RR and Alternator out of circuit
-verified coils(Dynos) ohm'd out right
-Jumped coils strait from fuse, bypassing wiring trunk
-Checked ground near starter
-reran ground from coils mounting block
-tried old stock coils (actually got hotter, quicker)
-tried an old kill switch
-tried a different R/RR(before I noticed it will heat even if not connected)
-checked voltage drop from fuse to coils(I spent a lot of time looking in that area since it seemed to heat up most when connected)....just a few mV drop

I plan to use my other VM that can do DC current and see if I can see what kind of draws I'm getting from various components.

Anyway, I'm kind at wits end. I know theory and troubleshoot pretty well, but this gremlin is really kicking my tail. At least I've gotten quite good with the CBX schematic.

Any other tips or things I should look at/consider from your CBX experienced types? One post I saw that was nearly identical ended up being a corroded alternator plug. Definitely not the case here.

Appreciate the help,

John

[john.hand]

The bike with the gremlins.

[letxbruce]

Seems like you are close on the trail. Sounds like the main power feed circuit downstream from the fuse has very high resistance causing an increased current draw on the fuse when powering up the lights and or coils. I found that my main power feed (I think Red wire) was totally corroded inside the insulation with no outward sign of a problem. This caused a lot of heat . One other thing, while installing Dyna Coils I managed to route the hot wire terminal so it pointed up to the bottom of the fuel tank and eventually wore the insulation down so it intermitently shorted against the bottom of the tank.

Bruce

[daves79x]

Take the ignition switch apart and clean the contacts there. The 30 amp fuse WILL get warm, but should not get hot enough to melt wires. What you discovered initially had happened long ago, I'm sure. Connect an ammeter past the 30 amp fuse and see what the draw is and compare it to what is connected.

Don't worry about the smoke right now - sitting for a long time will do that initially.

Dave

[john.hand]

Thanks Dave. I actually pulled ignition switch apart the other day, those three tabs are a pain....also hang tested another. He seems to have two of everything.

I will update when I solve this beast.

John

[daves79x]

There's a trick to the switch. Key needs to be turned to a certain position to release tabs without breaking one.

[Larry Zimmer]

I would think that if things are becoming that hot, something is drawing a large current -- as in, there is a short somewhere. A high resistance won't draw much any current. It's a low resistance(where it should be high like a coil with an internal short) or a short (like a wire chaffed through its insulation) that draws high current. Either that, OR, a high current, such as charging current, that is trying to go through a high resistance connection that should be low resistance.

[john.hand]

I would think so too Larry, I took my DC ampmeter over today and with everything connected and on(but not running), bike draws about 15amps. I have yet to find any hard shorts, or soft ones for that matter. Coils were about 5A alone. Worst thing I can find, is a 1.5 volt voltage drop on the wire from brown connector to dyna coils. I put a test cable together to run the coils straight from main fuse rather than letting all the current run through the main harness. That cooled things down a lot, and the voltage drop reduced to .3 or so. For this reason, I suggested he let me install the relay mod for his coils. Just seems to be a tired harness.

Dave, where were you when I was trying to take the ignition switch apart?!

John

[Jeff Bennetts]

John a fellow here on the forum sells new wiring harnesses, it might be the simplest if not the best solution.

His name is Falldownphil, do a search using "new wiring harness" and Phill's name, good luck getting your buddy going it looks like a beautiful CBX.

[john.hand]

Thanks for lead Jeff(no pun intended). Friend is on a limited income, so trying to do as much pro bono as I can. Mod will run about 30 bucks which is even tough for him. I am fronting that. I will look into harness and run by him. Suspect he wont be able to move forward with that.

[Larry Zimmer]

Without taking time to consult wiring diagrams, could there be something/somewhere in the charging circuit with a short or other malfunction that is putting a large current through the alternator? (Dave, perhaps you know something here right off the top.) [Shorted field coil(s). Regulator malfunction. Diode failure? Or?] 15 amps is near a dead short!!

I think the 1.5v drop to the coils when run through the full wiring harness, including switches, is to be expected when connections, etc haven't been disturbed/cleaned for 30 years. Nothing wrong with doing the relay thing. Just time and a little $ that won't resolve the primary problem.

Any thoughts on the charging circuit, Dave? Beyond that, just continue isolating all the various circuits and testing individually. It will eventually show. Just a lengthy PIA thing to do.

[daves79x]

The way I read John's description, he had the alternator plug unplugged. Now this does not take the regulator out of the loop, however. I'd be unplugging that as well. Oops, see that the rr is also unplugged.

Dave

[john.hand]

~15 amps was total system current. So half main fuse rating of 30A which seemed reasonable to me, but that could be my lack of experience with the bike. Headlight alone was about 3 for example. And doing a little calculation based on its wattage and the voltage, the current was accurate.

If it would prove helpful, I can capture each systems current flow(basically metering while each fuse is individually installed) which may highlight an anomaly that I don't notice in a system. Had to be careful, since my meter has a 10A rating for current checking, so I had to check each branch separately then add them together for total draw.

Anyway, I appreciate the input on this.

John

[Jeff Bennetts]

Just something worth mentioning John, even though you said you cleaned the connector spades, did you look close to where the wires terminate/crimp into each individual spade, male and female, sometimes it's necessary to trim the wire back an inch or so to eliminate the corrosion that can migrate up the strands of the wire end.

[NobleHops]

There's a trick to the switch. Key needs to be turned to a certain position to release tabs without breaking one.

Just did get reminded of this. Turn your key all the way to "Park" and that locates a recess in the right position for the fangs to press into.