[SOLVED!  See post 21]

Looking for any electrical guru insight.

I'm continuing my diagnosis started in this thread:

https://www.k100-forum.com/t12767-sudden-no-start-with-starter-button-where-to-check-next

But symptoms have changed a bit and was looking to maybe get some new eyes on the issue.

As it sits right now, my 85 K100RS will blow the #1 fuse every time I start it after it's sat after running.  Sometimes it will do it when I put the key on, then turn the choke on (fuse pops before engine starts).  Sometimes it will do it a few seconds after I put the key on without touching anything.  And sometimes it will let me start the engine, it will run for sometimes a few seconds, sometimes it will go about a block of riding before popping the #1 fuse.  Engine still runs and all, just functions tied to that fuse stop working (most importantly brake lights that keeps me from riding it anyway).

A month ago, it was doing this completely randomly (not just shortly after startup).  I pulled the tank and hooked a headlight bulb in line with the #1 fuse and jiggled wires until I found what I think was the clutch switch connector on the left tray under the tank would pop the fuse whenever I jiggled it.  I cut it out and wired it straight and it stopped blowing the fuse for a few days until the above current scenario.

Link to connector I eliminated that would pop the fuse when I tapped it: 

So why don't I just continue using the headlight bulb and find the short?  Here's the weird part - After it blows the fuse, I can replace that fuse and it will start and run normally - FOR AS LONG AS I RIDE IT... whether that be 5 minutes or an hour.  I've tried working every component while riding and nothing blows the fuse.  If I shut the bike off and let it sit for at least 10 minutes, it will blow the fuse on restart (in the above ways).  Then it works just fine after replacing the fuse.

The same goes for the Headlight bulb trick.  When I pull the tank and hook the headlight bulb up to the #1 fuse, it glows bright (indicating there is a short) for about 1 second, then it goes out (no short present), and stays out until I actually RIDE THE BIKE for a while, then let it sit again.

So strange!

Any thoughts?

I'm not sure what you know about this already, but I had trouble with fuse #1 blowing constantly and it turned out I had a broken wire from the temperature gauge causing a dead short when it rattled around and hit metal. Inge was very helpful, he described everything that is and isn't covered by fuse #1 so that may give you some starting points:

https://www.k100-forum.com/t11360-turn-the-key-and-almost-nothing-happens

Thanks for that insight.  I will have a look at that side of the frame tube (I was focusing on the left side because the choke, clutch and heated grips that are on #1 fuse are on that side).

I have a BEP 3.0 (simulates instrument cluster for a cafe project) and an Acewell 64566 instrument cluster.  I was always curious if the "TEMP" light would work.  I saw it flicker the other day while I was riding, but it was 100F outside and though I've never had any overheating issues, thought it was just really hot out.

Now that I've read the thread you linked me to, one of the minds greater than mine says the stock temp gauge uses the gauge and the temp sensor to output a reading.  I don't have the stock instrument cluster any more, so whatever signal the temp sensor wire going through the BEP is sending, shouldn't be right without an actual bimetallic spring inline (that used to be in the gauge in the cluster).

I'll definitely have a look at that wiring.

However, it just seems strange that no matter what I do after replacing the fuse, I can not get it to blow while riding it.  Vibrations/bumps/electrical load/etc, nothing blows the fuse except letting the bike cool down and attempting to re-start it again.

It's as if there is some kind of temporary resistance that needs to see a significant amperage then goes away.  I imagine something like corrosion between a power and ground pin in a connector somewhere that causes a short and blows the fuse *BUT* enough heat through that pin and it melts/eviscerates/cleans the pin so that it runs afterwards.  

I don't know.  I do know it's extraordinarily frustrating when the minute you put testing equipment up to it, the short goes away.  I guess I'm left with just unplugging everything one by one and taking a ride.  That's a real pain to re-assemble the bike after disconnecting every circuit

Disregard the bimetallic spring blather above.  I thought about it and that spring just moves the temp needle.  The signal wire should be enough to have a digital temp readout with the right resistance scale entered.  I'll still check out the temp wiring though.

I wonder if the oil pressure switch (in the oil pump ) is somehow connected to a positive wire ..
at turn on it would short out ...but after that and a few cranks of the motor  would remain open circuit for a good while until ...as you say cools down (loses pressure )

just an idea

Have you been using the heated grips on the low setting recently?

No heated grips installed on this bike.  Checked the connector under the tank... obviously just the female end is there - clean and unmolested.  When searching, that's the #1 suggestion for this situation so I tugged, prodded, pulled, etc on all that wiring and no short.

no you missed the point ...the oil pressure switch works by shorting to ground when there is no oil pressure ...its the way it works ...the instruments feed a 12v positive through a globe then  the to the switch - sensor ...so that It illuminates the globe when there is little or no oil pressure..  the globe is the current limit ..but if 12 volts was applied to the wire to the oil pressure switch directly  it would short out causing big currents and blow the fuse . just wondering if the wire that feeds the oil pressure wire  is plugged into the wrong place .

Oil pressure switch is not connected to fuse #1 (AFAIK)

Hi,

Yes, actually the oil pressure switch is connected to Fuse #1.

Fuse #1 feeds switched 12V to Pin 6 on the instrument cluster (among other things). The oil pressure indicator in the cluster is connected to pin 6 on one side of the globe (bulb in US terms), and to the oil pressure switch on the other side of the bulb. The other side of the switch is connected to ground. If there is an internal fault in the instrument cluster that shorts out across the oil pressure indicator in the cluster, what Charlie says will happen. If the oil pressure switch closes due to lack of pressure, there is no bulb to limit current and the fuse will pop.

Interesting.  So I'm using a BEP 3.0 which acts in place of the instrument cluster.

It has an output for Oil pressure warning described as such, "switches to ground when the oil pressure switch is activated"

The only time I ever saw the oil pressure or check engine light (BEP 3.0 has CEL come on for any of the warnings like coolant temp. oil pressure, etc - they're linked) was starting the bike in 40F weather and only briefly until pressure came up (and back then, it did not blow any fuses).

I'm skeptical of an oil pressure switch issue because it will blow the fuse sometimes with ignition on and engine off (no oil pressure - would make sense if it was the switch), and sometimes it will let the bike start, run and go a block or two before blowing the fuse...   if it were the oil pressure switch, it should blow it whenever I put the ignition on and it sees low oil pressure, right?

If I wanted to eliminate this from the possibilities, I would just unplug the oil pressure switch connector?  I'm sure I could find it myself, but I'm not near the bike, if one knows where it is offhand, please post.  [nevermind, I looked in the manual and it's under the tank on the right hand side around the radiator cap area, FWIW]

Charlie's assumption was that you had a bone stock bike with an OEM cluster.  You mention the BEP 3.0 (and if I had read the whole thread instead of the last post, I would have caught that ... Doh), which now means the OEM cluster is not present.  So, the problem can't be linked to your oil pressure switch.  It also eliminates any potential problem that might have existed within the OEM cluster as fed by Pin 6.  

So, concentrate on other circuits that are fed by Fuse #1.  You were given a list in the Motobrick forum.

Can you relate the timing of the fuse popping with applying either of the brakes, rear or front?

was just thinking the timing may have been consistent with the issue described

good to know

good luck with the fettling

I run my moto in 20ºF weather occasionally and its oil pressure hasn't stumbled like your bike's has. Appropriate weight oil and a high-quality filter with a functioning anti-drain–back valve should prevent that.

Anyway, have you checked the brake switch and its related wiring behind the right foot peg plate? They've been a source of mystery and headaches.

robmack wrote:
Can you relate the timing of the fuse popping with applying either of the brakes, rear or front?

Sadly no.  The only thing I was ever able to verify that popped the fuse was the clutch switch connector.  I've checked behind the right foot peg and the wiring is not pinched there, nor will applying any of the brakes cause the fuse to pop.

Having a list of what's powered by Fuse #1, I consistently work all of those functions when the bike is running after swapping fuses and nothing blows the fuse (except turning the bike off and re-starting later).

I have one other issue with the bike that I have yet to verify, but I don't believe it's related.  When the bike is started and running (and after getting above 2,000 rpm to excite the alternator) I only get 13.3V maximum output according to my BEP 3.0's battery voltage display.  Shouldn't I get 14.0-14.4?  I'm also not 100% sure of how the charging circuit should work - once the alternator is excited by going past 2,000 rpm, should it be putting out 13+ volts even at idle?  Mine consistently goes down to 11.9 or so at 1000rpm, and slowly ramps up from 11.9 to 13.3 once it gets above 2,000rpm.

Adam,   I thought I'd go back through your threads to read the whole story.  Here are some bits that makes me nervous:

The hard part is I bought the bike without an instrument cluster.  I'm not sure if the previous owner just cut the wiring/connector out (I assume it was supposed to run up above the triple tree where the cluster is - it's obviously not there now.  I know from looking at the BEP 3.0 instructions that there should be two 12 pin single row connectors for the stock cluster.

As I got it:

Anyway, I'm happy - it was very easy except finding room under the tank for the wires.  Everything worked last night and this morning I have a check engine light and oil pressure light on the Acewell.  I know for a fact the Check engine light wire is not hooked to anything at all - I believe a wire or two is getting smashed.  I couldn't make room under the crossbar of the frame that the upright bar going under the gas tank tees into.  The wires lay flat over this bar and I think the gas tank is smashing them.  I'll update the thread when I've got it figured out.

At this point I still suspect a bad clutch switch at the trans.  When I was short-testing originally, I would occasionally see a wisp of smoke come up in the area between the tank and the seat from below ....   the clutch switch is down there, but so is the gear indicator switch and side stand.  I could actively make the fuse pop by wiggling the clutch switch connector under the tank so I eliminated that, but perhaps the switch itself is shorting and melted the connector first?

So, you got a bike with a chequered past, a missing gauge, unknown wiring mods by the P.O., you see smashed wiring and you see smoke from the wiring harness when diagnosing your fuse problem.

I get nervous when I read about severed wires, crushed insulation and electrical things letting out their magic smoke.  I would be highly suspicious of the state of your harness at this point.  It might be a good idea to keep an eye out for a suitable replacement on The Bay.

Thank you for the suggestion, that may be the route I end up taking.

For now, I haven't given up on finding my short.

A few clarifications from the posts you quoted above.

1) I stated that "I know for a fact that..."  when in fact, I was quite wrong.  The Acewell 6456 uses the check engine light as a "catch all" for any of the available warnings (oil pressure, coolant temperature, etc) and whenever one light comes on, the other should come on with it, so it was working properly in that regard I believe.  Was there really an oil pressure issue?  I can't be certain - the bike ran great and still runs great without any symptoms of oil pressure that I can discern.  I only saw that light once and never since.

2) I found the 2 connectors for the cluster under the tank and they are currently plugged into the BEP (I'm not sure I updated that old post, it was shortly after posting I found them).

3) The only "crushed" wires under the tank are the wires that go from the BEP which I put in the relay box, to the Acewell 6456, and possibly the two wiring bundles that went to the original cluster connectors.

4) The smoke is still a mystery.  When the short was persistent, I could duplicate the smoke whenever I wanted by inserting a 20amp fuse into #1 for a few seconds then pulling it out before it popped.  When I used my headlamp bulb tester, I'm guessing the bulb absorbs a lot of the electricity because I do not get any smoke as long as I have the bulb plugged in to fuse 1 (when the clutch switch connector was a permanent short, I could have the bulb tester plugged in for five minutes lighting up the bulb and no smoke...).  Since eliminating the clutch switch connector, I have not been able to recreate the short for more than a second or two (bulb lights up, then goes out and short is gone until bike is ridden and then sits).


Now after looking at the above, I'm wondering if there is a short/cracked wire in the instrument cluster harness that might be pinched under the tank - Pin 6 is the one for Fuse #1 that has oil pressure connected to it, right?  That'd be an easy first place to look.  I'm nearly certain the smoke came from directly below that point though.  The only thing on Fuse 1 below the relay box is the TGPI, right?  Am I right in thinking the clutch switch is on the handlebar and not in the belhousing?

The clutch switch is on the handlebar, you will see the electrical cable near the clutch lever, it goes into the loom under the gas tank.

You need to pull out the cable from under the tank to unscrew it, putting it back you screw the end into the handlebar housing before you route the cable under the tank.

On a 2v engine the rear brake switch is the same part so you can take that and use it as a test/replacement and put the tank back. rear brake switch can be replaced without removing the tank.

I think I'm going to remove the clutch switch all together.  Was examining the M-Unit wiring diagram someone made but it didn't have a the clutch switch on it.  It obviously terminates at the clutch lever on the handlebar, and at the connector under the tank.  From the connector back to the fuse how is it ran?  Into that big bundle of green wires?  What about the other wire on the connector?

Also, I'm guessing it's the choke cable, but I was following a wire that ran down the left hand of the under tank tray, then went down behind the fuel rail but right near the ignition coils and then it was too tight to follow and I couldn't see it.  Felt like a cable connector.  Am I right in thinking this is the choke?

UPDATE!!

This is going to be anti-climactic but something has changed!

I went to ride the bike to work this morning.  I was going to do my normal routine of blowing the first fuse, swapping in a new one and taking off but before I did that I had an idea - instead of buying fuses over and over, I can just plug my headlight test bulb into the fuse location, let it glow bright (short present) and then turn off (short gone) a second later and then I can plug the good fuse back in and ride away - figured this would save me 2 fuses a day until I get this thing sorted out.

Well I put the bulb tester in place of the fuse, turn the ignition on and watch the Acewell go through it's sweep half way, then the RPM needle drops to zero and the digital screen goes dark (except the clock - this is what normally happens after blowing a fuse)  *EXCEPT* the oil pressure light is glowing by itself and the tester bulb has not gone dark, it's glowing bright.

I pull it out and put a fuse in and try again, and it pops.  I then put a second fuse in (for the last week, this is when things would run normally) and it pops!  I put the tester bulb back in and it glows bright and this time the check engine, oil pressure, temp, and fuel lights are lit up on the Acewell.  I can press the start button and the fuel pump goes and you can hear the faintest whisp of the start engaging but it won't turn (tester bulb still glowing bright indicating there is an active short).

I flip the controls on and off a few times and lights slowly disappear until I'm left with the oil pressure light that never turned off.  THEN...   I give up because I have to go to work - but am excited that I'll be able to do some real diagnosis tomorrow - EXCEPT... I go to turn the bike off and the Acewell won't turn off!   Kill switch off, ingition cylinder off, Acewell still has power.  I disconnected the negative battery cable and it turned off - I re-connected the negative terminal and it did not power back on.

I think I know where to look for my short now - it's gotta be somewhere in the original instrument cluster's two short harnesses (or I suppose in the BEP itself).  All of these wires are going over the rear cross bar in the frame and the gas tank is laying on them, so I'll start there.

I've never wanted to leave work so bad.

SOLVED!!

What a waste of time.  The symptoms above made me think it had to be somewhere in the wiring to the BEP (stock instrument cluster wiring).  I unwrapped all the wiring harness on that side of the tank and checked for shorts.

I'm amazed at what good shape the actual wiring insulation is in.  It's soft and pliable, flexes without cracking - feels like new.  This bike supposedly only has 20k miles on it.  NO SHORTS FOUND in any of the wiring harnesses.  The black tape/rubber sheathes the wires were in were trashed.  I re-wrapped them with standard electrical tape for now.  When I relocate all my electronics into the air box I'll use proper tape.

After not finding any shorts I ended up tracing by hand every wire that was under the tank and unplugging their connections.  I got to the clutch switch wire (whose connector was the original problem that I removed and hardwired).  I followed it down to the location it terminates ahead of the coils, behind the rear end of the fuel rail and the end was hot to the touch!

I figured there must be a short internally into whatever that is there... I'm still confused if that's the clutch switch or something else. I thought the clutch switch was on the hand control, and ended up in the relay box or something.  Anyway, I cut the wires where I had removed the connector under the tank and VOILA!  No more short.  I tested to see if the bike would crank and sure enough it did (bike in netural, clutch lever left alone).

The connector was working as a fuse itself apparently. When I removed it, the end at the trans was getting super hot.  I'm not sure why it would blow a fuse at first, then not blow the second fuse and ride all last week.  

I took it out for a ride and made several stops shutting the bike down for 10-15 minutes each (it would previously blow the fuse on re-start after this), and no more blown fuses - everything works as it should.  In fact, my fuel gauge was acting flaky before this and now it's stable.

If I can make one suggestion to everyone looking for shorted wires - make a headlight bulb tester like the one below.  It's super easy and made the job so much easier (light bulb on - short present, light bulb off, no short present):



Thanks to everyone who made suggestions - it always helps to get the brain moving.  I'm excited to finish the project now - I still have to relocate the battery, MAF, and ECU to clear out the underside of the seat area for my custom expansion tank.  Was waiting to figure this short out before I start moving things.

Love my K again!!