I picked up an 1986 k100rt cheap a month or two ago. It had been parked up a while because, supposedly, the fuel pump was stuffed. I've just started trying to sort it out.

What I have found is that the fuel pump doesn't work because there is no power getting to it (green/yellow wire on the connector that goes to the tank). I've traced it back to the fuse (2nd from bottom) and from there back to the fuel relay. The fuel relay switches when I take it off and test it, but doesn't switch when connected into the circuit. So from there it looks like the problem is in the circuitry that triggers the fuel relay. There are 5 wires - a large red one from the battery - this is live like it should be, two green/red, one that go to the fuse box, and one elsewhere, and a brown/yellow that go to the ignition unit, and another one (cant remember the colour). What I think I need to know is how the brown/yellow wire is controlled through the ignition unit, as in if the ignition unit is stuffed, will this also disable the brown/yellow wire.

Of course, if I've totally got it wrong, feel free to offer advise/scorn/criticism..

The ignition ECU grounds the fuel pump relay coil (yellow/brown wire), when a signal from the hall sensors is received.........or a signal from the starter button.

might be worthwhile checking the earth points as well

did you make the measurement from the frame to the positive wire to the tank ? or the cable which supplys earth on that same connector ?

I recon a good cleanup of the main earth cable at the battery and at the frame is always a positive start at rectifying anything electrical.

we have seen some bad relays of late ...so just a heads up

Here's a bit help;
http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/electrical/diagrams/fuel-pump.htm

More fails, more wires
http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/electrical/diagrams/interactive_diagrams.htm

Inge K. wrote:The ignition ECU grounds the fuel pump relay coil (yellow/brown wire), when a signal from the hall sensors is received.........or a signal from the starter button.

Ok, I can check if it does that on the starter button. I'll also check the other side of the fuel injection relay (green/yellow on the diagrams wheeldigger posted links for). It should have power from the second fuse down from the top. I'll check the earths too. All the instuments light up, blinkers work and the starter motor works, but no headlight or oil warning light. I did check the fuel relay was actually connecting through when tripped so I think its ok.
Thanks all
Phil

charlie99 wrote:might be worthwhile checking the earth points as well

did you make the measurement from the frame to the positive wire to the tank ? or the cable which supplys earth on that same connector ?

I recon a good cleanup of the main earth cable at the battery and at the frame is always a positive start at rectifying anything electrical.

we have seen some bad relays of late ...so just a heads up

G'day Charlie
I checked from the positive wire to the frame and also directly back to the -ve on the battery. Cleaning earth connections is always a good thing.
cheers, Phil

um doesn't the pump get power from the second bottom fuse ?

worth checking
I have seen them blow ....just from being ..semi seized ..or without use for a long while

check them all

charlie99 wrote:um doesn't the pump get power from the second bottom fuse ?

worth checking
I have seen them blow ....just from being ..semi seized ..or without use for a long while

check them all

Yup, but that power comes from the battery via the fuel injection relay, which is switched on by the green/yellow and brown/yellow, and the brown/yellow is earthed by the starter switch or ignition unit, and the green/yellow gets its power from the 2nd fuse down....  Goes round and round in circles  

Phil measure the fuse with a meter I have seen many of those blade type go O/C and not show as blown.

Don't know what happened to my post, so I'll try again

I have success.. heres the steps

I connected a temporary jumper from the brown yellow wire at the fuel relay to earth. The relay switched when the ignition was on and I have power to the fuel pump +ve wire at the tank.
Then I pulled the spark plugs and turned the motor over. Good spark at the plugs suggesting the Hall effect sensor and ignition control unit were ok.
Next thing was to remove the connector from the back of the ignition control unit and check the brown/yellow wire was connected through to the fuel relay. All good there.
So, hoping that to was just a bad connection I put the connector back on the ignition unit and removed the temporary jumper connection. Success - relay now switches when I press the starter button and power gets through to the fuel pump wire. Voltage is a little low at 11.5v, but the battery is down a bit too.

Tomorrow I'll clean up all the connections involved and put the tank off my other K100 on this one and see if it goes 

so a brumby socket on the relay carrier phil ?

or the ecu pinout ?

good find

I just did my solenoids on the door locks of the rolla today
would activate sometimes
also female spade connectors of the plug, male spades on the solenoid socket

I used fingernail sanding boards ...(cheep as from the discount shops ) cut a little to size, to get into the spade females and get the crud off ...likewise with the solenoid side
some cleaner then the deoxit gold to condition the connectors
nice strong pull now

charlie99 wrote:so a brumby socket on the relay carrier phil ?

or the ecu pinout ?

good find

I just did my solenoids on the door locks of the rolla today
would activate sometimes
also female spade connectors of the plug, male spades on the solenoid socket

I used fingernail sanding boards ...(cheep as from the discount shops ) cut a little to size, to get into the spade females and get the crud off ...likewise with the solenoid side
some cleaner then the deoxit gold to condition the connectors
nice strong pull now

ECU pinout. The connections actually look quite clean. Must have had a thin coating of crud. Evidence the bike has been near the seaside so it looks like I should unplug, clean and remake all connections. Obvious really.

No go with getting it to run. Strange happenings with the electrics. Power at connector near the tank has gone, except occasionally. Then I get an odd effect when I check it with a multimeter. With everything off the meter holds at -12.6 volts (not +12.6!) and lowers gradually to zero. Some sort of induction effect? Dunno. Anyway, no more time to play with this so I'll park it up for a while. And I though old jap electrics were a pain.

Could it be a dodgy relay ?
the points inside may have welded together at sometime
and now can't hold together /allow enough power thru 
hope its something as simple

cheers Tony

Toto_jp wrote:Could it be a dodgy relay ?
the points inside may have welded together at sometime
and now can't hold together /allow enough power thru 
hope its something as simple

cheers Tony

Could be something simple and probably is. Dodgy relay, dirty connection etc. I've just about resolved to pull all the electrics apart, clean all connections and check everything. The plan is to semi restore this bike anyway, so I might as well do it properly rather than trying to cut corners.
cheers, Phil

Check the pesky crappy ignition switch and kill switch...  These can cause big problems by making intermittent connections due to arcing and corrosion.... causing all sorts of intermittent operations...

Here is how to clean it...

I've used Don Eilenberger's post which is excellent with pictures etc....

<http://www.eilenberger.net/K75S/IgnitionSwitch/>

Also, years ago, on my 1985 K100, the fuse that powered the fule pump (and other items I believe) was blowing intermittently...   found the power wire inside the fuel tank was chaffed thru to at the tank vent aluminum line inside the tank...  I repaired it and covered with alcohol resistant sleeve, and tie wrapped it to a stand off from the line...

This doesn't sound like your problem as the fuse blown is the smoking gun!!

Thanks guys.
The thread may be old however the info is still good.

Update:-
In my case a bad side stand switch.

The lesson - its not enough to check to connector block but to check the operation of the switch as well before looking for a deeper problem.

For the K11 guys some easy reference.