Hello I have owned my 88 k100rs since 2006. It's been a great bike. Here lately it's been rather moody and unreliable. The fuel pump intermittently stops working. I've replaced The fuel pump and filter. It checked the fuel tank connection, changed the fuel pump relay, kill switch, swapped a used but good FI computer and I haven't had any results. This is why I'm here.

While you were replacing/swapping parts did you clean all the contacts? I've done all of mine with abrasive and deoxit and will likely do them all again with the addition of dielectric grease.  If it isn't components and contacts then it might be an intermittent short in one of the wires.  The problem with intermittent is they can only be identified when they aren't working.  Since the problem shows itself with the fuel pump you might want to begin testing from there back.

It might be either the ground or 12V wiring that passes through the fuel level sender.

You can take the gas cap off and jump power directly to the fuel pump.  The smaller diameter fuel pump terminal is 12V and the larger is ground.

For obvious reasons be very careful not to generate any sparks in the gas tank when doing this.

POORBOY88 wrote: The fuel pump intermittently stops working. [I] checked the fuel tank connection . . .

Does it stop momentarily then restart or does it stop altogether and there is no telling when it will restart?
Did you check for continuity both the outside 4-pin connection wiring and the two wires from the fuel level sender to the pump that duck has described?

The bike just dies randomly. No telling when it will start again. Currently I've just been playing swaptronics. Ive sprayed contact cleaner on every connection I've touched. Haven't done the dielectric grease though. I know it's sort of hillbilly I was thinking about just hooking up the tank wiring to a toggle switch. Anybody know if that would effect any of the other parts of the fuel system if I did that? Excess fuel should just go back to tank right?

Also I haven't checked the wiring as duck described but I will hopefully tonight when I get off work.

Several years ago I had a K100 guy come by my house.  His fuel pump wiring went under the gas cap.

Jumping the fuel pump with a toggle switch will work.  I'd recommend having a fuse in the circuit though. It won't impact anything else.

Another option would be to jump the fuel pump to the fuel tank connector so you're just bypassing the fuel level sender.

The green/white wire is fuel pump 12V. Brown is ground.

The four pin connector under the tank is a known source of problems. The problems can be intermittent in nature and even the application of the two part DeoxIT can fail to solve the problem. When it runs try wriggling the connector, if it stops replace the four pin connector. My connector started to have intermittent problems after behaving itself for 25 years. Cleaning helped but when it failed outside an electronics supply shop, I took it as a sign and replaced it with a waterproof connector. No problems since and cheap insurance for around $20.00 Au.
A smear of silicone grease around the seals makes it doubly sure to be waterproof.
Regards Martin.

Another option is to use an SAE trailer wire connector.  The colors even match up!

I replaced the four pin connector with a trailer light plug as duck suggested. I'm not saying it's fixed yet but the bike hasn't missed a beat. Also put in a rocker switch for the fuel pump just in case. After I put some more miles on I will let you all know. Thanks for the help.

Nice thinking - the update.

Just solidifies the received wisdom that the 4-pin is the place to start looking with these symptoms.

Thanks.

The pesky plug that so often gives trouble (happened to me also). Over time there has been considerable discussion about repairing/replacing the plug. I will wander down to the workshop and look at some TIG welder connection plugs I purchased some time ago. The plugs come in a variety of shapes, sizes and number of pins. There is a 5 pin 1/2" connector plug that is very solidly made and small in size. This may be a good compact alternative to the 5 pin SAE trailer plug (which I think is physically larger than the original plug).
In terms of internal to external fuel tank wiring I have thought of replacing the internal wires with new PFTE coated high grade wire going from inside the tank and through the round base of the fuel tank to the external plug. This would require removal of the hard sealing compound the wires are cemented into at the base of the tank and replacement with a suitable hard sealant after rewiring. Does anyone know if there is a long-term leakproof sealing compound to do this. Would a fibreglass epoxy be suitable or is there a better product?
Later: Back from the workshop. I think this type of connector plug is a goer. I purchased several different 7 pin plugs. 1 plug for the female plastic moulding is 12.6mm diameter, the other is 15.45mm diameter. The male part of each of these 7 pin plugs has robust metal male pins and each male/female plug section is set in metal with screw together - an advantage in keeping things together as opposed to just a push fit. My original plug has worn over the 36 years it has been in place so is a bit sloppy and after dioxit cleaning and re-widening the male pins, I have never been happy with it. I intend doing an in-tank rewire at the s above and fitting new plugs. Ebay USA has the TIG welding plugs from a supplier offering various numbers of pins including 5

I've previously tried a similar thing - sealing the wires from a petrol level sender where they pass through the mounting flange (not the K bike).
I found that a product called JB Weld is good versus petrol. But I did have issues with the way it seems to expand on curing - it was rupturing the plastic housings.

Thanks Chris846 - I have some JB Weld