How do the oil and coolant temp switches work?

[sooprvylyn]

I'm talking about the switches connected to the oil/water pump. Am I correct in assuming these are just ground switches triggered by oil and coolant temps? Can these just be connected to the negative terminal on a 12v led light and give me proper function?

[frankenduck]

Oil switch is binary. It grounds when pressure is low. Yes, you could probably LED it.

The temp sensor in the water pump has lower resistance as the temp increases. It only connects to the temp gauge. It has no impact on fueling or the temp indicator in the cluster. Those functions are driven by the temp sensor in the coolant output pipe at the top front of the cylinder head.

[sooprvylyn]

Thanks

I assume the upper water temp switch is not binary either? Basically the signal must go thru the ecu and the ecu sends a signal to the coolant light?

As I understand it, the coolant fill cap will blow before any engine damage? So maybe a coolant light isn't strictly necessary? 

Easy enough to do the oil light at least.

[frankenduck]

Yes, the rad cap will blow before any engine damage. (248 F)

BUT, once the rad cap blows you need to let the bike cool and refill the cooling system. Having a temp indicator (lights at 239 F on a K1100) lets you shut down the engine to let it cool before the cap blows. (I once did a long summer ride on a 93 K1100 with a bad fan and the temp light helped me keep the rad cap from blowing when I'd get stuck in slow traffic at 90+ F.)

On a K1100 you can wire up a temp warning LED with 12V to the + side and the BRN/BLK cluster wire to the - side of an LED.

[sooprvylyn]

OK awesome.  I will see what wires I still have access to since I deleted my gauge cluster a long while ago.  I may still have the wire saved though.

Luckily I am pretty attentive to the working parts, especially coolant and fan function...and also have a manual override switch on a larger than stock fan, and a brand new thermostat....The coolant system gets a lot of regular attention from me(because I dont have a light yet).

I may be back with some images of the OEM wires I still have on the bike to see if you can confirm any BRN/BLK wire I might find that could be the one you are referring to.

[sooprvylyn]

Yes, the rad cap will blow before any engine damage. (248 F)

Might be a long shot, but is this the correct BRN/BLK wire(far right)? It's still in the connector, but not connected to anything atm.

BUT, once the rad cap blows you need to let the bike cool and refill the cooling system. Having a temp indicator (lights at 239 F on a K1100) lets you shut down the engine to let it cool before the cap blows. (I once did a long summer ride on a 93 K1100 with a bad fan and the temp light helped me keep the rad cap from blowing when I'd get stuck in slow traffic at 90+ F.)

On a K1100 you can wire up a temp warning LED with 12V to the + side and the BRN/BLK cluster wire to the - side of an LED.

Any idea if thisnis the correct BRN/BLK wire...top wire in photo?

[sooprvylyn]

More pics of this stock connector

[sooprvylyn]

I actually just cut this off of it last night...this was my label when I chopped the loom 2 years ago, but it's function was a guess at the time. I'm hoping i was correct and this is the wire I need to connect to negative lead on led light

[Laitch]

If it has continuity to #20 of the Motronic plug, it's the right wire according to the attached drawings from the Motronic manual downloadable from this site.

[frankenduck]

There's only one BRN/BLK wiring circuit on a 93 K1100. It goes from Motronic Pin 20 to both the diagnostic plug and the cluster temp warning light.

Diagram 3 here:
https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/kwiring/K1100LT.93/1993.K1100LT.Wiring.SLP.V2.0.pdf

[sooprvylyn]

Awesome. I think this is the one then.  Thanks for your help guys