Temperature Control Relay

[Eman24]

My 1990 K75 Fan does not come on. Recently, the bike stalled after being in gridlock conditions for about an hour. It stuttered and stopped. And after cooling off for a bit, it started up just fine.

I've idled the bike for up to 20 minutes and the fan won't come on. I had a new temperature sensor installed about a year ago when it tested negative. At that time the mechanic also checked the thermostat and water pump impeller.

Yesterday I jumpered the contacts on the harness side of the relay and the fan comes on. The same is true for the temperature warning light. I've taken resistance readings on the two points that connect with the bimetal switch. With the bike cold the reading was 2807 ohms, and with the bike warmed up for about 3-4 minutes 1021 ohms. I should probably do it again with the bike fully warm and see if the resistance goes down to the levels it should to turn on the fan. But assuming that it will, what else should I check before purchasing a new relay ?? Or is there a way to check the relay itself ?

Thanks very much!

[BuddingGeezer]

The fan works, the temp semsor show falling resistance when warming. The culprit is the fan switch located in the relay box under the fuel tank.

Since you have eliminated the other 2, remove the plug from the temp sensor and ground it. You may have to try both wires in the plug, 1 grounds the fan, 1 goes to the fuel injection computer. You must have the ignition on and press the starter button. If the fan is good, the temp sensor good and the fan does not come on, it's the fan switch(relay).

BTDT.

Ralph Sims

[Eman24]

The fan works, the temp semsor show falling resistance when warming. The culprit is the fan switch located in the relay box under the fuel tank.

Since you have eliminated the other 2, remove the plug from the temp sensor and ground it. You may have to try both wires in the plug, 1 grounds the fan, 1 goes to the fuel injection computer. You must have the ignition on and press the starter button. If the fan is good, the temp sensor good and the fan does not come on, it's the fan switch(relay).

BTDT.

Ralph Sims


Thank you very much!

[BuddingGeezer]

Before you spend $60 for a fan switch, I assume all the fuses are good. Since the bike runs, the fuel injection relay fuse is good, #6 I think. this is the power for the fan relay trigger. The fan gets it's power from the horn relay fuse #7 I think. Does your horn work? If not that may be why your fan doesn't.

Ralph Sims

[Eman24]

Before you spend $60 for a fan switch, I assume all the fuses are good. Since the bike runs, the fuel injection relay fuse is good, #6 I think. this is the power for the fan relay trigger. The fan gets it's power from the horn relay fuse #7 I think. Does your horn work? If not that may be why your fan doesn't.

Ralph Sims


Interestingly, every once in a blue moon the horn stops working, but it's a loose wire from the relay to somewhere in the harness. It doesn't seem to be at the connector. The fuses are all fine, however. Thanks again!

[Eman24]

Before you spend $60 for a fan switch, I assume all the fuses are good. Since the bike runs, the fuel injection relay fuse is good, #6 I think. this is the power for the fan relay trigger. The fan gets it's power from the horn relay fuse #7 I think. Does your horn work? If not that may be why your fan doesn't.

Ralph Sims

Well - Just won a fan switch relay on Ebay from a local parts shop for 9.99. Tomorrow I guess I'll let it idle and pray !

Thanks again,
Elliot