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Good morning everyone. I have a 1978 MGB with a mystery wire that is in the loom that goes to the temperature sensor. It is a heavier gauge than the temp sensor wire, but is also dark green. It has power after the key is turned on. Anyone know where this might go?
well the car does have an electric cooling fan. but since it is hot after the ignition is on, that would mean it was on all the time.
The vehicle does have a electromatic switch at the radiator that I assume would control the fan.
IIRC, that heavy green (+12V) goes to one side of the fan and the "Otter" switch (in the radiator) has the other side at the fan and one to ground. Those should be black, I believe. When the Otter switch closes it supplies the ground leg of the fan circuit.
Disclaimer: This is from memory, haven't worked on that version MGB in a while. These guys: Advance Auto Wire have wiring diagrams for the MGB at every change point in production. Look through and find the year and compare.
Just looked thru the schematics and the Otter switch was introduced in '77 from the looks of it. It does supply the ground leg to the fans, that heavy green one should indeed be the voltage supply side for them. The diagram calls the Otter switch a thermostat.
There ~should~ be an Otter switch IN the radiator, at the back top starboard side. Round thing about the diameter of a US quarter-dollar coin. Two male spade connectors. Black wires connected, one goes to a ground point, the other to the fans.
Short it how? At the switch? If that's the case, likely the switch is bad. But those green wires to it must have been "added" along the way. There should be NO voltage through the switch, BTW. It should strictly be a grounding device. Voltage should be supplied to the fans with your errant green wire. Have you checked to see if the power is being routed thru the switch? A V.O.M. would be a good thing to have. A 12V test light would work, too.
Svc said:
yes I have that switch and it already has two green wires coming from it. Could this mystery wire plug into the fuse box somehow?
ABSOLUTELY NOT!!! That ~IS~ the fan's "hot" lead. As stated above, the Otter switch is a grounding device. Running +12V thru it is wrong. If the switch body contacts a ground (like if the rubber retainer had a spot where it has been rubbed thru) you could have a dead short. It's a thermocouple device. Bi-metal strip inside.
Yes I shorted it out at the switch, and the fan turned on. You might be right about the switch needing to be replaced. However that still doesn't help with the mystery wire. Would it go to the fuse block? Here is a pic of mine
If that is the fans "hot lead" then where does it plug into? If you look at my switch on the fan, it already has two wires coming from it. There is no other place to plug this wire into. Not that I can see anyway
Someone has been "creative" in the past, from the looks of it. Can you put a test light on the wires at the switch one at a time to see if one of those is "hot"?
Looking at the diagram, you have it correctly wired, that errant green wire is now a mystery to me as well.
If that is the fans "hot lead" then where does it plug into? If you look at my switch on the fan, it already has two wires coming from it. There is no other place to plug this wire into. Not that I can see anyway
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