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MG MGB GT V8 Factory Originals Technical - fan otter switch and relay

Im puzzled by how the connections go on to the relay cant seem to get the fans to run except by short circuiting them. Am i right in saying that the otter switch just makes an earth connection. Does any one know what colour wire goes on which number.

Cheers Dean.

Correct. An easy mod is to splice that wire via a switch to earth as a manual override.
Check circuit diagram in manual for correct relay connections.
Dave Wellings

Ill have to check but I just wired mine up via the factory setup and it works fine. Ill get a schematic drawn up and emailed to you if you fire me off an email.

The ground from the Otter switch (so-called because it switches on as the coolant gets 'otter) on the black/orange operates the relay which has a green wire (fused ignition) on the other side of its winding. The brown (unfused always hot) on one side of the contacts is then fed through to run the fans on the black/green. The green ensures that the fans always switch off with the ignition, even if the Otter switch is still closed.

The black/orange and the green should be on the W1 and W2 contacts of the relay, doesn't matter which, and the brown and black/green should be on C1 and C2, again either way round.

That is how my RB is wired, which doesn't agree with the circuit diagram in the Workshop Manual supplement, which shows a three-terminal relay and no brown wire.

With the ignition on and the Otter off you should see 12v on the Otter wire, and that confirms continuity from the green fuse through the relay winding right to the Otter. Grounding that should operate the relay and run the fans. If not check you still have 12v on the green at the relay, it could have a bad connection or the relay could be bad.

I presume you mean you are short-circuiting two contacts at the relay to get the fans to run, short-circuiting the fans would do nothing unless the relay were already operated, and then it would cook the wiring!

For a manual override just piggy-back a wire from a switch with a ground on the other side of it to the black/orange connection on the relay. Dave's suggestion of "splicing it via" means something else to me, may just be a difference in terminology. If you use an illuminated switch it will even tell you when the Otter has closed.
Paul Hunt

Eceellent paul what was throwing me was that i have seen the factory wiring diagram with only three wires.

Cheers Dean

This is how I did it, just as Paul explained, he also has a great diagram on his website of the wiring. I modified it for my own reference with a manual switch and light. The light comes on both when the fans are manually activated and when the otter closes the circuit.

This thread was discussed between 09/03/2004 and 10/03/2004

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