S1.5 fans come on when bonnet closed !

[genneton4]

Hi Forum.
When I start my S1.5 from cold with the bonnet open all is well.
When I start my S1.5 with the bonnet closed the fans come on with the ignition ??
Surely they should only come on when the engine is too hot (which they do, when the bonnet is open).

There seems to be a 'little black box' in the mouth of the air intake which has a wire going back to the fans !

Can anyone shed any light on what's going on ? It's an American car.

Thanks

Keith

[Philk]

Hi.... Does your car have an "otter switch" on the top of the header tank? If so, this could be shorting across its terminals when the bonnet is closed thereby closing the circuit and causing the fans to switch on. I am not sure what the device is you have in the mouth of the bonnet but the fact that the problem only occurs when the bonnet is closed is pointing to that physical action causing the switch that drives the fans to activate

[Geoff Allam]

Gravity switch?

[MarekH]

A quick check of the circuit diagram shows that the fan, like the wipers, are live whenever the ignition is on. This means anything which contacts any of the wires after the fan is capable of providing the earthing path to complete the circuit. I'd check the integrity of your wiring between the fan and the Otter switch.

The bonnet itself is a possible earth path so if any of the return wiring frays against it, the fan will run.

A more sensible wiring scheme is that on the s3. This uses a relay powered from a fused brown wire, so the fan current doesn't run through the ignition switch - only the tiny relay winding current does. The s3 Otter switch also has an easier time - it only switches the relay winding current - yours has the full fan current coming through both switches and that wear and tear may make one or the other fail prematurely.

kind regards
Marek

[Robsan]

The otter switch should be in the front of the radiator header section and has a single wire connection. The other end of the wire goes to a fan relay mounted on or around the picture frame. The purpose of the wire/ otter switch is to connect a negative [ground] to the fan relay

it appears in your case that closing the bonnet makes that ground connection, switches the relay on and energise the fans. Opening the bonnet removes that ground connection !! shouldnt to too difficult to locate the problem....................... best of luck

[genneton4]

Just for completeness. You were all correct.

Being a S1.5 it is an S2 rad. The otter switch is in the front of the rad. I couldn't see this without a mirror on a stick.
When the bonnet was closed it did indeed short the otter.
In the USA, somebody had 'creatively' altered the feed so that it had two long (near 1 inch long !) female bullet type connectors to the otter that had rubbed through the feeble insulation exposing the wires.

Re-insulated the wires, slightly bent the bullets and also altered the rad stays to be adjustable toward the engine for maybe 1/4" inch.

All is well.

I think the little box in the nose is something was maybe a 'herring rouge' left over from an old alarm system that I have removed.

Thanks

Keith