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I have drawn this circuit for my S4 radiator fan installation. Decided to go for a fan over-ride switch and lamp. The lamp will also light to tell you the thermostatic control has cut in. Tried it all on the bench and it works a treat. Fan operates only with ignition on. Hope this helps anyone in a similar situation.

William2 wrote:I have drawn this circuit for my S4 radiator fan installation. Decided to go for a fan over-ride switch and lamp. The lamp will also light to tell you the thermostatic control has cut in. Tried it all on the bench and it works a treat. Fan operates only with ignition on. Hope this helps anyone in a similar situation.

Circuit is fine.

It is personal choice but the only difference I would make is to fit a self healing thermal breaker rather than an inline fuse. It was certainly something that MG instigated way back in the 70's with their electric fan installations and what I have included.

The problem with fuses is few understand fast/slow blow types and how and where they should be used anyway.

Regards

Steve

How did you decide on the 10A fuse (or thermal cutout if you decide to take up Steve's recommendation)?

Cheers

Robbie

The only point I would make is that these circuits typically take a clean 12v directly to the fan and then all the switch/relay/fuse stuff controls the ground. In other words, your diagram but backwards/inverted.

With your current diagram if anything around the fuses/relay/connectors touches a ground then it's going to short the battery and be a fire risk (the fuses obviously help prevent this, depending on the short). However, wired the other way around if *anything* shorts out then the fan will be in the circuit and the worst that can happen is that the fan comes on.

For a small circuit like yours then it probably doesn't make a lot of difference, but it's a thought. Far in the future, when you've forgotten how it's wired and you're digging around fixing some other problem you might be thankful when the fan suddenly turns on rather than a big flash!

I'm certainly no expert, so hopefully somebody will correct me if I'm wrong. But from casual observation this seems to be standard practice, and was how the circuit diagram provided with my Derale fan controller arranged things.

Nick

I decided on a 10Amp fuse because the fan I have fitted is rated at 80 Watts. An 8Amp fuse might be better.

Thanks William