Relay source wire

[lightwait26]

Looking to add a cooling fan relay to an S3, where be the best place to connect the permanent, unswitched hot lead?

[lotusfan]

Probably the best place would be the main battery connection on the starter solenoid on the firewall behind the carbs. There should be a spare tab on there. I think the solenoid connections point downwards on an S3 so may be difficult to get at. Don't forget a fuse!

[MarkDa]

If you don't mind it being unfused you could use the battery side of the starter solenoid.
Which doesn't preclude you using an inline fuse of course.
It's a good source for a highish load on right side of the car.

[alan.barker]

I use relays which have a fuse
Alan

[elanner]

It terms of neatness wouldn't it be better to power it from the F connector on the RB340 control box? Electrically it's the same place, but would avoid a stray "what-the-heck's-this?" cable hanging off the solenoid, and could be tidily integrated to the rest of the wiring system.

(Not that I even have a control box, the PO removed it when fitting an alternator and made a up a small distribution panel to replace it. My fan is powered from the panel.)

Nick

[lightwait26]

It terms of neatness wouldn't it be better to power it from the F connector on the RB340 control box? Electrically it's the same place, but would avoid a stray "what-the-heck's-this?" cable hanging off the solenoid, and could be tidily integrated to the rest of the wiring system.

(Not that I even have a control box, the PO removed it when fitting an alternator and made a up a small distribution panel to replace it. My fan is powered from the panel.)

Nick

I have essentially the same setup with my alternator. This would certainly be the easiest method.

I assume that you are referring to the terminal for the heavy output wire from the alternator ?

[lotusfan]

art

If you have an alternator, not standard on an S3, then the heavy output wire is a good choice and is very close to where you need the supply.

[elanner]

I assume that you are referring to the terminal for the heavy output wire from the alternator ?

Yes. There's nothing wrong with using the solenoid, of course. But for neatness and future maintainability I'd be keener to connect the fan closer to the main wiring hub rather than string a stray wire over from the solenoid. Depending on your fan controller you may also need to run an "enable" wire from the switched power, so that the fan will only run when the ignition is on. In which case it's tidy to keep both wires close together.

Nick

[MarkDa]

Deleted double post

[MarkDa]

The OP wants a permanent live supply - so wherever it comes from it can provide the feed to thermal switch from the relay end of the wire.
I used the same main feed wire for the air horns as well which with a double relay brought an added lightness to the wiring!
As well as having less wires to tie in or trace in the future.

[elanner]

The OP wants a permanent live supply - so wherever it comes from it can provide the feed to thermal switch from the relay end of the wire.
I used the same main feed wire for the air horns as well which with a double relay brought an added lightness to the wiring!
As well as having less wires to tie in or trace in the future.

Yup, right. But with my fan controller (a Derale 16759) there's a permanent live supply to the fan (which draws a high current). Then there's another low current wire from the switched (ignition) 12v that "enables" the controller. The controller monitors the thermal sensor and an under-the-dashboard override switch. The fan doesn't run when the ignition is off. Picture attached - there are lots of way to do this (note that the controller is on the ground side of the circuit, not the supply side, per Derale instructions).

Nick

Elan_FanWiring.pdf

(25.32 KiB) Downloaded 312 times

[lightwait26]

Thanks to all who have responded!

[Andy8421]

The OP wants a permanent live supply - so wherever it comes from it can provide the feed to thermal switch from the relay end of the wire.
I used the same main feed wire for the air horns as well which with a double relay brought an added lightness to the wiring!
As well as having less wires to tie in or trace in the future.

Yup, right. But with my fan controller (a Derale 16759) there's a permanent live supply to the fan (which draws a high current). Then there's another low current wire from the switched (ignition) 12v that "enables" the controller. The controller monitors the thermal sensor and an under-the-dashboard override switch. The fan doesn't run when the ignition is off. Picture attached - there are lots of way to do this (note that the controller is on the ground side of the circuit, not the supply side, per Derale instructions).

Nick

Elan_FanWiring.pdf

Nick,

I wouldn't consider that circuit to be best practice. Fuses can be used effectively in many places in a circuit, but in a car application, it is best to have the fuse upstream of the device and wiring being protected. In your attached diagram, the fuse will protect against an over-current event in the fan, but parts of the circuit and the fan itself are unfused in the event of a short to earth. Not as likely in an Elan as a normal metal bodied car, but still possible. It would be better to have the fuse as close to the point of supply as possible.

Andy.

[elanner]

Andy,

I agree, your suggestion is what I would do if starting from scratch. However the controller that I've been referring to comes with a good quality, nicely built loom that is set up per my previous diagram. So I had the choice of ripping it apart and putting the fuse nearer the power source or just trusting the folk at Derale. I chose the easy option!

I have to say that I like the idea of running 12v directly to the powered device and then having all the unreliable stuff - connectors, fuse blocks, relays - controlling the ground.

Anyway, for completeness, here are the Derale installation instructions and installation kit.

Nick

[MarkDa]

It's certainly an impressive product.
Whilst I agree that in principle fuses should be as early in the run as possible if presented with a prefabricated kit I too would go with it as standard overload conditions are catered for.