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Add Otter Switch for Fans


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Has anyone here run a switch to the fans in order to keep them on when you decide?  Can someone tell me how I would go about wiring this setup for my S4s?  I'm wondering which wires I would have to tap into.

THanks,

Ed-

'95 S4s

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I don't have circuit diagrams here ... if somebody has them, it'll make the job easier but it can be done without them.

First, locate the fan relay and remove it ... secondly, locate the terminals marked 85 and 86 ... these are the low power terminals that energise the relay.

To engage the relay, there needs to be 12v across these terminals. It could be wired in one of two ways, the EMS will either switch the +12v side OR the 0v side to activate the relay. I don't know which without the circuit diagrams.

With the ignition on and engine cold (below fan temp), check terminals 85 and 86 to a known ground point using a DC voltage setting on a multimeter.

If either terminal 85 or 86 are at +12v, the EMS is ground switching and you will need to add a switch from the other terminal (ie not the +12 side) to ground to activate the fans. (If both terminals read +12v, you've probably forgotten to remove the fan relay while testing!)

If neither terminal is +12v, the EMS is switching +12v to energise the relay. You need to work out which of 85 and 86 is connected to ground using the resistance setting on your multimeter, and connect the other (non grounded) terminal to +12v via a switch.

In either case, stick a 2 amp fuse in line with the switch to protect it if you get the wiring wrong!

That should do the trick! If anybody has circuit diagrams, they should be able to make it a bit easier by quoting wire colours!

Steve

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Steve-

Thanks for the reply. I'm a real beginner at this so I apologize for any stupid questions(Linguistics Major). 1st) where would I locate the fan relay? 2nd) Terminals 85/86, are located where? 3rd) When underneath the Esprit, I can easily access the three SPAL fans(aftermarket), and can see where the wires engage the fans. Could I just tap into those wires and run my new wire into the Esprit (I would then bring it into the binnacle where there is one unused button (Europe only button)??

Ed-

I don't have circuit diagrams here ... if somebody has them, it'll make the job easier but it can be done without them.

First, locate the fan relay and remove it ... secondly, locate the terminals marked 85 and 86 ... these are the low power terminals that energise the relay.

To engage the relay, there needs to be 12v across these terminals. It could be wired in one of two ways, the EMS will either switch the +12v side OR the 0v side to activate the relay. I don't know which without the circuit diagrams.

With the ignition on and engine cold (below fan temp), check terminals 85 and 86 to a known ground point using a DC voltage setting on a multimeter.

If either terminal 85 or 86 are at +12v, the EMS is ground switching and you will need to add a switch from the other terminal (ie not the +12 side) to ground to activate the fans.  (If both terminals read +12v, you've probably forgotten to remove the fan relay while testing!)

If neither terminal is +12v, the EMS is switching +12v to energise the relay. You need to work out which of 85 and 86 is connected to ground using the resistance setting on your multimeter, and connect the other (non grounded) terminal to +12v via a switch.

In either case, stick a 2 amp fuse in line with the switch to protect it if you get the wiring wrong!

That should do the trick!  If anybody has circuit diagrams, they should be able to make it a bit easier by quoting wire colours!

Steve

<{POST_SNAPBACK}>

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Steve-

Thanks for the reply.  I'm a real beginner at this so I apologize for any stupid questions(Linguistics Major).  1st) where would I locate the fan relay?  2nd) Terminals 85/86, are located where?  3rd)  When underneath the Esprit, I can easily access the three SPAL fans(aftermarket), and can see where the wires engage the fans.  Could I just tap into those wires and run my new wire into the Esprit (I would then bring it into the binnacle where there is one unused button (Europe only button)??

Ed-

<{POST_SNAPBACK}>

1) I don't know where your fan relay is. It may be covered in the drivers handbook - I know it is in my Excel manual, not sure about the Esprit. I think they changed the wiring so wouldn't like to tell you which one based on my late V8 - it could be wrong.

2) Terminals 85/86 are numbered connections to the relay. The will almost certainly be marked on the relay, and maybe on the relay socket too. Most relays will have those numbers, so the presence of that number doesn't mean you've found the correct relay ... use the manual for that!

3) Connecting directly to the fans requires a much higher rated cable, you will then need to connect up to a higher power +12 ignition switched feed too. I'd avoid this mainly because it needs high power cable, high power fuses (one per fan ideally) and a switch capable of around 40 amps!

Hope that helps,

Steve

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1) I don't know where your fan relay is. It may be covered in the drivers handbook - I know it is in my Excel manual, not sure about the Esprit. I think they changed the wiring so wouldn't like to tell you which one based on my late V8 - it could be wrong.

2) Terminals 85/86 are numbered connections to the relay. The will almost certainly be marked on the relay, and maybe on the relay socket too. Most relays will have those numbers, so the presence of that number doesn't mean you've found the correct relay ... use the manual for that!

3) Connecting directly to the fans requires a much higher rated cable, you will then need to connect up to a higher power +12 ignition switched feed too. I'd avoid this mainly because it needs high power cable, high power fuses (one per fan ideally) and a switch capable of around 40 amps!

Hope that helps,

Steve

<{POST_SNAPBACK}>

Regards

Mat

post-1-0302470001278592957.jpg

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Alternative method.............

Why not tap into the existing wires on the otter switch? Bring each wire back under the car (follow clutch hose) up through bonnet and back into dash. Then put on a switch. Bypasses the otter switch at will, uses existing wiring/relay. This is what I've done with my S2. Used the rear window demister switch so that I'm not drilling new switches into the dash (never used/needed rear window demister).

Regards

Mat 79 S2

Regards

Mat

post-1-0302470001278592957.jpg

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s4s=no otter switch. fed from ecu.

good idea though. did that on my excel too.

Alternative method.............

Why not tap into the existing wires on the otter switch? Bring each wire back under the car (follow clutch hose) up through bonnet and back into dash. Then put on a switch. Bypasses the otter switch at will, uses existing wiring/relay. This is what I've done with my S2. Used the rear window demister switch so that I'm not drilling new switches into the dash (never used/needed rear window demister).

Regards

Mat 79 S2

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When energising the fan relay with an additional switch and positive 12 V supply would it not be a good precaution to put a diode in the relay 12V supply coming from the ECM? You woulnt want to back feed into the ECM and fry it.

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When energising the fan relay with an additional switch and positive 12 V supply would it not be a good precaution to put a diode in the  relay 12V supply coming from the ECM? You woulnt want to back feed into the ECM and fry it.

<{POST_SNAPBACK}>

Does the S4S ECU +ve switch the fan?

If so, there's certainly no harm in putting a diode in there, but how would it back feed the ECM and fry it if the +12v for the override switch is ignition switched?

My Excel has diodes to the fan relay, but I thought that was primarily so that the otter switch doesn't cause the A/C compressor clutch to cut in!

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