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Wiring question - ignition switch controlled earth ?

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joncat

Member Since: 19 Mar 2016
Location: Bridgend
Posts: 16

2005 Discovery 3 TDV6 S Manual Zermatt Silver

Wiring question - ignition switch controlled earth ?

Hi all,
Further to my update on my recent post regarding the blowers does anyone know if there is a cable I can connect to going to the engine bay fuse box that is an ignition switched earth ?

IE Only goes to earth when the engine is running / ignition on ?

Thanks in advance !

20th Feb 2018 3:55 pm

TigerRecovery

Member Since: 31 May 2017
Location: Long Stratton, Norwich, Norfolk
Posts: 901

2016 Discovery 4 3.0 SDV6 Landmark LE Auto Waitomo Grey

There's no such thing on these cars as an Ignition Switched earth. Only the power is switched. In the ecus they will switch to ground to activate solenoids etc, but there are no feeds that provide an earth that is only there with ignition on.

Why do you need it? You could use a relay that is switched via the ignition to control the earth with a permanent live, but it is usually safer to have a switched live. 1972 Range Rover Classic 2 door V8
2013 Land Rover Discovery 4 HSE - SCRAPPED
2016 Land Rover Discovery 4 Landmark
2022 Volvo XC40 T5 PHEV 282HP FWD 3 cylinder!

20th Feb 2018 4:12 pm

joncat

Member Since: 19 Mar 2016
Location: Bridgend
Posts: 16

Thanks for the reply - I need it to turn the heater fan on, the original cable no longer provides the earth, don't want to rip the car to bits so hoped to piggy back an earth in the eb fusebox.

So that when the ignition is on / engine running I can use the blowers...

20th Feb 2018 4:17 pm

Pete K

Member Since: 15 Jan 2016
Location: GL
Posts: 10766

2005 Discovery 3 TDV6 HSE Auto Rimini Red

you could try using the brown wire to the heated mirror relay. They seam to be stuck on all the time the ignition is on, and should get you thru the winter as a minimum.

20th Feb 2018 5:40 pm

joncat

Member Since: 19 Mar 2016
Location: Bridgend
Posts: 16

Okay I will try that thanks for the input : )

I have just had SOME success by rigging up a relay : using an ignition on +12V from the FB to switch a and supply the NEGATIVE "return" that triggers the blower relay - PHEW !

I do however now get a gentle blower fan rotation when the blowers are off - as long as the ignition is on, but I can live with that.

I will try to pick up the brown wire you suggested and report back in the morning

Will not doubt be a bit neater

20th Feb 2018 5:58 pm

joncat

Member Since: 19 Mar 2016
Location: Bridgend
Posts: 16

Update

Okay - so I tried to neaten the job by using the -12v brown "feed" to the relay for the heated mirrors.

Seemed okay until I turned the ignition off then all hell broke loose with the hazards flashing repeatedly and the central locking erupting !

So I have gone back to using a relay triggered by the positive to the rear blower relay.

Only downside is a whoosh on ignition on and despite the blowers being tuned off and the display glowing off the blower runs at slow speed after the ignition is off for around two mins or so.

I can live with that.

I will survive until easter or so and run a new feed from the back of the control panel to the relay.

Back to my diy relay switched hack for now !

22nd Feb 2018 10:19 pm

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