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1995-2002 Range Rover P38A
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Discussion Starter #1
Hi,
Does the P38 have the facility to run automatic headlights (i.e. dipped beam on during darkness automatically)?

I’m assuming not as the Electrical Trouble Shooting manual only references daytime running lights for certain markets (which are on all the time when the engine is running) but does not mention ambient light sensitive switching.

If not, has anyone fitted one of the aftermarket kits?

I know I’m potentially making a complex car even more complicated, but it’s about the only feature I miss on the ’38 compared to my day-to-day Freelander LR2, which I guess goes to show how advanced the P38 was when it came out.

I'd appreciate any pointers, particularly in avoiding the BeCM getting confused with bulb failures and the like...

cheers
 

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1995-2002 Range Rover Classic
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p38 does not have the capability of auto dipped headlights, you can program the becm to run daytime running lights. as far as add on kits, I'm sure someone has something out there. I have found aftermarket kits for what ever function, normally have strong points on some features but lack on others
 

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I was recently asked if it could be done and, having looked into it, it should be fairly simple. You'd need to apply a ground signal to both the sidelight and headlight output from the light switch (as it needs the sidelights to be on to switch on the rear lights too). You'd need to put blocking diodes in to stop things getting confused and to allow the light switch to work as normal and a switch to enable auto lights. The other thing I considered was whether it would be possible to use the sunlight sensor already on the top of the dash for the HEVAC as the sensor to trigger the lights but didn't get as far as checking the signal from it to see if it would work. That would save having to fit another sensor.
 

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That's just setting Daytime Running Lights to Enabled in the BeCM but that means they are always on. I was asked by someone that lived near to a couple of tunnels where signs said to switch your lights on as you entered the tunnels and off again once you were out. He was always forgetting to switch them off again so thought about automating it. I suppose now that a lot more cars have DRLs as standard there's less chance of being flashed by other drivers as you've got your lights on in daylight but while it isn't necessary why do it?
 

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1995-2002 Range Rover P38A
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Discussion Starter #6
Hey Richard,

Thanks for that - I'd not considered the HEVAC sun sensor - this is particularly interesting as it's a known part from a known source - not only does it potentially simplify the installation, but the sensor is easy to source if it fails (something that can be difficult with kits, where spares are often not easy to find)

I've spoken to a colleague who is far more clued up on electronics than me and he assumes the sun sensor is fed with a stable voltage input, and a variable voltage output, which the HEVAC ECU is comparing.

The dash is due out soon to change the heater unit, so I'll do some voltage tests on the sun sensor circuit and determine the output voltage at the right light level for the headlights (dusk)

Apparently, once I've done that, it's a simple piece of logic electronics to trigger a grounding of the respective light circuits at the determined voltage, turning them on when it's dark.

I'll let you know how I get on :wink:

cheers for the feedback.
 

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Not sure if the sun sensor is sensitive enough, looking at the HEVAC signals with Nanocom and it looks like it might only be able to tell the difference between direct sunlight and shade. that's why I was going to have a look at the output and see if it would be possible to use it. You'd also need to incorporate some hysteresis in the switching or you could end up with headlights that switch on automatically as it gets dark but then switch off every time you drive past a streetlight or shop with bright lights outside. It was one of those projects I was asked if it was possible and then having concluded that it was, never went any further. The guy that asked has moved house now so no longer drives through the tunnels twice a day so it isn't needed any longer.
 

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1995-2002 Range Rover P38A
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An interesting project.
I have watched the live data from the sun sensor, and it appears to be a pretty wide range radiometer and it does give readings in Watts / Square Meter as it should.
It is not too sensitive, or true to real world readings, but should give an adequate response for lights on, without false triggering by street lights, etc.
When designing the circuit, add a simple timer loop for "Off" and make it long enough to assure no false triggering. So, exit tunnel, wait a couple of minutes, then off.
 

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1995-2002 Range Rover P38A
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I have automatic headlights on mine :)

Retrofitted a unit to do it - works very well.
 

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1995-2002 Range Rover P38A
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I fitted one of these from good old China - it came as is, so needed a little enclosure for the board to live in. The sensor currently appears next to the solar sensor, its cable wedged up the side of one of the windscreen vents from underneath. I hardly notice it there - though I'm sure it could be tidier.

https://www.ebay.co.uk/itm/Automatic-Headlight-Sensor-Light-Delay-Control-Module-Light-Modified-Adjustable/172312982513

The unit needs +12v, which I feed via a custom latching dash switch (made up from a front fog cover and I think EAS inhibit switch, not 100% now) which is in the blank position where the Low/High transfer switch would be on a manual. It is fed from an accessory supply and the switch backlight is connected to the illumination circuit like any other switch. This way, when I turn on accessory circuit - yes, the lights come on if it is dark, but they go off during cranking. If I have the accessory circuit on for a prolonged period (sat with radio on, etc) in the dark, I can just push the button to turn the lights off.

The output of the module is relay contacts- NO/NC. As the inputs to the BECM need grounding, I'm switching ground to the dipped beam input. Thus I can still use the original headlight switch to turn the lights on if I want, or I could leave the sidelights on, and the module would turn on the dipped beams as it got darker. Normally I just leave that switch off entirely though.

The light level it comes on at is adjustable, as is the 'off' delay - so you can tune how often it switches quite well. I could probably do with making mine a little less sensitive and stay on for a little longer at some point. The module itself lives behind the dash switches. Been in there a couple of years now and no issues.

I can take some pictures of it in situ if interested.
 

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My objection to automatic headlights is that they don't turn on in fog as it is still light. That's why you see so many BMW and Audi drivers driving around in fog with no lights on, manually operating a switch is far too primitive for them. They are a good idea if you need to drive through tunnels where they tell you to switch your lights on meaning you forget to switch them off but for the rest of the time, as you say, there's a switch on the dash that does the job nicely. But I can see if you have got used to them in another car then it is something that you might miss. It's also something else to go wrong, my partner has a Merc and she has always left the switch in the Auto position but it has now decided it is dark all the time so they come on as soon as the ignition is turned on, even in bright sunshine!
 

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1995-2002 Range Rover P38A
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That's the thing - in my 5 series, I have auto wipers (almost useless) and auto headlights - and I like the functionality.

But then, I'm also able to tell when they're needed despite it still being 'light' too, so manage to turn them on then too ;)

Actually in the 5, they're linked to the auto wipers too - after a couple of successive wipes, it will turn the headlights on, which is nice. Of course - this kind of functionality only works if it hasn't been turned to off. Don't get me started on the BS that is daytime running lights... the number of people I see driving around with DRLs on at night with no rear lights... not helped by the fact it seems the dashboard in modern cars is always lit up. Part of me blames the drivers, but I also can't help but wonder why rear tail lights weren't mandated to be included in the front DRLs, to account for the idiots so we can at least see them from behind?

Annnnnnnyway. Should you want auto dipped beam on a P38 - that's how I've done it, and another look on ebay shows there are quite a lot of units now available that work in the same way.
 
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