Thread: Labelling wiring and relays

Originally Posted by DoubleChevron

Ok I think I've worked it out .... All I can say is ... WHAT THE **** WAS LAND ROVER THINKING.... I couldn't make sense of the circuit at all..... so I went back to the standard land rover globe socket and checked the voltage.... get this .... It's the most bizarre **** I've seen in a long time. high beam and low beam ... reverse the polarity at the globe holder. You meter whips over to the negative range when you flick between the two.... WTF were land rover thinking... This is bloody crazy. So we have a crossover circuit for the relays to attempt to make sense of the bull**** land rover did with the headlight wiring.

Bugger me .... It would have taken me forever to workout a relay circuit for this if somene hadn't already done it I need to write this all down so I can figure out how it works... so low beam has earth as the earth, and 12volts at the power pin, then high beam flicks around, the earth pin becomes 12volts, and the high beam pin becomes earth .... bugger me ....

seeya,
Shane L.

Once you've worked it out, I have a '69 FIAT you can help with....

Originally Posted by johntins

Once you've worked it out, I have a '69 FIAT you can help with....

One of my other cars ... Is a Citroen CX2500 GTi Turbo my father imported from the UK. Imagine a car with 5 separate computers....trip computers, AEI computer, injection computer, ABS computer........ no starter relay, no headlight relays .... and wiring full of black rot from the salty soggy pommy roads. I've cut a lot of it back to the back of the engine bay and replaced it one wire at a time. Most pre-2000 car wiring is pretty simple if you do a bit of debugging and can understand the circuit (eg:series parallel fans circuits ) ... but gee's, land rover takes the cake with buggering up a simple light circuit

seeya,
Shane l.

Hi again Shane and are you trying to sort out the voltage polarity at one of the headlight plugs.

If so, the voltage does not reverse, you are simply measuring the voltage of the terminals back to front, and you are getting a positive feedback between low beam and high beam filaments.

A very common mistake.

NOTE, Land Rover have POSITIVE SWITCHED headlights

You will have three terminals in the headlight plug. Two vertical and one horizontal.

The HORIZONTAL terminal is your low beam positive ( 12v + ) terminal

The two vertical terminals are for high beam. One is positive ( 12v + ) when high beam is on, and the other is GROUND or EARTH ( 0v ).

Turn your high beam on and measure the voltage. If when you measure the voltage, your multi meter shows a negative number, EG -12.32v ( a minus " - " sign at the front of the number ), then you have your probes back to front.

You have the RED probe on the ground terminal and you have the BLACK probe on the 12v terminal.

Reverse the probes and then with the correct voltage reading ( no minus " - " sign at the front of the number ) The BLACK probe will be on the GROUND or EARTH terminal.

Note which terminal is the EARTH terminal and then switch your headlights to low beam. Simply note the colour of the wire connected to that terminal.

Now place your BLACK probe on the EARTH terminal and place your RED probe on the HORIZONTAL terminal and you should have a 12v reading, with no minus " - " sign at the front of the number.

Note the colour of each wire connected to what terminal, You now have the correct polarity for your headlight wiring.

Also note, the left side headlight wiring can be a different colour to the right side headlight wiring. So check and note the colours one both sides.

The colour codes here should be applicable:

Lucas wire colour codes for Land Rover

DL

No RRC came with headlight relays, blaming LR for that mess is just preposterous. Looks more like someone in the distant past tried to wire the relays so that selecting fog lights would automatically switch off the low beam. Since then various amateur smoke releasers have been busy stuffing thing up even more.

Originally Posted by drivesafe

Hi again Shane and are you trying to sort out the voltage polarity at one of the headlight plugs.

If so, the voltage does not reverse, you are simply measuring the voltage of the terminals back to front, and you are getting a positive feedback between low beam and high beam filaments.

A very common mistake.

NOTE, Land Rover have POSITIVE SWITCHED headlights

You will have three terminals in the headlight plug. Two vertical and one horizontal.

The HORIZONTAL terminal is your low beam positive ( 12v + ) terminal

The two vertical terminals are for high beam. One is positive ( 12v + ) when high beam is on, and the other is GROUND or EARTH ( 0v ).

Turn your high beam on and measure the voltage. If when you measure the voltage, your multi meter shows a negative number, EG -12.32v ( a minus " - " sign at the front of the number ), then you have your probes back to front.

You have the RED probe on the ground terminal and you have the BLACK probe on the 12v terminal.

Reverse the probes and then with the correct voltage reading ( no minus " - " sign at the front of the number ) The BLACK probe will be on the GROUND or EARTH terminal.

Note which terminal is the EARTH terminal and then switch your headlights to low beam. Simply note the colour of the wire connected to that terminal.

Now place your BLACK probe on the EARTH terminal and place your RED probe on the HORIZONTAL terminal and you should have a 12v reading, with no minus " - " sign at the front of the number.

Note the colour of each wire connected to what terminal, You now have the correct polarity for your headlight wiring.

Also note, the left side headlight wiring can be a different colour to the right side headlight wiring. So check and note the colours one both sides.

Thanks! It's quite bizare. That certainly doesn't appear to be the case. I unplugged the relays harness and the globes and measured the voltages.



This is what I came up with.

Low beam works normally. High beam seams to flick the polarity over. the earth pin becomes minus 12volts. The three relays (rather than two) then make sense of the polarity switching and drive standard high beam/low beam globes with the correct polarity. There is no extra wiring in there to pickup fog lights etc... It actually a fabricated relay harness that has a manufacture date of 1994 ... and plugs into the right hand front land rover headlight socket (the only connections are headlight socket and relay power). Very nicely done.

this is a 1993 Range Rover. Just to prevent the confusion. The company/person that made the relay harness did an excellent job. land rover sure did make things difficult for them.

I'll take a photo of it later so it makes sense. Including the model number of the relay harness.

I didn't need to touch any of this .... It does work... I just wanted to know why you would use 3 relays to switch headlights. It does however explain my problematic headlight switch issue. There is not enough current being drawn through the headlight switch to burn off/clean the low beam contacts in the new headlight switch. I probably should unplug the relay harness temporarily to give the new switches contacts and chance to heat up and work a bit.

seeya,
Shane L.

Originally Posted by DoubleChevron

One of my other cars ... Is a Citroen CX2500 GTi Turbo my father imported from the UK. Imagine a car with 5 separate computers....trip computers, AEI computer, injection computer, ABS computer........ no starter relay, no headlight relays .... and wiring full of black rot from the salty soggy pommy roads. I've cut a lot of it back to the back of the engine bay and replaced it one wire at a time. Most pre-2000 car wiring is pretty simple if you do a bit of debugging and can understand the circuit (eg:series parallel fans circuits ) ... but gee's, land rover takes the cake with buggering up a simple light circuit

seeya,
Shane l.

Oh, I hear you. I only mentioned FIAT because, in true Italian electrical tradition, it was "why use one one wire when six, or five, or seven, would do?".

Originally Posted by johntins

Oh, I hear you. I only mentioned FIAT because, in true Italian electrical tradition, it was "why use one one wire when six, or five, or seven, would do?".

They do better than that. Wait until you find the crimp on terminal "joiners" mid harness as your unwrapping it .... from which point onwards one wire becomes 5 wires full of black rott with a crimp on joiner joining the mess together. Cars from the mid 80's onwards are more painful too as every option available for every market is generally wired in the harnesses..... so you have dozens of "plugs" all over the car that have nothing to plug into .... or do they and it's unplugged

Oh, what sort of Fiat Sounds interesting, I like interesting cars

seeya,
Shane L.
PS: I know you are all waiting for my aplogy later tonight where I say "You guys were right as always, I'm I'm to stupid to read a meter properly :clown:".