Joined: 20th Oct 2009
Ride: EF Fairmont '96
I have a solution to those who want to use led tail / brake lights but also have a factory cruise control fitted. This solution deals primarily with EF / EL sedans but I imagine it would work across all models and makes of cars (differing only in wire locations and wire colours). I don't know if this is important enough to put in the tech guides but it is useful for some.
First with the problem. If you have a factory cruise control (unsure if aftermarket cruise would be affected similarly) when you fit led tail/brake lights you will find that the cruise control does not work when the lights are on. So no cruise at night (and if your like me and have your lights on during the day then no cruise at all) This is because a normal globe uses separate elements for tail lights and brake light where as a led globe set up uses each led twice with diodes (or resistors.. never taken one apart to see which) to cut current for tail light usage and full power for breaks. Because of this double usage a slight feedback gets sent back along the break wire when the tail lights are on tricking the cruise into thinking the break lights are on.
Now the solution. What you will need:
1 x 5 pin relay (12v 30amp)
5 x Female blade connectors
6 x Cable joiner (unless you like to solder)
1 x Wire tap connector
2 x in-line fuse (these fuses should be of the same amperage as what you will find in your fuse box for your brakes)
1 x Self tap screw (short)
Okay to start with the wire colours you are going to be looking out for are DG-R (dark green-red), Y (yellow) and BK (black(Earth))
First roll back the boot carpet to the back seats then remove the plugs in the side carpets and fold them back the same way. Now you are able to get at the wiring. There are a number of places to cut and join wiring but the easy method is the one I will use as per the diagram below(for those that want to run wires exactly the way they are already run I'm sure you can work out how)
Now start on the left. Peal back the electrical tape on the wiring to the first lug (lug being where the harness is clipped to the boot floor and make sure it's the car side wiring of the tail light plug). now locate the DG-R wire and cut it halfway between the lug and the plug. Tape off the wire just cut that leads back into the boot as you will not be using it again (but it will still have current running thru when the breaks are applied and you don't want to short it out). now strip the end of the wire that leads to the plug along with and uncut length of extra wiring and join them together (make sure to tape the join for extra strength). Now pull back the boot seal rubber as you want to run the wire from left to right under the rear panel capret. Measure out that length of wire so it can run comfortably about 2 inches above the earth (black wire) that is screwed into the right hand boot rib. Run the wire thru and replace the boot seal. Cut the wire and join your inline fuse then fit a Female blade connector to your inline fuse. plug this into the relay at one of the 87 numbered terminals.
Now locate the right tail light plug and strip the tape from that harness the same as on the left. Again cut the DG-R wire halfway between the plug and the lug. Strip both ends of the cut wire as you will be using each end of the cut shortly. Cut 1 piece of your extra wiring that will comfortably reach from the cut ends to 2 inches above the afore mentioned earth on the right rib and another that will be shorter to allow for the inline fuse length. start with the wire that runs from the plug and strip and join 1 of the extra pieces to that wire then join your in line fuse then fit a blade connector and plug it into the other 87 numbered terminal on the relay. Now do the same (without the need of an inline fuse here) with the other wire that runs back along the main harness and join that to terminal 86 of the relay.
Now cut an extra piece of wire that will reach from that point 2 inches above the earth to about halfway along the earth wire running back to the harness. strip one end of that wire and fit a blade connector then using the wire tap connector connect it one of the earth wires (doesn't matter which one) once you have done that connect that wire to terminal 85 of the relay.
Next part is a little tricky. locate the trailer plug harness connector. This will be a connector that runs from the right hand lug to under the rear carpet panel. If you do-not have a factory towbar and wiring this plug will connect to a plug that only two wires come out of (this is your number plate light plug) strip the tape off that harness from the plug back to the lug and locate the Yellow wire. Do-not cut yet. If you have the factory tow wiring you will have to splice into this wire by soldering not using a wire tap connector (it is a constant current wire and the wire taps don't handle that to well) however if you don't have the factory tow wiring then you will be able to cut this wire and join.. However still don't cut it yet. Find a point halfway between the plug and the lug then cut a piece of your extra wiring to reach from there to that same point 2 inches above the earth on the rib. Strip both ends of that extra wire and fit a cable joiner to one end and a blade connector to the other and plug it into the terminal numbered 30 on the relay. Get some electrical tape and rap it around the entire base of the relay now and all exposed metal connectors. Now carefully cut the yellow wire making sure whatever you use to cut the wire doesn't touch the body. Do-not let go of the yellow wire (the part that runs back along the harness) after cutting as if it touches the body it will earth and blow some fuses. Strip the end of the yellow wire and fit it to the wire you just made.
Make sure you have put tape around all joins for extra strength then get a self tapping srew (MAKE sure it is a short one that won't reach from the rib and touch the side panel) and fix the relay to the right hand boot rib at (you guessed it) 2 inches above the earth. Wire tie any loose wires making sure that the boot carpets will not be restricted when put back in place.
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