When I got the car, the dim-dip lighting did not work for one of the headlights. For UK cars, this brings on the headlights on at a low level when the ignition is on and side lights are switched on. This has been a legal requirement since 1987 here.
After some investigation, I found the headlight control unit under a removeable panel by the LHS suspension top in the engine bay. This connects to a small metal box at the front of the suspension top (on a plate welded to the bracing). This box gets incredibly hot. It turns out that this is just a box with some high power resistors in. Sadly only one chain of resistors was working (I dread to think how hot it gets when all the resistors work).
I had to open up the headlight control unit box to unsolder two wires (and remove a little black tape from the loom connected to it) to extract this resistor block. I assumed I could just replace the failed resistor, but sadly the manufacturer (not Rolls) had chosen to pot the whole thing internally with epoxy. Great!
Anyway, to fix this item, I decided to use a little more finesse and build a small chopper circuit that would produce the desired reduced output from the headlights by switching the current (chopping) on and off quickly in bursts. In this way, almost no heat is produced and the system is much more efficient. My rats nest bench prototype works well and I've now progressed that to a buildable item that will fit in a small aluminium box in the same place as the original. Its a lightly chunkier, but it should work fine. I bet its a lot cheaper then a new headlight control unit to which this attatches.
Hopefully this will fix my problem and I can move onto the next fix. I'll post more info when I've installed this on the car. I'll take some photos too.
Cheers... Rob.
After some investigation, I found the headlight control unit under a removeable panel by the LHS suspension top in the engine bay. This connects to a small metal box at the front of the suspension top (on a plate welded to the bracing). This box gets incredibly hot. It turns out that this is just a box with some high power resistors in. Sadly only one chain of resistors was working (I dread to think how hot it gets when all the resistors work).
I had to open up the headlight control unit box to unsolder two wires (and remove a little black tape from the loom connected to it) to extract this resistor block. I assumed I could just replace the failed resistor, but sadly the manufacturer (not Rolls) had chosen to pot the whole thing internally with epoxy. Great!
Anyway, to fix this item, I decided to use a little more finesse and build a small chopper circuit that would produce the desired reduced output from the headlights by switching the current (chopping) on and off quickly in bursts. In this way, almost no heat is produced and the system is much more efficient. My rats nest bench prototype works well and I've now progressed that to a buildable item that will fit in a small aluminium box in the same place as the original. Its a lightly chunkier, but it should work fine. I bet its a lot cheaper then a new headlight control unit to which this attatches.
Hopefully this will fix my problem and I can move onto the next fix. I'll post more info when I've installed this on the car. I'll take some photos too.
Cheers... Rob.