I am starting the re-assembly of the dash and steering column. I am making use of the opportunity to sort out a few little issues.

I did not have a map light and someone had simply chopped off the wires and wired the legend strip to the Map switch. I have fitted a new map light and now I want to use the original wiring to connect it.
I have located the correct Purple Light Green wire which emerges just under the (horn?) relay. There are 3 wires together. The Purple Light Green and 2 black wires. One of the black wires is connected to ground the other isn't. Any idea what this second black wire is (the one not connected to ground)? Can I just assume because its black I can connect it to earth? It a "newish" wiring loom but a correct one.

I have the wiring diagram but that doesn't really help.

 

shown in the picture is not the Horn relay but the Lucas Turn Signal Flasher.
**I forgot what model and year is your car.

 

Just saw that too, turn relay. Mine is a '65 3.8 MOD. Converted at some point from RHD to LHD.

 

MK-2 or S type ?

in my 3.8 S type LHD, the turn signal flasher terminals are oriented to the left towards steering wheel.

 

Mk 2

 

Different set up on the S Type to the Mk2 but the map light wiring is the same. Purple green for live and black as earth or ground. All black wires should be earth but I have no idea what that second earth/black wire is for. Is there no continuity to earth on this wire?
In this photo you can see the purple and green wire with the black earth hanging down from the front of the turn signal relay wrapped in black electrical tape ending in spade connectors. The live purple and green spade connector is also covered in insulation tape as the map light had been disconnected prior to my strip down.

 

No continuity on the second black wire. There is a very low voltage on it but I guess that is probably just induction.

 

Do the two black wires link together at this point as a loop? Does anything else seem to not work that might be missing an earth?

 

No they are not connected. I will just leave it loose for now as it is easy to get to and wait and see if anything has stopped working.
I was also wondering if it was designed as a loop. I could just join them together at the bullet connector. They are the same length so maybe that was the intention.

 

Little victories. Having the map light working correctly, the legend lights, replaced the main illumination bulbs with LEDs so now I can see the instruments at night, side lights and fog lights switch on as designed (light switch didn't work well and the FogRanger connections were all messed up), clock ticking away and my wonderful new burl walnut. Now just have to figure out how to tighten that last nut holding the glovebox in place!