XK140 DHC Overdrive wiring

Hi All, Can anyone help me with an Idea of how the overdrive is wired in my XK140DHC.
It seems to have the earlier system as I have no Throttle switch or relays. I cannot find any wiring information for the overdrive anywhere. I wouldn’t mind knowing where the wiring runs as well. My car seems to have been rewired and I have a heavy wire going from the OD switch in the dash through a very rough hole that appears to have been punched through the bulkhead near the gearbox cover.
Thanks, Evan from Oz

As I recall, Rogers book called Jaguar XK 140 Explored has both overdrive wiring systems shown in his book.

I just rewired my 140 FHC and ended up relying on Roger’s 140 explored book for the wiring. I bought a new wiring loom, and the OD loom is an add-on, specific based on one or two relays/switches in your car (early or later but I don’t know the year. His diagrams are really useful as I found the colors used in the main loom matched all the wiring diagrams I could find, but the colors used in the OD looms varied quite a bit. Not difficult to decipher with the diagram, but not plug and play.

My car is LHD FHC with the single relay. From the dash switch the loom runs behind the dash and through the firewall into the fuse-box cover area with all the other wires. From there it runs down the firewall, into the right hand sill (alongside the rear lighting and fuel pump loom) and pops out of the sill about 2 feet down on the transmission side. From there it runs to the transmission switches and solenoid. The main loom has the reverse light switch wires, while the OD loom has the top-gear switch and solenoid wires.

It sounds like your wiring was a work-around… I bet they cut out the relay and instead ran a heavy wire direct from the switch to the solenoid on the left side…easier routing. Suspect your top-gear switch wire is probably still the original and runs through the sill.