[J Type overdrive wiring]

If this has been asked before - apologies.

The overdrive has never worked on my 1974 MKIV Spitfire. Today I took the plunge and removed the gearbox tunnel. Does anyone have a wiring diagram the only one I have includes a relay. 
From the switch in the gear-lever one wires goes to earth. The other switch wire goes to the solenoid. A wire then goes to the gearbox isolator switch from the solenoid. There is an wire that comes from the engine bay (wired into the ballast resistor) which is attached to the gearbox isolator switch. Is this correct? 
please see pictures attached

Thanks Barry 

[Missing overdrive relay!!!]

Thanks Pete will try that for starters. Appreciate the advice 

Barry

[Missing overdrive relay!!!]

Hi All

thanks for your replies - yes it’s a J type OD - didn’t realise this didn’t need/have a relay (new to this).

Any advice re sorting OD would be appreciated.

Barry 

[Missing overdrive relay!!!]

Apologies if this has already been asked.

Overdrive on my recent purchase of MKIV Spitfire does not work. Before getting underneath thought I would check the obvious wiring to switch and relay. 
However unable to locate the relay which i understand should be beside the horn relay on the bulkhead. There is one wire labelled (with very faded masking tape) ‘overdrive’ which is attached to an in-line fuse and would appear to be wired into the ballast resistor. Please see photos.

All advice greatly appreciated 

Thanks

Barry