1959 XK150S rewiring dilemma

I am rewiring my XK150 and have a dilemma concerning the overdrive relay.

There are 4 tags on the relay, C!, C2, W1 and W2. 5 on the wiring diagram C1, C2, C4, W1 and W2 - plus the wires on the new loom do not correspond. (2 slate/black on the diagram, 1 on the loom, plus 1 extra wire - slate /purple on the loom) the relay is original equipment and is still working well.

Any ideas would be welcome as I am not keen on that smell of insulation and fried components!

Thanks in anticipation - 3JagsPete

You got me stumped, So you need 4 wires, 2x slate and black , 1x slate , 1x slate and green,
My arithmetic tells me you have only 2 wires, correct.
I searched for a slate /purple and found one on a speed hold solenoid and travels to a speed hold selector switch. This tells me you have a harness for a BW automatic box,
150 3.4 3.8 Pos earth automatic.
You may want to check you loom package to see if its mislabeled or they actually sent you a BW loom.
Regards Morris.

Thanks for your reply, I realise now my initial inquiry is misleading. I only covered the problem wires.As well as the slate black and the slate purple there are also three slate green (2 into one tag and one single tag) plus one slate.

Assuming the 3 slate green go to one post on the relay, this leaves the slate, slate black and slate purple.

The relay is from a late Mk2 manual overdrive which I have just scrapped and by the state of the outer cover it had never been disturbed but I assumed it works OK. The original XK150 relay had been tampered with in the past, hence the replacement, it also has one less post - C1 (double post) C2 and W1, which throws up more problems.

The loom was made to order by Autosparks who are very good and took all particulars of my XK before constructing it, I assume it is as good as possible. Very confusing!

As you have probably realised I am no electrician and there is no guide from the old wiring as it was rewired in the past in red and green wires only, with plenty of twisted connections with insulation tape (a complete rats nest).

Any further ideas would be most welcome. Many thanks. 3JagsPete

You may not need the slate /purple as this was probably for the automatic.
The C4 and W2 get a slate /green [bunch together on the one W2 terminal I guess] seeing that you don’t have a C4. The other end goes to the o/d throttle switch, and then back to the dash switch as a slate and red.
W1 gets the slate /black which travels back to the dash o/d switch
C1 gets the other slate /black which goes to the overdrive solenoid.
C2 gets the slate, which also travels back to the o/d switch.

Can you trace where the other end of the slate purple goes, my diagram shows the ‘speed hold selector switch’ . I am not sure if this is on the steering column or accel pedal for the automatic, any how the roadster does not have one, so that’s why I say ignore it.
Many years ago I replaced my roadster harness and all went very well, I am not a sparky and all my advised should not be taken as gospel, auto electrics are my weakest point, however go cautiously with trial and error and be ready to disconnect.
Once you can get the solenoid to click you should be home free.

Many thanks, you have cheered me up no end. I will try this today.


Peter. Where are you , its still the 29th here on the west coast.

Could you pass on your eng number and Vin.