OK Graham, I'm "working from home" today (and it looks like rain in Scotland) so had another chance to get out and get under, and now I need your advice again please. Remember, no electrical skill, just a fused jump-wire and a test light, certainly nothing with numbers or other displays!
Test light attached to red wire and touching earth, light comes on!
Jump red wire to Black+Yellow, fan starts (good) and test light now goes OUT
Therefore presumably this Otter is an earth switch, but I'm out of my depth already
So if I want just to switch the fan on manually, I bring a wire from each of the otter terminals up to the new switch and Bingo!
But how can I add a warning light at the switch end? Presumably it will need an independent, fused power feed, permanently on, then I link in the earth from the switch - does that make sense? Presumably I fit the warning-light earth onto the earth (BY) side of the otter, rather tha the red, otherwise I would have HOT wires on both sides of the warning laigh - told you I was getting confused!
And now, if the fan is switched on manually, what happens if the Otter is open too?
There is what appears to be a wiring diagram on the GoMog site but the wire colours don't fit as show BY into otter and B out, whereas I seem to have R in and BY out, see http://www.gomog.com/allmorgan/wiring88&89.gif
many thanks in nervous anticipation
John

Interesting. Your wire colours do not appear to match your wiring. You can as you suggest jump the otter switch. Wiring a warning light is now more complicated, but you have the right idea.

I don't suppose you can see the wires where they enter the fan motor?

Cheers,
Graham

yes I casn see them going into the fan Graham, but they both look black! Any guidance on which side to fit the warning light?
thanks, nervously, John

Now traced back further to bullet-junctions, and the answer is ...
one Purple, t'other, Black & Yellow going into fan, which is consistent with the wiring diagram on GoMog site
Any chance this is just another Morgan anomaly?
bw - John

Hehe,

Sorry. You need 'hot' wires both sides of the warning lamp - that way it will be off when the switch is off and on when the switch is on. However, it will also come on when the otter switch switches on (just as my Kenlowe does).

So, fused supply to lamp (small fuse if it's only protecting a lamp or LED). Other side of lamp to 'red' of otter switch (or its extension lead to the switch on your dashboard).

Both wires into your fan are black? Not one being black/yellow?

Have to admit, I'd rather do this myself, than at a distance! Any JockMog members near you with some electrical experience?

Cheers,

If you look in the Demontweeks catalogue (page 251 - Part No. sw4005)£8.50 - Illuminated Fan switch. You can get a rocker switch in the correct style to match what you already have and will give you the inputs requried to install.

Have Fun

Thanks Graham, red on red then! If you look at my second reply earlier thisd morning you will see that I found the wires into the fan unit itself are (just like the diagram) Purple and Black&Yellow
As for switches, I want to put a waterproof switch on RH side, at bottome of dash panel so well away from knees, and Vehicle Wiring Products can pair that up with a round amber light c/w Fan symbol!!
Now I need to add an in-line fuse holder to my list and I think I'm almost there ...
Working from home is so productive, I always find - anyone for tennis?
regards all - John

Latest development - plan A didn't quite work as I could either get warning light OR fan on, but not both. So now reverting to a 2-pole switch with entirely separate 12v feed & earth circuit for warning lamp. Watch this space

Hmm, sounds like there is a relay in there then.

Isolating the warning/indication circuit is a good idea anyway.

Cheers,
Graham
(Just back from Snowdonia - by Z3 unfortunately - SWMBO worried about the rain!)