Weird indicator and brake light issue

I have a land rover 90 with a 3.5 litre v8 conversion. I have a weird issue with the indicators and brake lights. when I turn the ignition on the indicators, brake lights, and windscreen wipers all work as intended, however when I turn the engine they do not work. I've tried swapping out some of the fuses but to no avail.
any idea or suggestion would be greatly appreciated.
Thanks

You have a classic earth fault - do a search on here for same - been done to death..

Essentially, a major earth is either crusty / broken / missing / disconnected - it's a LR, it is sort of "normal"

" when i turn the engine they do not work" Do they work once the engine is running?

tottot said:

" when i turn the engine they do not work" Do they work once the engine is running?

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No they stop working once the engine is running

Then as above, faulty earth. There is an earth point to the right of the brake servo on the bulkhead.
Thing is if earth points are not working the electrickity can try to find other ways back to the negative of the batt. Can go along other items like speedo cable or even hand brake .

tottot said:

or even hand brake .

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+1.

OP:- the above is a well known, and quite frankly somewhat scary issue on the D1 - cable becomes earth lead - is NOT us to the job - gets hot, then is no longer tempered - therefore is no longer a cable - therefore snaps .... you can guess the rest!

So, if you have a HB or Speedo cable, I'd be looking sooner rather than later!