Electric confusion

my project is going very smoothly, fitted a 4.0 aj6 and getrag 290 into my 1990 auto 3.6.
all good so far.
however after trying to connect the engine harness im having an issue. after it goes through the firewall and to the ecu area(a manual xj40 ecu) the yellow socket doesnt fit with the xjs one.

is it a case of identifying what cable does what and splicing together? i’m useless with electrics…

It may be a little bit more complicated than that, but it might not.

I’d look at a wiring diagram for each car, identify the connector in each case and ascertain whether the colours do the same thing on each side of the plug.

It may be that they have different functions and if they do, then splicing them together is the last thing you want to do. For all you know, some functions are not available or new ones exist on either side of the looms or perhaps the pins simply need to be rearranged so that they mate properly.

It has always been easier to make things backwards compatible but there may be a very good reason why that isn’t so.

kind regards

Thankyou Marek. i’ll try and get my head around the wiring diagrams. they’re not my forte, and with mixing models of car into the mix, its a real big headache :-/