Quick update on my 85 XJ6. It came back from Coventry Cars recently with a rebuilt transmission. Now reverse works like a charm . All the gears shift up and down like they should.
Regarding my fuel problem, It turns out my right side fuel tank wasnt leaking, it was overflowing. They installed a new Changeover valve so now my right side tank works. BUT, it turns out my return valve wasnt working either. So I’m stuck using my right side tank until the new return valve arrives . My gas gauge reads zero (empty) at all times even though tank is full. I’m thinking it could be a bad connection behind the gauge? But I havnet checked it yet. It worked fine when the left side tank was activated(butten pushed in). Now that the button is pushed out, the gauge doesnt work. Any ideas on how to fix this? I could wait until I take it back to have the valve replaced, but Its scary not knowing how much fuel you have left I have to fill it up every day just to be sure.
Second issue, I just purchased a new engine wiring harness as all my harness look old and crusty. I also plan on changing the FI harness soon. I’m having trouble locating the engine harness. I see 2 big white connections with a bunch of smaller cables but I’m sure those are part of the FI harness. Does anyone have pictures of where the engine harness begins and ends?
Turns out, the switch wasnt connected all the way. I reached behind the center console/ dash and moved the connector around I tried pushing it in and heard a click sound indicating it is now connected all the way. The gauge works perfectly fine now. Thanks everyone for your reply
In fact, there is a fairly high chance that malfunction of our cars is caused by minor issues that are comparatively easy to rectify. Another source is minor issues that are a pain to identify or to rectify and the last, sometimes tragic cases are major issues really requiring an arm and a leg to get fixed …
Thank God - or whoever you prefer - that you just encountered the first type!
I tried looking behind aand under the battery and still cant find where the new harness is attached to… theres like 3 different box connectors attached behind the battery and I noticed therea space for a 4th one but it’s missing. Is there supposed to be free slot there? My new harness has a rounded connector and I’m not sure where that connects to?
That looks like a sub-harness connector for the forward engine wiring. Look at the RH side wall of the engine bay, down low, just forward of the front suspension area
As I recall, my 83 has a big hole just under the battery. The big harness passes through there.
A bit hard to deal with grommet makes the opening secure.
I tried looking again today. The harness connects to the ignition coil. It then travels towards the front of the engine where it separates into 2. One side goes directly downwards. Close to where Doug said. In front of the suspension, deep down is where that block connector is located. The other part of the harness goes around the front of the engine onto the left hand side where the remaining wires are connected.
I started removing and connecting the new harness but in the process I accidently disconnected this white and brown wire and did not see where exactly its connected to, so I’m stuck with an orphan wire. I tried looking through the forums but could not find it. I also got my book out and checked the wiring diagrams. I could not find a wire labeled WN for “white/brown”.
. All the gears shift up and down like they should.
. My gas gauge reads zero (empty) at all times even though tank is full. I’m thinking it could be a bad connection behind the gauge? But I havnet checked it yet. It worked fine when the left side tank was activated(butten pushed in). Now that the button is pushed out, the gauge doesnt work. Any ideas on how to fix this? I could wait until I take it back to have the valve replaced, but Its scary not knowing how much fuel you have left 
I have to fill it up every day just to be sure.
