Where is the connection to ground originally located on the shielded wires shield?

 

What year model?

The shield wire should be grounded at ONE END ONLY and I would ground it to the ECU case. If it is grounded at both ends the shield will not do its job.

 

On a Lucas car, the shield itself is connected to the actual ground wire by a huge dob of solder just rearwards of the connector from the amp, in the engine bay.
The loom wire itself, just aft of the connector has a wrapped end, and if you unpick the wrapping carefully you will find the soldered connection to the shield.

 

Hi Greg, so does that mean on a Lucas car the shield is grounded at both ends?

On my car it is only grounded at the ECU end and the Marelli, where the wire is joined in the engine bay the shields are not connected, this is where the ignition module would have been in a Lucas car.

If the shield is grounded at both ends it will allow current to flow in the shield and then the shield does not do its job. A bad connection at One end will make this worse.

 

for the sake of tidiness I fitted the earth to the nearest inlet manifold bolt hole

 

No, the shield is only earthed at one end, as you say. I can't remember where the earth wire goes to, but I seem to remember it stays inside the loom outer. I'll go and take a look later.

 

On my 1996 harness the shielded ends are all spliced together and then are again spliced into one of the dedicated ground wires on my harness. That wire begins at one of the harness positions and ends at an eyelet just inside the engine bay.

I'm away from my records right now, but I can certainly dig them up if you want to see how they did it.

 

Sorry no signature on mobile I guess.
1986. Lucas.

I should explain why I'm asking.

"Shielded Wire"

The two-wire connection from dizzy to amp is a shielded connection as well. The shield is twisted up and crimped into a large eyelet connector. This eyelet is securely fixed under the rear-most amp mounting bolt. The wires are pulled through the shield close to their connection point.

That seems like a good strong, maintainable, testable connection. Nice!



The rectangular plastic plug that belongs in my amp has disintegrated. If you know where one of these can be found please let me know. Similar plugs can be found at parts stores in the US but are too large to fit.

"Notorious Shielded Wire"

The single, white ECU wire comes out of the amp, 5 cm to a black rectangular spade connector, 5 cm and into the shield. The shield appears to have been folded back into itself. It was then taped on the end. It appears to be original factory work.



It does not look like this end of the shield has ever been soldered.



This shield tests as grounded. But that ground connection is obviously not at this engine end. I assume that it is grounded at the ECU end, but short of cutting open the ECU bundle, I can't find the other end of the shield that is supposedly grounded.

The shield could be grounded properly at the ECU end. It could be shorted in between, It could be both.

I would rather ground it in the engine bay so that this is all easily testable and maintainable like the dizzy shielded wire, but I would rather not cut open the ECU wiring bundle to trace back from the pinout.

 

I'm surprised this hasn't come up more often. Mine has the same shielding. I've never seen this documented in any Jaguar diagrams.



According the the S57 book it's grounded at point "G6" which is described at "Trunk Right Side"

Cheers
DD

 

Yep leave it grounded at the amp.



No leave it grounded at the ECU end. G6 is next to the battery yes it's a PITA to get at but if you get in there and clean it up, and I mean sand the metal with fine sandpaper clean it with metho re-connect all the grounds then apply a marine terminal sealer or I used seam sealer, this will keep moisture out and the grounds in good condition.

If you ground it at the engine then there is another ground between the engine and car body. This ground is in a dirty environment and can be contaminated. NO sensors should be grounded in the engine bay, ALL grounds should go back to the ECU pc board and then the ECU is grounded.

A lot of the problems in the XJS are bad grounds, if Jaguar had taken ALL grounds to ONE point in the car most of these issues would not happen.


Probably an after thought when they had noise issues with the ignition.

 

Deleted my crossed wires.

 

I realise this has been cleared up by the electric experts; but IIRC, the earth wire is soldered onto the shield just where the loom wire goes thicker, just after the thinner part where the white wire disappears into the loom in the photo (usually the loom has a rubber collar on the thinner part). I think, repeat think, the earth wire then goes back to the boot as part of the huge bundle that runs along the car to the ECU.

 

I'll investigate the shield this morning and see if that's the case on my car.

 

Is it necessary? Where does the white wire connect? I tried to strip the large white wire to look for breaks and broke the shield. I see the black is ground run all the way to the rear. I need to find the end of the white to re-run.

Any help is appreciated. If shielding is required I my know a place to get it, just dont want to know the price

 

https://www.ebay.com/itm/Tubular-Bra...8AAOSw44BYWnX3

Couldn't you just use this around your wire, grounding one end?

 

I assume that probably would work. Do you have any idea where the other end of that wire ends up? I don't want to have to cut the hole harness open

 

The white wire or the one-sided ground sleeve?

 

The white wire goes from the Ignition amp (pre Marelli) to pin 18 of the ECU in the boot. On a Marelli car the white wire is joined at the LH intake manifold and goes to the Marelli ECU pin 24 and is grounded at the ECU end only. Any coax will do the job it MUST be shielded to keep noise out of the signal. The Fuel Injection ECU in the boot uses this signal to fire the injectors.