I am helping a freind that has a 1992 XJS 12 Convertible who took his car to a local mechanic because his original engine was overheating. The mechanic told hin that the block was cracked and he needed to replace the engine. The mechanic purchased a junkyard/used V12 and installed in the car. However the mechanic failed to identify the harness connectors( with tape/numbers/some notation) from the original engine and after installing the "new" engine told my freind that the "old" harness was not correct for the new engine and he couldn't
figure out how to connect the wires to start the car. I told my freind to have the car brought back to his house. I have purchased the CD for the car, printed out the wiring diagrams but want to know if there is a color coded schematic I can buy that will help the process. Also, I do not know for sure if the engine in the car now will even match the old wiring harness. Is there a engine I.D. pad on the V12 with a numerical number that will identify the year of the engine? At least I would know if the original harness is even compatable with the new engine. Any help is appreciated, this is a difficult task.

 

Welcome to the forum dgnaples,

I've moved your question from General Tech Help to XJS forum. Members here with the same model will be able to help.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some info about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

 

You need to start with the engine number located at the very rear of the 'V' where the bell housing attaches. gets grubby and hard to see but clean it up a bit and shine a light.
If the replacement engine is not Marelli ignition there will be a problem adapting as the motor will not have the front sensor mounting or the correct harmonic balancer. rear sensor mount is on flywheel cover so that would not be too much trouble.
Changing car looms and ECU's to suit earlier engine would be even more troublesome
If it turns out they are different I would not be very impressed with the mechanic dumping your friend in it like that.

 

Thank you for the reply, it is very helpful. And it is a shame that the mechanic didn't know enough to be more specific in his switch of engines or try to find out what he had before he bought a replacement. I will do my best. Thanks again for the direction.

 

I was told to find the engine id # on my freinds 1992 XJS12 convertible to determine the type of wiring harness that " belongs" to this engine ( see baxter response).

I looked today and found the following #8S84525SA.

If someone can assist with telling me if this engine requires the Merelli wiring harness or the Bosch wiring harness I would appreciate it. Thank you.

 

Hopefully Baxter can decipher the engine number

It isn't so much which harness is required (Marelli ignition versus Lucas ignition) it's whether or not you have a Marelli engine or a Lucas engine....for the reasons mentioned above.

If you have a non-Marelli engine (no crankshaft sensors) you'd have to figure out how to convert it to Marelli (install crank sensors) or convert it to Lucas ignition. Either way, it isn't just a matter of changing the wiring harness.

If it's a Marelli engine going into a Marelli car (which you have) let us know which wires are not matching up and we'll try to help.


Cheers
DD

 

According to my info marelli ignition was fitted from engine # 64245 and the prefix and suffix are xjs numbers so the replacement seems to be a marelli engine and should be a direct swap.
As Doug says, what and where do you have plugs or sockets not matching up?
If the looms are layed out in their logical positions and with all the different types of connectors Jaguar use most connections become almost self evident.
Are you able to post any pics?

 

dgpnaples,

As Baxtor has mentioned, that should be a Marelli engine. It's was built around the end of 1991 and being a 5.3, should be of standard configuration.

Good luck

Paul

 

I tried to post a photo of the harness but had no luck, not sure what the problem is. But I have a few photos of the engine as it sits in the car.