Wired battery up the wrong way !±!

Hi. Could really do with a bit of help here I have exausted my limited amount of knowledge.
1994 XJ40 ( Batterey in the boot)
I Had a flat batterey but always have a spare charged one in the boot. Not having my glasses on i jumped the flat battery with the charged one, unawhere that the terminals were round the wrong way.
Ignition lights came on and then went off after turning the ignition key to start.
Realising my mistake and kicking myself i started going through all the fuses…Fine
I then started delving a little deeper, discovered a relay under the gearbox consol which when bypassed seemed to eleviate the problem as thge ignition lights came on again !!
Tried swapping the relay for a new one (Twice) but no joy
I have been informed that i have probably buggered the ECU, Alternater and possably the coil also and the car is junked
Really do not want to scrap it, as its only done 59,000 miles and two owners from new I Love it and do’t mind spending a bit to get it on the road
Anyone out there that could give me some advice ?

Quote Reply

What are those strange links?

Sorry …
Strange links?

There is a “reply” and “quote” in blue on your post that implies you are trying to link to another page. You can use the pen icon bottom right of you original post to remove them.
As far as the reverse polarity, yep I would say (from first hand experience) you are looking at the least for a replacement ECU.

With the battery connected **Correctly **do you have lights? They should not be affected by reverse polarity, nor will any electric motors.
Previous owner of my XJ-S did the same as you; blew out the diodes in the alternator but did not harm the ECM ( don’t know if he turned key on).
If you have no lights, you may have blown a fusible link. Don’t know if the XJ40 has one, but if it does will be between the battery positive and anything fed direct battery power, such as ignition switch and fuse boxes.

Thanks Robert I will check out and keep you guys informed. Appreciate the help !!

Looks like OP cut and pasted post from another forum and that forum included back links to the original post

why did you need to carry around an extra battery in the first place… have you been having problems… dangerous

I Don’t carry an extra battery around It is just in the boot (trunk) whilst parked in my drive as the jag is only used very occasionally.

In my opinion, unless you keep a modern Jaguar on a battery maintainer using it only occasionally is a recipe for problems.