Kindly let me know which terminal (top or bottom post of the 80) shown in the attached photo of my 2008 XJ8 engine fuse box is the positive one. I need to attach the positive lead of a power charger so that my remote key fob can unlock the trunk. My car battery is completely dead as there is no power to anything in the car. As a result, none of the trunk power buttons inside the car or on the key fob work to open the trunk. I must replace my car battery. Both key fob batteries are fine. My second key is physically stuck in the trunk key hole. Pulling, pushing in and out, turning, and pushing down on trunk lid do not loosen the key. I researched our forum, the online owners manual, and service manual to no avail. If you can recommend a power charger for this purpose, I'd be grateful.

B

 

That's a fuse, so they're both positive. It's an 80-amp fuse, one side is directly connected to battery voltage, the other side feeds the circuit that the fuse powers. Use either post for your positive connection.

Since you can't get to your battery, you can't do a continuity check to see which post is between the battery and the fuse, and which post is "after" the fuse. Fortunately for you, that fuse is not on a circuit switched by the ignition switch, it's direct to the battery, so power there should power the car.

 

You can open the trunk with the key. There is a keyhole underneath the opening button of the trunk between the 2 lights for the license plate.
I also only found that when my battery was dead some years ago

 

Key is physically stuck in the keyhole underneath the trunk lid. No matter which way I turn, push or pull on it won’t come back out. It also won’t turn while pushing the release button on the left.

Is another option on this 2008 XJ8 to remove the license plate, drill a hole, and then push a long screwdriver through to release the trunk lid catch?

ISSUES RESOLVED:
I used a lithium ion power charger made by Fantik to power the in cabin trunk release. I followed your advice on hooking the positive to the engine, compartment fuse, and the negative to the frame. Wow was that a relief when the trunk popped open.

The key stuck in the trunk lid was resolved once I could see that the license plate frame and plastic cover would allow me to jiggle the key more if I removed those parts from the license plate. I will no longer use the license plate, cover and frame.

I really appreciate the quick responses and advice on this forum. Kudos to all respondents.

 

Oh, that looks really bad. Fortunately (for myself at least) I cannot answer the drilling-a-hole question.

Are there any cigarette lighters in the car that are on permanent live? The one in the ashtray switches with ignition, but maybe one of the rear ones is on permanent? That would be a good way to feed voltage into the system an easy way with available adapters contained with many chargers.

 

All of the cigarette lighter plugs are switched with car power. Wfoo's answer is a good one--all of the fuses are positive---so apply power with a probe (like with a multimeter probe) to either a fuse that is normally active, or pull a fuse and apply 12V power the same way. If you're wanting to hook up a jumper cable, unbolt and lift the fuse center out to attach a positive cable, then ground to engine or body. Alternately, if your back seat has a pass-through, reach back with a coat hanger and hook onto the emergency release.

Good luck!
Paul

 

Most good chargers should have a reverse voltage protection, my CTEK for example has.
So also wrong polarity should not do damage, just produce an error light on the charger.

Like paulz67 and wfooshee wrote, PLUS to one big fuse terminal and MINUS to the body should do the trick and repower the car. Charging current will certainly be below 80 A, so charging can be done with installed fuse in my opinion. Depending on the terminal it will charge through the fuse or pass by the fuse.

 

"ISSUES RESOLVED:
I used a lithium ion power charger made by Fantik to power the in cabin trunk release. I followed your advice on hooking the positive to the engine, compartment fuse, and the negative to the frame. Wow was that a relief when the trunk popped open."

I was also one of those theorising that powering the 80A fuse might allow trunk release. Thank you for actually testing it! (this is the first documented confirmation)

I also, once every year or two, see if the "key-in-the-lock" trick still works, since that lock is seldom used if ever.