Hi there, recently purchased a 98 xjr and have conquered all the quirks that were handed down to me except one. i have the harmon kardon system with the 6 disc changer. The headunit will turn on only when the parking lamps or headlights are turned on, it does not work when the knob is fully advanced in the auto position. The headunit fuse in the left foot well was not present when i received the car and replacing it made no difference. At this rate i am assuming a previous owner wired it into the parking lights some how? I would like to avoid tearing out the stereo because i will probably just wire up a whole new system if i get there (did it in a vw corrado years ago with the individually amplified speaker system, running wires wasn't fun). So, basically i'm wondering if anybody has input or suggestions to save me some time, because i really just want this stereo to work the way it is..... with the headlights and parking lamps off thanks

 

There's no quick or easy way to find the cause of electrical problems like these, unfortunately. You'll need to get the wiring diagrams from the JTIS (available as a download from this site) & locate the main power feed wire to the head unit. Use a multimeter to check when the supply voltage is 'live'.

If it follows the same pattern of the lighting switch positions you mentioned, then you have 2 options:

1) Completely trace where the feed wire goes to & then re-wire it correctly.

2) A shorter method is to cut the feed wire, insulate the dangling end that comes from the lighting switch to avoid short circuits, and then connect the other end from the head unit to the ignition switch.

Electrical faults are bad enough without having to trace & undo other people's bodging & rewiring jobs...

 

As you stated, "Electrical faults are bad enough without having to trace & undo other people's bodging & rewiring jobs..." rewiring a whole new system will be worth it in the end

 

I've had all sorts of electrical problems over the years in various cars where other people have been messing around with the vehicle's original wiring-usually to install alarms, immobilisers, or uprated sound systems.

Nasty clumps of wires all taped up & shoved anywhere convenient, scotchlok connectors on everything, spliced-in solder joints that were intermittently dry & failed every now & then.

I usually unpick all the bodged wiring, remove any scotchlok connectors & then remake all the joints with solder & sleeve them with heatshrink tubing-then I tape-up the loom so it all looks neat with reliable joints that have a consistently low electrical resistance.

It's a long job but worth it in the end...