My 1984 HE had almost no action in the instrument panel, so I decided to insert an extra ground cable and clean the contacts (courtesy xjsonabudget.wordpress.com - thanks!)
Before this, it had been necessary to take off one battery lead when parked for more than a night, due to power drain, even killing the battery.
I have installed a new and fresh battery, and when going about to reinstall the instrument panel, I decided to have an extra go at checking for the cause of the power drain. All fuses out, and now there is an electric arc when I try to put on the second battery lead.
I haven't fooled around with any other cables and connections. My suspicion is that an unfused component has faulted - coincidentally - while the instrument panel repair process has taken place (I must admit it has taken some time due to travels and work).
Now I measure 746 ohm over the + and - cables with the battery unconnected and all fuses out (well, not all really, because of the widespread 6-something inline fuses), and upon trying to connect the battery, the second cable causes an arc upon trying to connect it. A constant load of 746 ohm shouldn't by itself draw that much current to cause an arc (only some 17 mA), so it is probably some more advanced circuitry.

It this consistent with alternator or regulator failure? Or starter failure? Any other hints?

Hopefully,
Thomas

 

Thomas,

Firstly, welcome to the Forum.

Just because I can say it, is the battery being connected the correct way around, coz the wrong way will give that arc, for sure.

THEN:

My first suggestion would be to remove that "extra earth" cable, just to get back to basics.

An arc as you describe is serious. Any BROWN wire in that car is +ve HOT, and may be the issue, but of course, which one.

An alternator would certainly do that arc, as I have had that numerous times. Unplug the solid Brown wires at the alternator, insulate them, and try again.

On each side of the engine bay, at the rear, are the 2 +ve connectors. The battery +ve cable comes up under the car, and connects at the LH connector, then another solid cable traverses the rear firewall, to the same type of connector on the RH side. Another cable from there goes to the starter motor solenoid. There are smaller wires on those connectors also, dependent on market requirements. ANY of these could be shorting the system serious enough for that arc.

After that, is is simply ONE wire at a time until it is found, FUN.

 

Thanks, Grant!
I'll go looking!
By the way, I'm pretty sure that the extra ground for the instrument panel is not the culprit - the same behaviour occurs when the panel is out of the car (and the multi-contacts for the panel are not touching ground themselves).
Rgds, Thomas

 

My vote, if I have one, is with Grant. Indeed, it is a substantial drain, just short of a complete short to ground.


Eliminating all fuses, isolates the issue to an unfused circuit. Brown is the Jag color.
I would start as Grant opines, with the alternator. disconnect and check and see if there is a current from the _- post to ground.


One step at a time, though. More than one fails to isolate the fault




Carl.

 

or....


use that wonderful meter to find out which on the brown wires has 746 ohms to ground...


might be quicker....

 

Erhmmm...
Turns out that Grant was right with his initial comment: The battery was indeed tried connected wrongly. (To my excuse - it was a new battery with less than obvious markings, and I put it into the battery mount "on autopilot")

Thanks to Grant, JagCad and Jonathan for advice! I'll be more cautious hereafter...

Rgds,
Thomas

 

Drinks on you.

A very lucky find, but I would still be checking that alternator, it may already be damaged. They are NOT forgiving, even for a millisecond.

 

YES, that is why I have thrown out all my jumper cables...


cost me an alt. one time... that was enough for me...


Jonathan

 

You are lucky that your fuel tank wasn't leaking otherwise they would have been picking bits of you off the nearest glacier.
I did a similar thing as a newbie and cross connected a bank of 4 24v batteries in a radio station; blew me out of the door.
Luckily the acid went up as I went out and I managed to preserve my good looks; 40 years later it's hard to tell the difference!
A valuable lesson though and one that has never been forgotten.