Hello everyone. I've got another XJ that I'm bringing out of hibernation and am starting a thread so I have a cohesive place from which to ask questions of the collective wisdom of the Jaguar Forums. Thanks in advance for your always helpful and often entertaining support!
The car is a 1978 XJ12L, USA market, Sable over Biscuit (I think). Fairly late in the series 2 production. Bought new in Minnesota, USA, for $18,700, then brought out here to Washington. One owner before me. It now shows 39,000 miles with evidence to support - the owner (father of a colleague of mine) had a variety of collectable cars, including an XJS with even fewer miles. Usual story: used, parked, refurbed, used a little, parked, refurbed, used hardly at all, parked... and then me.
It starts and runs, on some number of cylinders probably between 8 and 12, and the brakes and cooling all seem fine. The transmission (TH400 of course) is a big oily question mark. A ton of work was done to this car during prior refurbishments (yes, including fuel tanks, pump, filter, etc., not long ago). Optimistic Me thinks this one is going to need even less than the prior XJ6 adventure I posted about. I've had a V12 XKE before, so am pretty comfortable with the engine, and the rest is obviously similar to the earlier XJ.
But I'm bound to need some help! So thanks for being here, everyone.
I'm slowly working my way through this newly acquired 1978 XJ12, cleaning and assessing, checking and renewing fluids, testing various systems.
One of the first things I want to fix is the tachometer. The car was converted to a modern electronic ignition a few years ago by a shop tasked with getting it running after 10 years of hibernation. They went with the FAST (nee Crane) XR-700 unit. I would rather the car was original and I could do the re-OPUS conversion, as that worked well for me on the XKE. But the XR-700 is fine, happy to use it.
I gather the tach hasn't worked since it was installed. Right now, the ballast resistor has been bypassed, with the tach wire going direct to the coil. The car runs, but the tach doesn't read. If I wire the tach through the ballast resistor like it is supposed to be (both factory and specified in the XR700 instructions), the car doesn't run. What I think I need, then, is the diode wire noted in the XR700 instructions between the coil and the ballast resistor, instead of the straight wire. The XR700 kit should have included one but it is missing. I guess I will get a diode and make one up.
I can't imagine the tach's current "draw" (negative draw?) is going to much more than a few watts? I'm thinking a 2 amp diode would probably be more than enough, and a 5 amp diode massive overkill.
I always thought that colour was Carriage Brown, but I may be wrong. The low mileage is quite incredible, and the car looks to be very well looked after, so I hope your high hopes pan out.
Carl, thanks for the note. Yes, absolutely, tach wire is going to the negative side of the coil. And, after making up a diode wire, it didn't fix my issue so maybe the tach is broken or maybe there's a wiring issue behind the dash (oh the horror!).
Fraser, my mistake, I refer to Sable out of habit from past experience, but you're absolutely right that this is Carriage Brown.
The car is cleaning up very well and no bad surprises (yet). Need to take a few days and address a couple of clogged fuel injectors, and then I'll have a better sense.
