I have a real serious question and I hope somebody can help diagnose this issue. As you know you know if you havent seen my post, I have this 1984 v12 HE hand me down project car that does run but has temper promblems litterly, lol, I have found out from many of you this is normal and I should expect to maintain this child until...actually never it grows up. ha ha ha. Joking aside,
why has this car act normal on the start, drive it for miles on end, stop and start at many places during the day then all of a sudden...you turn the ignition key to start it, and it says, nothing. No noise, no clicking, no nothing for at least 20 plus minutes of turning the key. Mind you the battery is charged and radio works, what the HECK? Then after a long pause of praying and fasting *a joke* the engine turns and starts like it was running all along! This happen to the original owner for a long time and I asked the question, and did the shop say? Well you know the answer, they dont know. So inquiring minds want to know. Have you gentlemen experience any Alfred Hitchcock moments like this?
I hope you all have some ideas...

 

Yes, this happened on mine while I was working on it. In the trunk there are several ground wires near the ground point of the (-) side battery cable. The large, thick one goes straight to the body, then there are several smaller ones that mount nearby. They had some corrosion and would intermittently cause the symptoms you describe, so I cleaned them, sanded the contact point on the body and haven't had the problem since.

 

Many possibilities but Jamey's suggestion is a good one. Might as well clean/tighten the cable at the battery itself and, as long as you're in the mood, clean the "+" junction posts on the firewall as well. Loose/dirty/corroded connections are the #1 cause of electrical problems on these old Jags.

Cheers
DD

 

Mine has done the same thing since I have owned it. I suspect that mine is the ignition switch sometimes making contact and sometimes not. It doesn't happen every time I drive it but about half the time. I have to keep attempting to turn the key to get it to "catch" or make contact. It always does....so far. I am going to check the ground wires as the others suggested too. So far, it has almost never been the first suspect.

The electrical contact unit is attached to the key cylinder, unlike a lot of newer cars. When I get around to it, I will try to disassemble the contact part and clean it since cost new is around $160. Anyone have any experience with this?

 

I had similar issue, had to do with battery terminals. If you are losing battery connection while driving, it can also be dangerous to ECU, one unbalanced by battery power spike and we will be suggesting best place to shop for 16CU...

 

Common problem.

Lots of guys open up the switch and clean the contacts. It's been years for me so the details are foggy....but I recall it being intuitive.

The switch is held onto the cylinder with a tiny screw.

Cheers

DD

 

I agree with the ignition switch diagnosis also...

Dave

 

Whew, I thought it was a ghostly thing going on. I will inspect and clean. It would be bad to go on date night stuck in the car, but then again the passenger seat does go back. Thanks guys.

 

wait, I thought your car was SUPPOSED to either break down or run out of gas on a date?

 

I agre with Jamey.

Dont give the Jag a bad name and make it reliable HAHA.

Doug is correct on that "tiny screw", and it is small, and a mongrel to see and replace, getting it out is simpler, gravity takes care of that.

The switch is easily cleaned when seperated from the barrel. Spray some Brake clean or Carby clean inside and work it some, then follow up with RP7 or similar. Taking it apart is a CAREFUL approach, as it has springs and stuff inside that WILL fly off if you are careless. I usually open them inside a clear plastic bag (freezer bag is good), that way errant items stay in the bag.

The car will have ghosts, so be nice to them, usually by smiling whilst driving that awesome classic car is enough.

 

There is a ground point on the right/rear of the engine (Intake manifold) of the engine too.