yet another no crank - found cause but need help id'ing part
 

I have a 95 XJ6 that has had an intermittent no start (would start eventually) and seem to have found the problem bu not sure how to proceed. There is a large bright blue connector (switch?) with a bunch of wires running to it to the right of the j gate, if I jiggle it a bit or sometimes even just touch it it the car will crank. This happens when holding the key in the crank position so I'm confident this is where the problem lies. What I need to know is how to disassemble this and clean it without breaking it. So - can anyone tell me what this is/does and how to fix it. If a good cleaning doesn't work I'll check for breaks in the wires. Thanks. Note - I'm not talking about the park microswitch, this is mounted on the right/top of the j gate.

Hi nebigjohn,

See the diagram below from jaguarclassicparts.com, a great place to find exploded diagrams and part numbers, although in this case the diagram can be confusing. If the part you are describing is in the location of Part 29, then it's the transmission Decoder Module (DM). Later X300s have a Linear Switch in this location, and that's what is shown in the diagram, but late XJ40s and early X300s have the Decoder Module:


https://cimg6.ibsrv.net/gimg/www.jag...4ab371a103.jpg

Since your car is a '95 and has the same transmission as our '93, your DM may look like the one in our car and have the same part number, DBC10025. See the photos at the link below and the accompanying text, which explains its function and why a problem with it can cause a no-crank condition:

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I suspect you just have an intermittent connection but while you're in there, clean the center console ground stud, which is the ground path for the DM, J-Gate, Transmission Control Module (TCM) and several other components. Here's the method I use to clean ground studs:

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Let me know if this is not the component you are describing and I'll try to help.

Cheers,

Don

Thanks for the excellent info Don! I removed the connector as you described and found a fair amount of oxidation on the contacts. A little contact cleaner seems to have solved the problem (two days and counting). Also cleaned the grounds as you suggested and put a piece of electrical tape over the connector to help seal out moisture. It was a lucky find that the connector was causing the problem - never underestimate the value of poking at stuff with a pointed stick when theres a problem! Thanks again - John