Episode 1 of this saga focused on a mashed auto transmission selector, not broken transmission as advertsised . . . possibly because this car, at auction, was locked in park with non-functioning BPPS. For a detailed look at rebuilding the J-shift selector, with pictures, see this link . . .

<https://www.jaguarforums.com/forum/x...earbox-246896/>

With its shift selector fully repaired, park interlock solenoid tested, and a menagerie of other Cats to maintain, a year passed with this Jag driveable again, but BPPS still not releasing the interlock.

Episode 2 then followed . . . remove, test and repair the BPPS. The Joker himself was responsible for placing this BPPS in its most inaccessible location. Even after replacing driver's seat with soft cloths, a cross beam in the floorpan plays havoc with your back as you squirm to get your head up behind the dashboard. The downside to this approach is an inability to get arms up also, so you settle for arm and spanner room at the expense of a blind approach to the BPPS.

I know that the brake pedal's actuator arm is welded (not adjustable) and I cannot feel any other adjustment possibility. I simply cannot get my head in far enough to see, hence these phone pics. However, I'm certain how the BPPS, brake lights and transmission park interlock all work by operating BPPS manually once out of car. The following pictures illustrate the critical features . . .






The first pic shows the BPPS with upper slot that engages the body bracket at A and bolt hole for fixing at B to the body in the unseeable region shown in third pic. Note brake pedal bar at E that acts on C. The second pic shows the reverse of BPPS with ratchet mechanism C that rotates several degrees so cam changes over the twin micro-switches at D. It is this ratchet mechanism C that will fully compress in refitting unless the brake pedal is held fully depressed . . . thereby taking cam out of its working zone so that micro-switches never change state. Note the bolt, washer, locknut at B.

The third pic shows layout of the BPPS fixing locations (courtesy of 'hope and click' phone cam). With an assistant using long bar to depress brake pedal (careful of my nose!), the BPPS internal ratchet is fully extended, resited on pin A, bolted at B, and tightened with spanner on bolt head taped securely to side of brake pedal, and a second spanner engaging on locknut (grrr!).

Several critical elements are not shown . . .

• first, unlatch wiring connector (white in pics) which has a barbed retaining lug that must be depressed to allow plug and socket to part. What follows in R&R of BPPS is serious body contortion stuff, so you will need a partner, if only to depress brake pedal and extricate you;
  
• the pair of identical micro-switches are low cost parts that are readily purchased from any decent electronic parts store at less than AU$5 ea so, replace if their operation is doubtful, as you don't want to know the cost of an entire new BPPS;
  
• the pair of identical micro-switches operate in 'counter-mode' . . . ie one is wired normally open (NO) and the other is wired normally closed (NC) and NOT as shown on the wiring schematics . . . with both changing state on cam engagement by pressing the brake pedal;
  
• my solution involved flushing all areas of the cam, its ratchet and removed micro-switches with a liberal dose of WD40 penetrating oil, drying thoroughly, then lubricating the cam lobe and ratchet with good quality electro-lube;
  
• finally and most critically, the ratchet must be fully extended initially, maintained to the best of your ability during refitting by keeping the brake pedal full depressed, then allowed to reset as the brake pedal resumes (slowly) its normally off position.
  

What I found falls into several parts also . . .

• with deference to all dodgy backs, bruised foreheads and very blue language that flow from my approach, it could be that a more sensible approach is to lift the brake master cylinder, booster and pedal box out from engine bay . . . I am joking, but the thought persists;
  
• someone had been there before . . . I know this because once the BPPS was freed with brake pedal fully depressed, I found its cam ratchet fully compressed and thus, incapable of changing over the micro-switches;
  
• once fully checked on the bench, then refitted as above, the IGN-ON plus brake pedal was greeted with the sound of the transmission park-lock solenoid doing its thing. Eureka!
  
• sensibly, I decided to wait before reassembling more of the centre console and armrest bits as I figured it worthy of checking over a few coming weeks . . . would my fix be permanent?
  
• Alas NOT . . . some weeks later, but very next occasion I started the car, neither brake lights nor park-lock solenoid operated as intended. I was stuck in Park! Using the manual key-slot method, I moved the car. An hour later, when moving the car back into my shed, all brake lights sprang into life, as did the solenoid. Many months of go and no-go followed, usually accompanied by sleepless nights of wiring diagram nightmares and much hair-pulling!
  
• Clearly, something here was seriously amiss . . . and it took my son Tony to discover what it was, and how to fix it!
  

Tony's fix . . . owes much to his excitement of inheriting my early XJ-S to undertake its ground-up restoration. He was sympathetic to my disgusted frustration of this malfunctioning XJ-8 park-lock, my relegation of its 'ugly duckling' unloved status, and he proposed we revisit the problem. Almost immediately, and ignoring my request that he help me remove the driver's seat (again!), instead he attacked the rear fuse box . . .

. . . what he found there, leads directly into Episode 3 that will follow in a new companion thread, as it changes my thinking in regard to the (largely misunderstood) manner in which the electrics and electronics on most Jaguar vehicles (and others) of this era and beyond, are designed.