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Topic: Starter Inhibitor switch - location? (Read 693 times) |
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carltailfin
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Starter Inhibitor switch - location?
« on: Jul 8th, 2025, 8:15am » |
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Ongoing problem with my Scorpio. Only turns over on the key when it feels like it. Have tested earth connecter in main fuse box for inhibitor relay - this sometimes gives earth - but mostly not. I am now suspecting the inhibiter switch itself - does anyone know where this is?
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brds
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Re: Starter Inhibitor switch - location?
« Reply #1 on: Jul 8th, 2025, 8:30am » |
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The relay is the inhibitor switch. It receives earth from the Transmission Range Sensor to operate the relay (ref. diagram 26-01-05).
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #2 on: Jul 8th, 2025, 9:50am » |
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Hi brds. OK - so could the transmission range sensor be at fault? I have been led a merry dance by testing with the multimeter this morning. Testing from connector 85 in the main fuse box I was getting no earth continuity to the bodywork - then it changed its mind and gave me continuity - hurray! - but with the transmission selector in any position from park to drive and everything in between! Boo! Connected up the relay via wires to fuse connectors 85 and 86 and it operated - again but in all transmission ranges........ Now it has gone back to giving me no earth continuity in any transmission position and of course the relay does not work again double boo! I have tried disconnecting and re-connecting the battery - and even - much to my chagrin carved out a small piece of extra plastic around connector hole 85 in the fuse box to check the condition of the brass contacts and ensure the bridging wire has good contact. Is the range sensor in the gubbins on the side of the gearbox under the car do you know? Is it a discreet part or part of a whole other assembly? I am coming to the conclusion I might have to take half the car apart again - dashboard out etc just to trace the wire to find where the break in earth continuity is between the range sensor and the main fusebox............not a great feeling.........! Have you any suggestions?
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #3 on: Jul 8th, 2025, 10:02am » |
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Wwondering if I can locate the earth feedwire from the transmision sensor in the multiplug located in the engine bay to see if it is giving earth there - or not......
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #4 on: Jul 8th, 2025, 10:16am » |
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Looking at the Scorpio wiring book I cant work out if 26-01-05 is for my build date a sit says nothing unlike most of the other pages relating to the starting system. However if it does apply to my '94 build date it shows - I think - that the earth goes through PATS first......... Could I have a PATS issue?
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brds
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Re: Starter Inhibitor switch - location?
« Reply #5 on: Jul 8th, 2025, 1:02pm » |
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You could check for earth at the engine bay multiplug but there are various connector options. What model car is it?
Also, the loom from the multiplug to the gearbox connector will almost certainly be a mess if you haven't rewired it.
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #6 on: Jul 8th, 2025, 2:07pm » |
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Hi brds. It is a '94 build date 2.0 litre 16v automatic Ultima saloon. The gearbox loom is completely new - I rebuilt the whole thing with all new wires about a year ago. It worked with no problems. I took the car off the road in December due to a VSS problem which led me to rewire a great deal of the rest of the car - most in the engine bay and in to the auxillary fuse box and A pillar, many behind the dashboard too. I dismantled both fuse boxes carefully and cleaned all the brass tracks - had to make some silver-solder repairs on some pins in the auxilliary fuse box. Main fuse box was in much better order. Each wire was replaced one at a time, soldered, heat shrunk and liquid-tape insulated. All multiplugs have been cleaned and treated with Ford dialectric grease. The whole job took 7 months around work etc. It is tempting to think I must have messed up somewhere in the re-wire - somehow - but I was extremely careful and also except to say when I first tried the car after the rewire it started first time and everything worked! Then for no apparant reason a day later this new fault of not starting happened - and seems to have taken permanent residence! After rebuilding the whole dashboard etc back in to the car, it continued to turn over - until it didnt! I really could do with knowing which wire going in to the main fuse box connects ultimately to terminal 85 so I can check its continuity and work backward from there - although I fear it might end up in a computer module befor ethe issue can be found leaving simple multimeter testing useless. Just dont understand why it worked the minute improved the relay connection to terminal 85 - and continued to work repeatedly until I took it for a shor tdrive last night whereupon the problem came back - and no amount of trying to test for continuity with a piece of wire from 85 to earth with a multimeter is coming up with the positive result I had on Sunday. In key position 2 and 3 the earth feed to 85 remains dead. I am tempted to wire a cheat switch to 85 and have done - but that is not really my way and wont make me happy - I really want to find the cause........I have managed to locate the range sensor on a spare transmission and take it apart for clues - but no joy...... Its actually baffling - although there is a system of arced tracks and sprin-loaded wipers it is impossible to see how a connection between 2 terminal pins can be made with the switch in the park position - multimeter continuity testing doesn't seem to work here - visual inspection hasn't helped either - its a blinkin mystery! Feeling bloody cross, perplexed, frustrated - hopeful, determined....... but also seriously running out of time! Still dont really want to fit a cheat switch......dont want to do Bernard Cribbens either! Right said Fred........
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #7 on: Jul 8th, 2025, 2:43pm » |
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Have read PATS will stop the engine from cranking if it doesnt get the right code from the key - could this be a reason why no earth at 85? Men in with the straight jackets will be coming soon! C arl
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #8 on: Jul 8th, 2025, 5:06pm » |
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OK.........Stop press...........are you ready for this...........have installed a bypass earth wire direct to pin 85 of the inhibitor relay........tried the key without earthing the bypass wire.........didnt crank over. Tried it by earthing the bypass wire - it started - quelle surpris! BUT then tried it again normally without the bypass wire.......IT STARTED! Tried it many times after that without the bypass - it started! then......tried it again - it didnt crank, bypassed it again - it cranked and started, tried it then without the bypass wire a few times and it cranked andstarted each time normally............can anyone shed any light on this gremlin behaviour? Its almost like forcing an earth to the relay is resetting something to work as intended - could this even be possible? I'm flumoxed!
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brds
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Re: Starter Inhibitor switch - location?
« Reply #9 on: Jul 8th, 2025, 5:52pm » |
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As the fault is intermittent it's probably just a dodgy relay coil or protection resistor/diode. Can only suggest you try finding one and change it before you go any further.
You're getting closer - Bob.
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #10 on: Jul 9th, 2025, 10:53am » |
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Hi Bob, thanks for staying with me on this. After repeated testing with different relays this is the latest after fitting a bypass earth feed wire to leg 85 of the inhibitor relay:
1) Extra earth wire to pin 85 enables car to crank and start no problem
2) After being used once, relay does not need extra earth feed - car seems to be providing it itself as normal - until......
3) Once the car is driven, the engine will not crank again unless earth bypass wire is used but WILL restart providing its own earth feed to pin 85 after that - until it is driven again..........repeat cycle above!
How weird is that?!
Carl
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brds
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Re: Starter Inhibitor switch - location?
« Reply #11 on: Jul 9th, 2025, 12:18pm » |
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Do the relays you are trying have the same coil & contact pins?
What is the coil resistance?
You could try warming-up all the soldered connections on your relay - it may be just a dodgy joint.
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #12 on: Jul 9th, 2025, 1:05pm » |
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Hi Bob,
Yes they are all the same. I don't think it is the relays though because I have tested the fuse box connection 85 itself with a multimeter (relay removed) and sure enough, the car does not provide an earth except in the circumstances described in my previous message. The car does however, provide 12v live feed at all times when the key is in the appropriate position - as tested by the multimeter. For some reason the car is withholding an earth feed to 85 after it has been driven - but provides it again if I short the 85 connection to earth just once............ It's weird! No doubt the cause - if found - will turn out to be really simple and obvious in retrospect - but for now, I'm comfounded! Carl
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brds
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Re: Starter Inhibitor switch - location?
« Reply #13 on: Jul 10th, 2025, 8:53am » |
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I'm not an expert on PATS but it looks like it's not happy to give an earth permission after being driven. What happens if you lock & unlock the car?
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carltailfin
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Re: Starter Inhibitor switch - location?
« Reply #14 on: Jul 10th, 2025, 11:28am » |
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Hi Bob. Yes I was wondering that.........Key fob works no problem and activates PATS with the correct flashing light on the dash. The issue still remains after locking and unlocking though........
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