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Old 3rd July 2020, 18:00   #101
SD1too
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Originally Posted by xsport View Post
... have you double checked that 12v from the engine ecu is actually getting through at the pins ...
Yes we have Stefan, see post 79.

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Old 3rd July 2020, 18:13   #102
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... I used the master switch C0749-5 output ... Alas, instead of the IPK light coming on and cruise working as before, when I pressed the set/accelerate paddle, it flashed once and the horn sounded.
What you effectively did there Dougie was to connect the cruise ECU C0239-1 and C0239-8 pins together. I wonder if placing a diode between them would solve the problem?

You could use C0749-1 instead. That's the supply to the master switch but C0749-1 will be live only when the engine is running which is effectively the experimental state you have at the moment. However this might not work either because you'd then have C0895-8 and C0239-1 connected together!

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Old 3rd July 2020, 18:46   #103
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Yes we have Stefan, see post 79.

Simon
was the reading sufficient simon ? it all seams a little bewildering as to why it does not function.especially after changing of the interface as all the data requirements are there ... but are they in the right quantities ? or is something missing. have you ever known a kv6 180 sport auto without interlock ? there must have been a header in there at some point as dougie refers to a plug type fixing in there resembling a towing electrics plug affair. the header must have been removed unless a bespoke loom was made to order at assembly ... which i doubt very much. i cant see any towbar at the rear from the pictures and doubt if the interlock would have been removed for towing .. thats dangerous.! i wonder if the interlock circuit is incorporated with the cruise circuit at all. it may be possibly. what do you think simon ?

Last edited by xsport; 3rd July 2020 at 18:47.. Reason: i cant spell
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Old 3rd July 2020, 20:02   #104
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there must have been a header in there at some point as dougie refers to a plug type fixing in there resembling a towing electrics plug affair. the header must have been removed...
According to Rave, MGR discontinued fitting interlocks except for a few overseas markets. In these cases, a solenoid is fitted at the bottom of the gear lever which prevents the lever being moved from Park unless the ignition switch is in position 2 and the foot brake is applied. My car does have an interlock but it's not connected to the brake. I don't know what it actually brings to the party though. A header has definitely not been removed - the wiring loom is virginal. It's just not there because it was only used for cars with cruise, parking sensors and the brake application of the shift interlock fitted.

Incidentally, the mated headers in the engine bay resembling towing electrics plugs, are still only headers albeit different shapes to the normal oblong ones. The only connection of interest to the project has been the digital signal from the ECM to the cruise interface saying "ok, I'm configured for you" which was only partially fitted in the factory. I had to extend it from where it had been capped off to the cruise interface.

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i wonder if the interlock circuit is incorporated with the cruise circuit at all
According to the diagrams, it is connected (somewhere) to the auto transmission (C0932-43). The cruise interface also connects to that pin, but both are inputs to the EAT.

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have you double checked that 12v from the engine ecu is actually getting through at the pins
The signal from the engine ECM is a digital variable square-wave voltage between 0-12v. It's not a standard +12v supply. That signal is getting through (it's specified in post #79 above).
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Last edited by goltho; 3rd July 2020 at 20:19..
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Old 3rd July 2020, 20:12   #105
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What you effectively did there Dougie was to connect the cruise ECU C0239-1 and C0239-8 pins together. I wonder if placing a diode between them would solve the problem?
Yes, most likely. I'd thought of using a SPST relay triggered by C0749-5 and making a supply (maybe spliced from fuse 41 which supplies the entire cruise system) to C0239-1? Do you think it still might be susceptible though? A diode would certainly clean it up.

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Originally Posted by SD1too View Post
You could use C0749-1 instead. That's the supply to the master switch but C0749-1 will be live only when the engine is running which is effectively the experimental state you have at the moment. However this might not work either because you'd then have C0895-8 and C0239-1 connected together!
I didn't like the thought of a common connection there either.

Dougie.
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Old 3rd July 2020, 23:39   #106
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i wonder if the interlock circuit is incorporated with the cruise circuit at all. it may be possibly. what do you think simon ?
According to the wiring diagram there's no interconnection between the cruise control and the shift interlock ECU.
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Originally Posted by goltho View Post
My car does have an interlock but it's not connected to the brake.
My 75 is very early, built in May 1999, and there's no interlock either with the ignition switch or the brake pedal, so maybe I don't have the interlock ECU.

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Originally Posted by goltho View Post
I'd thought of using a SPST relay triggered by C0749-5 and making a supply (maybe spliced from fuse 41 which supplies the entire cruise system) to C0239-1? Do you think it still might be susceptible though?
Wouldn't that also connect C0895-8 to C0239-1 (which you've already tried when the master switch is closed)?

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Old 3rd July 2020, 23:58   #107
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My 75 is very early, built in May 1999, and there's no interlock either with the ignition switch or the brake pedal, so maybe I don't have the interlock ECU.
I'm sure the interlock has no bearing on the issue. I'm still not sure I have one - there's an ECU bolted to the bottom of the driver's side A pillar where they were fitted but I can't see what it is without removing it. I've no intention of doing so unless I have to!

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Originally Posted by SD1too View Post
Wouldn't that also connect C0895-8 to C0239-1 (which you've already tried when the master switch is closed)?
Well would it any more than using the experimental supply? I mean, everything ultimately is powered from the same source in the end. I obviously understand there is an issue with powering directly from the feed i.e. C0749-5 but I don't know the cause of it (do you?). My reasoning for the relay idea was that if C07490-5 was used only to activate the coil, it's such a low current that it shouldn't give a problem. The power source to C0239-1 activated through the relay can come from any suitable fused source.

My reasoning though is based on incomplete knowledge of what's causing the problem, so I can't know if that's feasible. A diode on the other hand is a one-way street and would provide the solution from the existing master switch. I guess I know which way I'm going. I have used Schottky diodes successfully before on projects. Their power drop is lower than standard diodes and they have faster switching speeds.

Dougie.
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• Built 11/10/2004 @10:22 hrs
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• Built 18/06/2002 @11:54 hrs: Registered 13/01/2003
• 4,906/18,894
• 206/813 Le Mans Green (HPD)

Last edited by goltho; 4th July 2020 at 00:06..
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