Cruise control won't work.

[Bushbasher]

Ok, this is driving me nuts. The other day I was tracing an issue where the car wouldn't run on petrol which turned out to be one of the plugs having come adrift on the change over switch. To get to it I had to pull the fuse box out and I also went to the relay in the drivers foot well kick panel. While I was at it I also re-sealed the gas line from the converter to the mixer chasing a starting stutter, in doing so I had to disconnect the plug from the master cylinder pressure switch as the pipe elbow coming from the converter is nearly up against the plug which made it awkward to get the plug off......... so, when I fixed all the Fuel problems I put the car back together and everything was hunky dory ...till I went for a drive and discovered my CC was no longer working, it comes up on the dash when activated but won't engage, hmmm???. So I came back and proceeded to chase the problem thinking it had to be something I'd done while fixing the fuel issue. To shorten the story a bit, I'll tell you that since yesterday I've checked all the fuses and changed out the brake light globes, the brake pedal switch, the master cylinder pressure switch, the clock spring and the steering wheel buttons and still the CC won't engage. I've checked that there is power getting to the master cylinder pressure switch, thinking I'd broken one of the wires, and there's power there. I even got into the plug and bent the tabs back in a bit to make sure there was a good contact when plugged in. At this point, let me say that there are no other issues or dash lights or codes showing up and everything else is doing what it's supposed to. I'm completely baffled now and can't think what to try next so I'm hoping someone on here can help me out, is there anything I've missed?

Cheers
Bushbasher

[The Monty]

Edit: I should read posts before posting...

[auIILTD]

Hi Bushy. You really do need to consider paragaraphs. Very difficult to read. Sorry.

As soon as you mentioned the master cylinder switch, I thought you would be on to it. That switch is an override to disable CC when you apply the brake. I have had this issue on my on my NL Fairlane (same CC system).

You mention that you have voltage at the master cylinder switch. What about the other side of the switch? Is there a difference in voltage either side of the switch when you apply the brake? My bet seeing that you have played with that switch is that your problem is there. I hope.

Good luck. I hope you can get it sorted.

Stu

[Bushbasher]

Sorry Stu, I tend to ramble when I get started, next time I'll try to break it up a bit.

All I did to check the Pressure switch voltage was to unplug it and stick my multi meter probes in both sides of the plug and see if there was any power because I thought one of the wires might be broken.
It showed 12.58 on ignition and 14.5 with the engine running so I know it's getting plenty of power. When I put my foot on the brake the power spiked and fluctuated momentarily then settled back to it's original readings so I know the brake pedal switch is working too.
The actual pressure switch was changed for a known working one so I can't see how there would be an issue there but in the morning I'll go check the voltage while the plug is in and active. What voltages should I be looking for when the brake pedal is pushed?

Cheers
Bushbasher

[auIILTD]

All good Bushy. It is easy to Ramble - I do it all the time!

At this stage, I am not sure if the switch is normally open, normally closed or even has a resistive value. If you like, I will do some measurements on one of mine this afternoon and report back.

Cheers
Stu

[Bushbasher]

Ok, I don't know if I'm doing this right but with the plug plugged in it's showing just over 8v on both wires when I earth it out to the pressure switch. When I put the brakes on, the white wire drops to 0 but the red side stays at just over 8v, does that sound right?

[auIILTD]

Sounds about right for a normally closed switch, but I would earth to the battery or the block if your leads reach. When the brake is applied, voltage is cut from the white wire telling the ecu to cut cruise control. I will check mine and compare.

Stu