Jump to content

Brake lights on continuously, RRC 1992 with Wabco power brakes


LiftedDisco

Recommended Posts

I’m using the running gear etc from a very rotten, very scrap 1992 RRC which includes re-use of the Wabco power brake system.

Everything has been bled through and working… hell’s teeth and hallelujah, or so I thought…

I now have a weird issue - ignition on and the brake lights are on continuously.  This seems to be a new thing as the system was all working OK when I’d originally bled the system and the ABS lights on the dash were going out when road tested.  Brakes are pumped up, and working.

I’ve checked brake fluid level, all OK and have changed the brake switch for a new one which hasn’t made any difference.  Fuses appear to be OK.

Has anyone come across a similar issue - I’ve been through the fault-finding pages and all the errors appear to relate to lights on the dash rather than the rear brake lights being on - I do appear to have a permanent live at the trigger for the brake light relay, so suspect it’s in the ‘control’ side of things…

Anyone got any thoughts or inspiration…?

 

Many thanks!

Link to comment
Share on other sites

Assuming it's this type: http://graphicvillage.org/meritor/MM0401.pdf

The pedal switch isn't a simple switch - two resistors, one of which is bridged when you press the pedal.  It would be worth checking with a meter that the new (or old) switch gives values close to 27680R when released & 680R when pressed.

It's possible that over the 30 years, the resistor values have drifted out of the range the controller will accept as OK.

 

image.png.450460919b5ca1646673da21720f8f8d.png

If the switch is OK, try some random resistors between terminal 1 & 2 on the controller, with the switch unplugged.  It could be that the resistor inside the controller, it's using to compare the switch value against has drifted.  It may be that by plugging in different resistor values, it will work again?

 

Link to comment
Share on other sites

Are you sure the switch is fully seated and the pedal is pushing it in far enough? You can try removing it or plugging the old switch in again and testing it by hand without mounting it on the pedal box.

The brake switch has 2 sets of contacts inside: one normally open that is closed when applying the brakes, like in most brake light switches. Standard wiring is GP and WP. The other set of contacts is for the signal to the ABS control unit, WS and GK.

Link to comment
Share on other sites

OK… confession time…

 

Given that I’d removed it all from the RRC some time ago and am now knitting this lot into a bespoke loom that includes classic RRC display, D2 dash and switches and a home-spun loom for lights etc and ancillaries, it’s come as now real surprise that I’d managed to drop the ball when connecting things together…

 

Now traced and resolved!

  • Like 3
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy