View Single Post
Old Nov 16th, 2018, 13:39   #8
Laird Scooby
Premier Member
 
Laird Scooby's Avatar
 

Last Online: Yesterday 20:24
Join Date: May 2012
Location: Lakenheath
Default

Quote:
Originally Posted by Rversteeg View Post
Changing the rear/brake lights for LED is not entirely without problems.
If you only exchange the two low rear/brake light bulbs for LED you will see the "bulb failure" warning come up every time you brake.
Quote:
Originally Posted by Laird Scooby View Post
If you go down the LED route Jim, don't forget to change the high level brake light bulb for an LED version as well. Duncan at Classic Car LEDs can supply a current/intensity matched red LED bulb for that as well.
That's why it was my first bit of advice Rob!

If he hasn't got cruise control then it won't matter if the LEDs aren't enough to give the virtual earth or short out the pull-up resistor in the CC ECU but the answer is simple if so.

Total wattage of all 3 brake bulbs = 63W so draws about 5A, therefore the resistance is ~2.4 Ohms.

As we now know this, using a 50W resistor of 3 Ohms as a dummy load will keep the cruise operating.

Take the feed to the dummy load resistor from the switched side of the brake light switch - it's before the Bulb Failure Module so won't effect the operation of that. You'd probably get away with something like a 10 or 12 Ohm resistor as a dummy load for the CC and be able to derate the power requirements of the dummy load resistor accordingly.

PS i've not encountered any ABS problems with LED brake lights on my 827s and they use the same Bosch system as the Volvos.
__________________
Cheers
Dave

Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........
Laird Scooby is offline   Reply With Quote