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Discussion Starter #1
83’ Silver Spirit. Starts and run excellent with brake light functioning . When i I turn it off after a while and start again - uneven run on 6-7 cylinders and the brake light doesn’t work.
I’ve tried different things.My guess is a bad connection that heatens up creating the trouble. My guess is at the starter key because the brake light doesn’t work and the uneven run (low voltage?). But before dismantling everything i world like to ask if :
—— anyone experienced the same or have any suggestions on the fault ?

kind regards
 

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The word "brake light" with reference to RR can cover a few areas.
Is it the actual bulb in the tail lamp?
Brake pressure lamp?
Parking brake lamp?
 

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Discussion Starter #3
It‘s the bulbs in the rear brakelight. I wonder if it could be an earth connection that is bad. Or something in the house of the starter-key.
 

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Discussion Starter #4
The uneven run of the engine is always connected to the missing rear brakelight
 

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Could be the key, but I'd say it's more likely a bad ground somewhere. What happens if you turn the headlights on?
 

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Could be the key, but I'd say it's more likely a bad ground somewhere. What happens if you turn the headlights on?
Works ok.

All your answers and suggestions is most appreciated. An electrical fault in a RR is a nut to crack 🤗
 

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A fellow Dane!

I'm not sure the ignition switch has an influence on the brake lights. Do they normally light up when they brakes are applied with the switch off?

Es
 

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If you just bought the car, start with washing with connector cleaner all fuses and relay sockets and easy available connectors. Check&replace fuses to desired amperage. By the way you should eliminate all noticed loosen/burned out contacts or tearing off wires. Made any diagnostic before that actions is IMHO a nonsense.
 

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I'm not sure the ignition switch has an influence on the brake lights. Do they normally light up when they brakes are applied with the switch off?
There is something like "stop lamps failure relay" that will be sensitive to voltage level at cars circuit. Anyway, take attention, that stop lamps consume a lot of power (4x21W). As the engine run roughly, there could be no power for diagnostic lamps too. I believe "stop lamps" problem is a result, not a cause.
 

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Discussion Starter #11
Thank you for all the comments. 🤗
The car runs perfectly at the beginning, everything functioning even the brakelights. If i turn it of and then start again, the motor runs uneven, not on all cylinders and the brakelight bulbs fail.
Could be low voltage in some part of the car (the meter say’s 14 v in the instruments) and the “stop lamp failure relay” Fall out As a result of that low voltage. ?
 

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Thank you for all the comments. 🤗
The car runs perfectly at the beginning, everything functioning even the brakelights. If i turn it of and then start again, the motor runs uneven, not on all cylinders and the brakelight bulbs fail.
Could be low voltage in some part of the car (the meter say’s 14 v in the instruments) and the “stop lamp failure relay” Fall out As a result of that low voltage. ?
“Stop lamp failure relay” will turn on the "brake light" alarm lamp on dashboard if any of four bulbs in brake lights will be burned out or will be "no contact" in its circuit. It should not turn-off brake lights itself, but it is the only ECU in their circuit. Anyway, in powering up brake lights are involved 2 or 3 fuses and some other relays...

1. What do you do to return the car to working state? Just turn engine off with a key and wait something like half of hour?
2. When the car is in "bad" state, what is not working except stop lights? Beams/headlights/blinkers? Radio? A/C? Windows/Seats? etc.
3. Is it always needed to turn off/on engine to set "bad state" or the car will go into it self after some time of engine work (like half of hour)?
4. What you exactly test/check before? Did you try just to full load or replace a battery?

AND

5. What you mean with the word "brakelight" - brake lights in rear lamps OR "third" brake light in the middle of rear window (if mounted).
6. Is it a car with carburetor or injection?
 

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Discussion Starter #13
Thank you for your reply.

when it’s cold and. has been standing for a while , fx the next day, , there’s no problem . To my knowledge everything, except the brakelights , are functioning ok when the problem is on. If i start the engine, fx after visiting the gas station, it runs uneven in the motor (low volt for the ignition?) and always the brakelight doesn’t work. The speed-pilot functioning ok but Will not turn off when i Press the brakepedal.. Could it be a bad connection in the ignition key house. ?
I always have a full charged battery.
 

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Interesting... Maybe you should try to remove cruise control ECU (speed control unit) and its relays and check if problem still persist? Check fuse too ;)

I believe it is a part of early SZs electric circuit diagram (from http://rrtechnical.info/sz/sz80/szelectricfull.pdf ):
29595


There is a 14CN wire from brake light circuit to speed control unit/ECU and it is the only one that could prevent brake light from turn-on (if diagram is proper for your car). Another suspected part is a "stop lamps failure relay", but IMHO in second order. Of course you could check other elements, like stop light switch, just to be sure ;)

Some users more experienced in early SZ cars could talk more ;)

Please note, that usage of cruise control without ability to turn it off with brake pedal is extremely dangerous(!)
 
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