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 Posted: Sat May 28, 2011 10:56 am |
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Joined: Feb 07, 2010
Posts: 13077
Trade Rating: +65
Location: England
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Right, had my third brake light off yesterday to change one of the resistors because it blew. Left the brake light off overnight, so the wiring connector was exposed [didn't think to cover it up].
Re-fitted it this morning, all the brake lights worked fine.
Nipped out and pulled up in a car park, and a guy said to me "only one of your brake lights is working mate". Turned out only the drivers one was, instantly knew it was the fuse.
Changed the fuse because sure enough it had blown.
Now none of the brake lights work. Fuses are intact but I'm only getting 9.42 volts to my lights, so clearly not enough to light them up. The wires at the switch get really hot as well.
Do you think the only way forward is to re-wire the brake light system?
Cheers,
Lee
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Posted: Sat May 28, 2011 11:00 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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Maybe the shunt resistor was too low value (I assume LED's are involved).
That could have damaged the brake switch and you might well be OK with
just replacing the brake switch.
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sat May 28, 2011 11:02 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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Also remember brake switch is single-pole change-over so it would make sense if
NO or NC contact is permanently closed.
What value resistor are you using?
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sat May 28, 2011 11:04 am |
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Joined: Feb 07, 2010
Posts: 13077
Trade Rating: +65
Location: England
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Changed the resistor for the exact same value. Third brake light worked fine when testing in the house, and initially worked fine on the car.
Just puzzles me why there's only 9.42 volts coming to the lights. Surely if it fried the switch, there'd be 0 volts.
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Posted: Sat May 28, 2011 11:06 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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If the resistor has failed-short that would make a nice divider with the cables going to the brake light
and causing the voltage drop even though its not enough to blow the fuse.
What Ω resistor do you use and what W rating?
Maybe the new one snuffed it. Measure it.
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sat May 28, 2011 11:13 am |
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Joined: Feb 07, 2010
Posts: 13077
Trade Rating: +65
Location: England
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Erm... lost my reference book and threw away the package name 
Resistor is light brown/sandy colour. stripes are gold - brown - grey - brown.
The guy in Maplins said it was the right one.
I disconnected the third brake light, and did a very quick rewire with a relay, but still no joy. Obviously the relay wouldn't activate as there wasn't 12volts.
Original wiring diagram goes like this ......... engine fuse box (f35) > switch > drivers fusebox (f10 & f11) > brake lights (f10 = drivers, f11 = pass & third)
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Posted: Sat May 28, 2011 11:20 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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Gold-Brown-Grey-Brown = 18 Ohms but what Wattage is it?
12V accross 18Ω would be 0.7A roughly which would be at least 8 or 10W
required for the resistor and it would heat up. Could it have melted
the insulation long-term or did you make sure.
I wouldn't worry about the voltage being low as I think the brake switch has had it.
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sat May 28, 2011 11:24 am |
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Joined: Feb 07, 2010
Posts: 13077
Trade Rating: +65
Location: England
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Wattage of what? the resistors? or the brake?
Had a feeling it could have been the switch with the wires getting mega hot.
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Posted: Sat May 28, 2011 11:27 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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The Wattage rating of the resistor. It could be anything from 1/2W to 25W metal or ceramic brick type..
Did it look physicaly the same as the old one or was it smaller in size?
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sat May 28, 2011 11:29 am |
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Joined: Feb 07, 2010
Posts: 13077
Trade Rating: +65
Location: England
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Physically the same. Took it off and shown it the guy, and also took the whole circuit board. Was exactly the same.
Found the pack, all it says is "resistors" on it  And I had to buy 50, t*at
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Posted: Sat May 28, 2011 11:33 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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I would start with replacing the switch making sure you have correct voltage delivered without
the 3rd light connected.
Then make sure you use a hefty resistor to handle the heat and current so you know its not
from there. You should ask for at least a 10W like this:
cgi.ebay.co.uk/10W-Arc...45fadaaa20
Not one like this:
cgi.ebay.co.uk/1-Watt-...3f074509c7
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sat May 28, 2011 11:36 am |
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Joined: Feb 07, 2010
Posts: 13077
Trade Rating: +65
Location: England
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Those resistors won't fit on the circuit board and into the brake light.
It needs to be one like in the second link, as they are soldered to the PCB
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Posted: Sat May 28, 2011 11:37 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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Also, why are you using a shunt resistor for the 3rd brake light for LED's?
I thought it was only required for indicators so it doesn't flash fast because
it thinks a bulb has blown, OR CAN/VAN systems?
EDIT: which pcb?
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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Posted: Sat May 28, 2011 11:38 am |
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Joined: Feb 07, 2010
Posts: 13077
Trade Rating: +65
Location: England
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12volts fried the LED's. Need a resistor every 3-5 LED's. Got them in my front lights as well
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Posted: Sat May 28, 2011 11:39 am |
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Joined: Feb 07, 2010
Posts: 13077
Trade Rating: +65
Location: England
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| V9977 wrote: |
Also, why are you using a shunt resistor for the 3rd brake light for LED's?
I thought it was only required for indicators so it doesn't flash fast because
it thinks a bulb has blown, OR CAN/VAN systems?
EDIT: which pcb? |
The circuit board, that the LED's and resistors are soldered too in the third brake light.
Resistor for every 4 LED's
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