third brake light not working

[ian cox]

Hi,
As stated above the third brake light is not working. The main brake lights work perfectly.
Investigation so far.

I have measured continuity across the OS tailgate strut.
There is 12.5V at the bottom spade connector when the brake pedal is pressed and then 7.5v at the top.
This 7.5 volts appears at the brake light connector, black/yellow stripped wired, BUT only if I disconnect the wires to the brake light. Once connected the 7.5v disappears and no lights glow.
The connector to the brake light has 2 wires in its connector and can only be fitted one way round. All 4 bulbs in the brake light are fine.
Since the brake light uses a wired earth I have unbolted the brake light and plugged it in away for the body. Still the same as above.

I passed an MOT last month so I have no idea if they worked or I needed them to pass.
Ideas. Kind regards Ian

 

[Pkp]

If I understand you correctly, there is a voltage drop of 5V (12.5 - 7.5) across the strut ? This sounds far too high, if you short the strut out, do the lights work ? With the hatch open, you may need to earth the hatch, I cannot remember if the hatch earth is through on of the four contact pins.

 

[ian cox]

Hi
Thanks for the help. Voltage drop across strut is 5v.
Further investigation.
Refitted brake light and interior trim. Still need new shelf cord pegs.
If I miss out the hatch strut and use a wire link brake light works with hatch open. Really cleaned spade connectors on wires tried again not working.
Clipped bottom of strut only in place on 'ball joint' brake light works. hatch open.
Connect both ends onto ball joints not working. Hatch open and closed.
It is hard to disconnect the top of the strut and close the hatch.
The strut is brand new from Ford and so I have unscrewed the ends and change the spade connectors over.
Perhaps I should try the old original strut again.
Kind regards Ian

 

[ian cox]

Hi,
I know it has been a while but to complete the story I have put the old strut back in and all is working again.
The only difference I can see between the new and old strut is that the thread at the top of the strut I slightly longer 3/4mm.
You can buy new from Ford the near side strut but not the off side one. So even though you can unscrew the ends the slightly longer threads may be the key for electrical continuity.
Anyway its working now.
Kind regards Ian