Brake lights not working?

[John Vine]

Good stuff, JK!

...when I put a probe on each terminal on the switch the multimeter reads the number 1 and when I press the plunger on the switch it stays the same, nothing happens, it still reads the number 1.

Note that the switch turns OFF when the plunger is pressed in (its rest position).  When you apply the brakes, the tab on the piston rod moves rearwards, releasing the plunger and turning the switch ON.

Now that the switch looks to be prime suspect, what happens when you short the wires on each side of the switch together (with ignition on)?

JV

[Jonathan Kay]

Thanks for that, John. I didn't have one in front of me, obviously.

Shorting around the switch would be a very smart move. 

Jonathan

 

[DirtBuddha]

Fixing the CC brake light switch is a 5 minute job. The spring isnt that ferocious at all, just prise end cap out gently and keep your hand over to restrain the small spring. You'll find a u-shaped contact inside ... the legs just need squeezing together a little. Clean any greasy gunk off them.

 

I'd already tried that but to no avail... 

[DirtBuddha]

Now that the switch looks to be prime suspect, what happens when you short the wires on each side of the switch together (with ignition on)?

 

Do you mean like using a test light (as in the type that is a small screwdriver type thing with a probe, and a wire at the other end with a crocodile clip?)  

If so, I tried that before and no dice...  the test light lights up when the two terminals/wires going to the brake switch get connected, but teh brake lights didnt come on...

[SM25T]

The resistance in the body of the screwdriver will prevent current flow ...otherwise testing 230V would kill you. Just use a bit of wire or the jaws of the crocodile clip to short across the terminals.

[Jonathan Kay]

No. A direct connection (short) between the input and output wires at the switch. That makes the switch irrelevant. And (with the ignition ON) the brake lights should come on. And if they don't there's a fault somewhere else.

Edited, crossed post with SM25T's.
You can connect across the switch terminals if both wires are still connected to them. Otherwise connect between the wires.

Jonathan

[Jonathan Kay]

"Note that the switch turns OFF when the plunger is pressed in (its rest position).  When you apply the brakes, the tab on the piston rod moves rearwards, releasing the plunger and turning the switch ON."

I'd missed this. I suggest testing the continuity through the switch with the plunger fully released, if you haven't done that already.

Jonathan

[John Vine]

Re #29:

As JK says in #31, to short (that is, bypass) the switch, connect a length of wire across the terminals (with ignition ON):

If the rest of the circuit is OK, the brake lights will come on.

PS: Great photos in #23!

JV

[DirtBuddha]

Ah - ok, gotcha!  I'll try doing that tomorrow and will reply. 

[DirtBuddha]

Ok guys - I shorted the switch with a wire and YES the brake lights turn on. So indeed the switch has gone bad. 

 

I've ordered a new one from Car Builder Solutions. 

 

Many thanks for all your help - and hopefully all this info will help others in future. 

[Jonathan Kay]

Thanks for letting us know. 

Jonathan

[John Vine]

Thanks for the feedback.   And a good scoreline:  BC 1, electrical gremlins 0.

JV