how to test a switch

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Trailpug

Trailpug

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Norwich, Norfolk
I know the answer is bound to be simple but my fuddled brain is just not getting it!
My reverse light has given up the ghost! No power to the light unit switch connection block seems sound so i am assuming the switch is the next thing to check is it just join the two cables from the switch together or something like that whilst in reverse with ignition on? or use a volt meter?
R380 gearbox, 300TDI Defender
Any advice would be grateful.
 
Get a test lamp on it, much easier. Stick it in reverse with the electrics turned on and connect your positive and negative from the test lamp to the spade connectors on the reverse switch (it doesnt matter which way round they are). If it doesnt come on try screwing the reverse switch in more whilst checking it, if it doesnt work when its screwed in all the way then youll probably need a new switch. They cost buttons anyway
 
Like the wolf said. It will be the switch but before y do anything. Make up a short wire with both male connectors crimped and then pull the two wires from the switch and bridge it with the short wire u made. And select reverse with ingition on. If light comes on that tells u it is the switch. If no lights it is not the switch etc.
 
Taffy said:
Like the wolf said. It will be the switch but before y do anything. Make up a short wire with both male connectors crimped and then pull the two wires from the switch and bridge it with the short wire u made. And select reverse with ingition on. If light comes on that tells u it is the switch. If no lights it is not the switch etc.
Click to expand...

That wouldnt show anything as the switch then wouldnt be getting a live connection. One of the spade connectors on the switch goes to the reverse light and the other goes to a live.

Actually just realised that i made a mistake in my last post. If you can identify which of the original wires is live then leave this connected before using your test lamp and just earth the test lamp on a part of the bodywork. Its a pretty simple setup so chances are it will be the switch. Mine wasnt working though and i found out that it was the wire which was supposed to go to the reverse light so i just made up a new wire and ran it back; still needed a new switch mind you.
 
I take it you have got a multimeter? (if not get one, they are very handy pieces of kit and cheap)

All you need to do is check the switch is check whilst its NOT in reverse there is infinite resistance between the terminals (i.e. no reading, will be a - on the screen usually). Now select reverse and you will find that there is a resistance reading now, this is because the switch has made contact and will mean its working, if it still has no resistance then it hasn't made contact and is faulty.

If the switch is working then you need to check for a 12v supply to the switch, if there is no supply then you need to work backwards till you find it, first port of call will be the fusebox usually.
 
That wouldnt show anything as the switch then wouldnt be getting a live connection. One of the spade connectors on the switch goes to the reverse light and the other goes to a live.

Wolf eh ?? The wires to switch are live positive. U confusing this poor chap. If u pull both wires out of switch and stick together and put in reverse and switch ingition on the reverse lights should light up. This will tell u it is switch faulty if lights don't light up then u know switch is okay. And trace back the fault etc
 
Taffy said:
That wouldnt show anything as the switch then wouldnt be getting a live connection. One of the spade connectors on the switch goes to the reverse light and the other goes to a live.

Wolf eh ?? The wires to switch are live positive. U confusing this poor chap. If u pull both wires out of switch and stick together and put in reverse and switch ingition on the reverse lights should light up. This will tell u it is switch faulty if lights don't light up then u know switch is okay. And trace back the fault etc
Click to expand...

There would be no need to put it in reverse, you have just taken the switch out of the equation but yeah, connecting the two wires is the quickest option although if it still doesnt work it doesnt mean the switch is faulty, could be something else...
 
Taffy said:
Wolf eh ?? The wires to switch are live positive. U confusing this poor chap. If u pull both wires out of switch and stick together and put in reverse and switch ingition on the reverse lights should light up. This will tell u it is switch faulty if lights don't light up then u know switch is okay. And trace back the fault etc
Click to expand...

What Jon said. Out of the two wires already connected to the switch one goes to the reverse light and one provides a live. When reverse is selected it presses the switch and completes the circuit. This is what i was saying. If you take both wires off the switch then youre not exactly testing the switch are you
 
Yes the wolf. You are correct. What I was saying was. Fault tracing. Bridge the two wires gives live circuit and if it light up we know the wiring system is okay if no lights. We know no live current going through. Then we begin using lamp or volt meter and doing what you said.

I think we have different idea of fault tracing. But end result would be the same
 
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