Fuse 3 blows instantly - Page 2

stocktake · 31st March 2011, 05:39

Quote:

Originally Posted by HarryM1BYT

Rather than repeatedly replacing the fuse, wire a 6w lamp across a blown fuse and waggle the wiring about in the relevant areas - when the lamp goes out or flickers, you have found the short.

What a brilliant Idea

Number 6 · 31st March 2011, 08:01

Quote:

Originally Posted by stocktake

What a brilliant Idea

I wish I was that clever............

Mike Noc · 31st March 2011, 08:31

Quote:

Originally Posted by raykay

If the fuse is blowing because of a short, it means that somewhere along the live side if the circuit after the fuse, something is touching earth.

As HarryM1BYT has said, if you replace the fuse with a lamp, it will light as it has 12v from the live side of the fuse holder and earth from the the fault in the circuit on the other side of the fuse holder.

The lamp will go out when it loses the connection to earth when the fault has been found and rectified.

Ray totally agree. I think you have quoted me out of context as both Harry in his post before mine and me were answering TC's original post, which has since been edited, so neither of our answers make sense. I was just agreeing with Harry that this is exactly what bulbs are designed to do - light up in an electrical circuit ie positive to ground, whether its an accidental one as in a short or not. Have used this method many times myself when I haven't had my multimeter handy.

Mike

Bolin · 31st March 2011, 23:41

Well, I checked the diagnostic socket, and it appeared perfectly fine, so it looks like I will try the bulb idea, or put a multimeter buzzer across.

Does anybody know where I can get a complete wiring diagram from? Haynes doesn't cover everything.

chrissyboy · 1st April 2011, 07:40

you need to find a wiring diagram to follow as it sounds to me like a diode in the circuit has gone allowing emf to flow back and instantly blowing the fuse . failing that the wires sitting in the water may be the problem

Mike Noc · 1st April 2011, 07:57

Chris if voltage flows back up to the fuse then you end up with +12v on either side of the fuse and it won't blow. This sounds more like a short to ground and probably due to a damaged wire, component or water getting in where it shouldn't.

Mike

jcwatrichmond · 1st April 2011, 08:11

Do a Google search for r75_body_electrics.pdf

I downloaded it from somewhere but I can't remember where.

JCW

PS. http://www.rover-club.net/graphics/m..._electrics.pdf

Bolin · 2nd April 2011, 16:17

Thanks for the link - a useful document.

I have tried 'buzzing' all the connector pins to earth to look for a short. Other than black wires (which should go to earth I think!) I found that the red/white wire to the clock went to earth as did the black/slate wire on the 8-pin seat connector.

Can anybody help tell me if these should go to earth or not? This test was done with no fuse in place for the obvious reason! and battery disconnected.

raykay · 2nd April 2011, 16:38

Red/White is the positive feed for the clock illumination, Black/Slate is an ECU earth connection.

Bolin · 2nd April 2011, 18:43

Many thanks raykay, I now know that the black/slate wire is not to blame. How do you know this and do you know where I can get a wiring diagram for the seats from?

I had guessed that the red/white wire was for the illumination, as the other coloured wire was purple, which tends to be permanent 12V. It shouldn't be earthing though, should it? Even so, I don't think this would be related to fuse 3.

I have found that Haynes has a partial wiring diagram for the clock and diagnostic connector, but it shows them using fuse 28, 15 amps not the 5 amps that is my fuse 3. I assume this is for the later wiring harness and fusebox.

1st April 2011, 07:40	#15
chrissyboy This is my second home lovely little ford focus. Join Date: Jul 2009 Location: East Dulwich Posts: 7,877 Thanks: 2 Thanked 82 Times in 68 Posts	you need to find a wiring diagram to follow as it sounds to me like a diode in the circuit has gone allowing emf to flow back and instantly blowing the fuse . failing that the wires sitting in the water may be the problem __________________ [ I'm really confused. -I keep dreaming I'm an insomniac

1st April 2011, 07:57	#16
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,569 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Chris if voltage flows back up to the fuse then you end up with +12v on either side of the fuse and it won't blow. This sounds more like a short to ground and probably due to a damaged wire, component or water getting in where it shouldn't. Mike Last edited by Mike Noc; 1st April 2011 at 08:03..

1st April 2011, 08:11	#17
jcwatrichmond Loves to post Rover 75 1.8T 2003 Club SE Join Date: Jan 2009 Location: Solihull, Posts: 370 Thanks: 0 Thanked 0 Times in 0 Posts	Do a Google search for r75_body_electrics.pdf I downloaded it from somewhere but I can't remember where. JCW PS. http://www.rover-club.net/graphics/m..._electrics.pdf Last edited by jcwatrichmond; 1st April 2011 at 08:15.. Reason: Addition

31st March 2011, 23:41	#14
Bolin This is my second home Rover 75 2.5 V6 Connoisseur SE 4dr manual Wedgewood Blue 2 04-05/06/2001 Join Date: Nov 2006 Location: N.E. Hampshire Posts: 4,620 Thanks: 289 Thanked 308 Times in 243 Posts	Well, I checked the diagnostic socket, and it appeared perfectly fine, so it looks like I will try the bulb idea, or put a multimeter buzzer across. Does anybody know where I can get a complete wiring diagram from? Haynes doesn't cover everything.

2nd April 2011, 16:17	#18
Bolin This is my second home Rover 75 2.5 V6 Connoisseur SE 4dr manual Wedgewood Blue 2 04-05/06/2001 Join Date: Nov 2006 Location: N.E. Hampshire Posts: 4,620 Thanks: 289 Thanked 308 Times in 243 Posts	Thanks for the link - a useful document. I have tried 'buzzing' all the connector pins to earth to look for a short. Other than black wires (which should go to earth I think!) I found that the red/white wire to the clock went to earth as did the black/slate wire on the 8-pin seat connector. Can anybody help tell me if these should go to earth or not? This test was done with no fuse in place for the obvious reason! and battery disconnected.

2nd April 2011, 16:38	#19
raykay I really should get out more....... Now Other Manufacturer Join Date: Nov 2006 Location: Co. Kerry Posts: 2,786 Thanks: 16 Thanked 310 Times in 283 Posts	Red/White is the positive feed for the clock illumination, Black/Slate is an ECU earth connection.

2nd April 2011, 18:43	#20
Bolin This is my second home Rover 75 2.5 V6 Connoisseur SE 4dr manual Wedgewood Blue 2 04-05/06/2001 Join Date: Nov 2006 Location: N.E. Hampshire Posts: 4,620 Thanks: 289 Thanked 308 Times in 243 Posts	Many thanks raykay, I now know that the black/slate wire is not to blame. How do you know this and do you know where I can get a wiring diagram for the seats from? I had guessed that the red/white wire was for the illumination, as the other coloured wire was purple, which tends to be permanent 12V. It shouldn't be earthing though, should it? Even so, I don't think this would be related to fuse 3. I have found that Haynes has a partial wiring diagram for the clock and diagnostic connector, but it shows them using fuse 28, 15 amps not the 5 amps that is my fuse 3. I assume this is for the later wiring harness and fusebox.