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It was MOT time.........
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RotaryBri



Joined: 20 Dec 2007
Posts: 465
Location: Warwick

PostPosted: Sat Aug 13, 2011 1:13 am    Post subject: It was MOT time......... Reply with quote

I had checked my Ro80 over a week before the MOT and watched the brake readings when it was on the rollers - nicely balanced now with the new calipers. I then sat down and started to read the local newspaper and then the tester came in and said those dreaded words - I'm sorry it has failed!

What on I asked? The headlamp main beams are not working he said. Sure enough they had stopped functioning. He asked if I had a workshop manual and when I said yes he said that he could sort it out the following day if I could not find the fault.

So off home I went and then started to find the fault. As the dipped beam and main beam have identical relays I swopped the connectors over and found that the dipped beam still worked but not the main beam. The fuses were all intact and twisting them to get a better contact did not change things. I took out the fuse for the dipped beam and they did not work. I then took out the fuse for the main beam and to my surprise all the headlamps including the main beam came on! What a strange thing to happen. The headlamp flasher worked as well without a fuse. I gingerly replaced the fuses and they all still worked perfectly.

So it was a quick trip back to the garage and got a pass certificate.

It has been over 50 years since I passed my 'principles of electricity' exam and I cannot think of an explanation as to why the lamps work without a fuse in the circuit. Can anyone enlighten me?
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RotaryBri

1976 NSU Ro80
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Sat Aug 13, 2011 1:11 pm    Post subject: Reply with quote

It sounds like you aren't identifying the correct fuses.

Peter
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1939 SS Jaguar 2 1/2 litre saloon
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RotaryBri



Joined: 20 Dec 2007
Posts: 465
Location: Warwick

PostPosted: Sat Aug 13, 2011 4:25 pm    Post subject: Reply with quote

Peter,

They were the ones listed in the handbook and also from the wiring diagram in the workshop manual.

The interesting thing is that I also took out another fuse which covered the dashboard illumination and fog lamps (which had not worked for months) and when I put the fuse back the front foglamps and the dashboard lights now worked. The rear foglamps still do not work. Strange isn't it.
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RotaryBri

1976 NSU Ro80
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PAUL BEAUMONT



Joined: 27 Nov 2007
Posts: 1281
Location: Barnsley S. Yorks

PostPosted: Thu Aug 18, 2011 1:19 pm    Post subject: Reply with quote

In my experience wierd automotive electrical happenings usually imply an earth fault somewhere.

Paul
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Churchill Johnson



Joined: 11 Jan 2011
Posts: 359
Location: Rayleigh Essex

PostPosted: Thu Aug 18, 2011 9:30 pm    Post subject: Reply with quote

If you follow the correct feed to the fuse for the light's then from the fuse to the light's then look for any possible back feed when the fuse is removed, and has been suggested chec the earth's as these can allow a back you don't see it much today but a few year's ago some older car's when an indicator or stop-light came on then sidelight's would also come on,again caused by a bad earth.
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