Failed MOT

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Failed MOT

Post by silverfox »

My TXD failed the MOT yesterday. The CLUNK was bottom ball-joint so wasn't surprised. But I WAS surprised to find that the rear silencer box holding bracket had dropped off between checking underneath and getting to the MOT station!

Also failed is what seems to be an earthing problem in the rear light system that I hadn't noticed - with the lights on and indicating at the same time one affects the other with a dulling of the lights on and off intime with the indicators - any ideas? There used to be a high level brake light on the boot lid but its been removed - I wonder! :cry:
Me depressed? Don't make me laugh!

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Post by jeremy »

Light problem is almost certainly earthing - I think you'll find the earths behind the light units - make sure its clean and also that all plugs and contacts are clean as well. The contacts and strange metal strip circuit system in the light units are a bit prone to corrosion which can cause problems and is quite dificult to shift. A little TLC will sort it all.

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Post by Way2go »

A good way of checking out earthing problems on higher current drain circuits is to make a good chassis contact with the negative of a multimeter, set to voltage (12V). With the lights operating measure the earth circuit wires ONLY at each of the bulb ends and note the voltages seen. It is likely that the highest voltage recorded will be the earh line that has the problem!

If you have an AVO or similar with a 10 amp current range then you could switch to this range and again apply the + probe to the suspected earth at the bulb end. 2 things will happen if this is indeed the faulty earth; 1) The bulbs will brighten and not pulse. 2) the meter will indicate a current.
(CAUTION while on the current range do not apply the probe to the +12v feeds or you will get sparks and probably damage the meter.)

When you have found the offending earth line, clean it at the bolt ends at the chassis and the lamp ends. Inspect the wires for corrosion at the crimp points.
1991 BX19GTi Auto