Lighting problems

What can cause my headlights & dash light to keep going dim when i'm driving along at normal road speeds? There doesn't seem to be any pattern to it one minute they are normal and the next go quite dim then return to normal brightness again, i have noticed a difference in the electric fan speed if i switch off the car when they are running so don't know whether it is the battery or alternator.

check the plugs at the back of the headlights and earths.

I have checked those, only recently changed the headlight bulbs as i thought the old ones may be a bit passed it but is still doing it. Thanks for replying.

check alternator connection and belt tension.

check the fusable links havent corroded in the loom from the battery on the off side inner wing

top-cat said:

check the fusable links havent corroded in the loom from the battery on the off side inner wing

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I thought they were only fitted on a 200 tdi not the 300? maybe wrong though. Thanks

redhand said:

check alternator connection and belt tension.

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Cheers redhand, belt tension is ok, all the connections on the alternator seem ok but is there a way i can take the regulator pack off to perhaps clean it? I am waiting for an voltmeter to turn up so i can check the outputs of the batt and alternator etc to see what this shows.

smarty1972 said:

I thought they were only fitted on a 200 tdi not the 300? maybe wrong though. Thanks

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Sorry mate it was a 200 i used to own just assumed 300 would be the same. Hope you get it sorted

top-cat said:

Sorry mate it was a 200 i used to own just assumed 300 would be the same. Hope you get it sorted

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Cheers mate, not a prob

I had a similar problem , I thought it was the battary , that was fine though . Turned out that the battery lugs and conectors were slightly corroded . Cleaned them up and all was well .....

Sure it's a matter of bad contact/earth somewhere... another possibility is the lighting switch(cos its a common point for headlamp and instrument pack illumination)....try to shake it a bit while lights are going dim.....if it has some effect then there is the problem.

You have a high resistance somewhere in the lighting supply any loose connection from fuses, plugs, switch to lamp or earth connections could be the cause so a bit of testing to do.

300's have fusable links but now they are in the engine bay fusebox.

Cheers for the replies guys, i have electrical gremlins somewhere as i have noticed speed of the heater fan rises when i switch something else on or press the brake pedal etc. I have checked the main earth strap and that seems to be ok and also the battery terminals are nice and clean(battery was replaced last winter) and nice and tight so unsure what to check next.

Hi Smarty
From what I remember-behind the passenger kick panel there is a main earth ie a metal bracket boltrd to the body with several black wires connected to it-worth a check of the nut that holds it to the bodywork.Mine is a manual but should be similar
Hope that helps

Cheers pauli, i will check that later on today.

Have you checked the condition of the connections on the engine earth straps? If not they are probably due a clean.
The earth straps form the earth return path for the alternator to the battery, if they are not in good condition they are as bad as a faulty alternator connection.

Could also be an earth behind the drivers kick panel as well

There is a multi connector bolted to the steering column. with about 10 earths connected to it. if it's a 200tdi.

Tis a 300 Red :doh:

pauli said:

Tis a 300 Red :doh:

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Probably still got the connector in the same place though??