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Bad Electrickery Day


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Jumped in the 6 to go to Halfords to pick up 2 new bicycle tyres ( back up vehicle!!). On the way the 15 amp fuse blew, no fuel, temp or indicators, so lots of arm flapping all the way into town, even though nobody understands hand signals these days, apart from the 2 fingered variety! Managed to buy new fuse, so all well in that respect.

 

On the way back I decided to test the other electric bits - the horn has stopped working and the nearside headlight lights up but is very dim. The offside light is fine.

 

Now, this car is a bit of a voyage of discovery for me, which is fine, but a bit frustrating!

 

I can't even find the horns let alone fix them - so how do I go about tracing the fault? (forgot to mention, the MoT is imminent!)

 

As for the light, I have a spare bulb which I haven't fitted yet, but could it be a poor earth, rather than a bulb?

 

Any 'TR6 for Dummies' advice welcome.

 

Cheers

 

Terry

 

 

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Hi Terry

 

Horns are in front of the radiator, low down, they have a relay in their circuit.

 

I suggest you learn basic electircal testing, very easy for 12v systems and i believe there is a '12v electrics for dummies' book!

 

Good luck !

 

Steve

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Quick fixes, like short cuts usaully end up taking longer!

 

The fist step towards becoming a sparky is to get a multimeter.

A bulb on some leads can useful but not as!

 

The first thing it will do is show you if your dim headlamp is due to reduced voltage compared with the other - a dim lamp is rarely faulty, just not well energised.

Horns - compare battery volts with volts at horn terminals - horns need a good feed to sound or they don't at all.

If the horn volts reduced, trace the wiring and connectors, testing for a volts drop.

 

And a fuse rarely goes without a reason. Something has blown it, that allowed a high current to run through the circuit so that the fuse gave its all to save your wiring from a smoke release.

When inspecting as above look for worn insulation, connector out of place.

 

You'll soon be an expert!

John

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Have you tested the fuse? some times the holder fails to make a good connection. If the fuse has blown is the metal wire inside vapourised (you have a serious short in the system) or just broken. If its broken worth replacing it first as they do fatigue and break.

Yes you need a decent meter and a copy of the cct diagram for your car, should be able to find one with a quick Google.

 

cheers

mike

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Thanks all,

 

I do have a multimeter, I guess I just need some guidance in how and where to apply it. For example:

 

"The first thing it will do is show you if your dim headlamp is due to reduced voltage compared with the other - a dim lamp is rarely faulty, just not well energised."

 

So how do I actually test if there is a reduced voltage, and if there is, what do I do then?

 

It is not actually a 'quick fix', I.e. A bodge job, that I want, just some idiot proof guidance about how to do things properly until such time as I have learned a bit more.

 

By the way, what is a cct diagram? Google brings up Continuous Cooling Technology!

 

Thanks for all your patience!

 

Cheers

 

Terry

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Hi Terry,

all the electrical things on the car are attached to the earth (body of the car, -ve of the battery)

Connect the meter black wire (-ve) to the battery -Ve pole

Select a low Volt range on the meter (DMM) that is higher than 12V.

Place the other (Red) wire of the DMM on the +ve pole of the battery -

it should read apprx 12v. If a little higher, fine. If a little lower then that may be a problem for later.

 

The head lights are powered by either Blue/Red or Blue/White wire.

Place the DMM red wire on a connector close to the head light.

On the good head light the voltage should be very similar tot he battery volts - within 0.5V.

The bad head light will/may give a lower voltage - if yes then go back along the cable to see where the volts rise to that of the battery. If you get there then great.

 

If you did get 12v close to the headlight then it could be the earth return - check the black earth wires coming from the headlamp unit.

 

Next lesson will be hard wiring the interocitor into the cigar lighter socket.

 

Roger

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Terry,

It is very difficult to explain fault finding if you have no experience, vut here is an attempt, it is definitely not a full procedure

Let's take one step at the time:

The headlamp issue.

Put your multimeter on volts.

Connect your multimeter to the positive (+) and negative (-) poles of the battery. Black goes on negative, red on positive

It should read 12 to 13 V, if the engine is not running, and approx 13 to 13.5 V if the engine is running.

For this testing, the engine does not need to be running, but connecting a battery charger will help to maintain the battery charged.

Now put the red (+) wire of the multimeter to the blue/white or blue/red connection to each headlamp, as close to the bulb as you can get.

Compare L and R values. You may need to open a connector. B/w and blue/red are for main and dip, so only one should show volts.

If both L and R are the same (they should be), the feed to the bulbs is ok. It can then be a bad earth or different bulbs (wattage).

So now check the ground to earth, clean it, or make a bypass to the chassis.

This is a first stem, no more than that.

Good luck.

Waldi

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Terry-

 

Welly, NZ? If so-PM me w a ph number.

Joined the NZ TR register? LOTS of useful types there to help

 

Matt

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Actually...scrub that. Our NZ "Halfords" just sell potatoes & from Fielding!

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Following the advice from Roger and Waldi, I get the following results:

 

Across the battery with the engine off 13.38v

 

Nearside:

 

Dip 12.4v

Main 12.4

 

 

Offside:

 

Dip 12.52v

Main 12.4v

 

I guess these are within acceptable limits (?), so it looks like an earth problem on the near side light, which is the dim one.

 

I tried to trace the earth wire back, but it soon disappeared into a wrapped bundle of wires, so it may be a case of setting up another earth from just behind the light fitting

 

Terry

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Hi Terry,

Well done:)

Yes, to verify if the earthing is the cause, you can add a temporary wire to the body.

If you follow the wiring loom, you may find the earthing wire, it is a black wire.

Also, open, inspect and clean all connectors, they are also indicated in the wiring diagram.

Waldi

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Yes, well done! due to Roger and Waldi, not me.

 

Your 'meter is multifunctional and versatile, and can check the earth as well, as Roger referred to.

 

Set it to a Resistance (Ohms or an omega sign Ω) range , and a low one, 200 Ohms or less.

Disconnect the earth return from the headlamp and test the return wire as above (Earth clip on negative battery post, red probe on return wire)

It should show a low, fractions of an Ohm, resistance or none.

OR, it will not read at all. 'Meters vary, but it may show a "1" at the other end of the display to the true reading - this indicates an open, non-conducting, circuit - there is no earth!

 

Lights are fascinating creatures and not just to moths. They will find other ways to earth, if their main route fails, earthing through other circuits and even the bodywork.

If there is no earth wire earth, or a high resistance, then try the same earth test on the contact on the headlamp. You may find that there is an earth there, a poor one, which keeps your headlamp alight, but poorly.

 

A new earth wire will help, or even cure,but the purist will seek the fault in the earth wire! If one wire/connection has failed, others will follow unless the problem is treated.

 

Bests

John

Edited by john.r.davies
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Back in the garage again today. Definitely no earth connection to the headlight. I tried to trace the wire back, but it disappears into bundles in the back of beyond, and I would probably do more harm than good pulling the harness around.

 

I tried a temporary earth connection which worked, so that is definitely the problem.

 

So, although it is not the best engineering solution, I am thinking of putting a new earth cable from the chassis to the light. There is a convenient earth point at the back of the headlight which is where the small side light in the headlamp is earthed.

 

If I cut the earth wire which goes into the back of the bulb plug about 6 inches or so from the plug, and connect that to the earthing point, will that be a reasonable fix, or could I be creating other problems?

 

Many thanks for your patience

 

Terry

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There is a earth point on the front valance, behind the grille, not sure though if it is also for the headlamps.

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