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Hi everyone, hope we are all keeping safe.

Having put the steering wheel straight and corrected the lack of self cancelling of the indicators which were subject of a previous post, I was ready to be back on the road. During pre drive checks I found headlights not working but main beam warning light on  irrespective of dip switch position. Side lights are working correctly. I am at a loss now having checked all cables connected. Any ideas please.

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Side lights are on a separate bit of the wiring circuit so ignore the fact they are working. As well as Roger's comments above, check the dip switch connections. Have a look at the wiring diagram in the link below. If the warning light for high beam is on and the headlamps are off then concentrate on the dip switch (or dimmer switch) and wiring. Is there power via the blue wire to the dip switch. Are the headlamps earthed properly. Do you get power to the blue/white and blue/red wires when you operate the switch.

Good luck

Keith

 

http://www.advanceautowire.com/tr24a.pdf

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Thanks Roger and Keith for the help. Keith, the wiring diagram is simplified with the colouring and I am now concentrating on the dip switch which I have removed and found that I do have power in the blue line. I have bypassed the switch and connected blue to each of the other wires which resulted in power at all three connections at the headlamp connector. Now at a loss today and less hair than earlier. I will try again Tomorrow.

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57 minutes ago, Vic787 said:

connected blue to each of the other wires which resulted in power at all three connections at the headlamp connector.

If that means what I think it does - it sounds as though there is no earth connection to the headlamps, as Keith mentioned.  

Do you mean the three connections to the headlamp bulb?  Without an earth, voltage connected to one will be present on all three as the current flows through the bulb filaments. 

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Yes Rob, with headlight removed, I get power through all three of the connectors in the Lucar adapter.:angry: 

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On the back of a sealed beam headlamp looking at the back. Left pin is main beam, top (middle) pin is earth and right is dip. Each headlamp has 3 wires which go to bullet connectors on the top of the cowl in front of the radiator. The black earth wires join at a bullet connector and there is a third thick black wire from the bullet connector that goes into the loom. Not 100% sure but my bet would be that this is the black wire that exits the loom next to the right hand horn and connects with another thinner black wire under the right hand bolt that fastens the horn to the body. Connect a temporary wire from the bullet connector on top of the cowl to earth and headlamp units should work. If they do then the thicker earth wire going into the loom has a dodgy connection either at the bullet connector or the car body. Previous owners might have connected the earths from each headlamp to the earth points that the sidelights use on the inside front of each wing.

You should only have power in the disconnected headlamp plug on the 2 side pins. The centre pin is the earth. My guess is that the main beam warning bulb is coming on because of a poor earth. Power is trying to earth through the bulb. Has happened to me once. The main beam light came on once when I pressed the horn. It was bad earth on the horn. Never did figure the logic of that one.

Keith

 

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Keith, explained in my terms as I understand you. I am a qualified Coach Trimmer and Vehicle Builder and can get around the mechanics.

Electrics is like platting mud to me.

I completely rebuilt the car in 1996-7 ex Californian so any fitting problems are down to me. I will follow your directions tomorrow so watch this space.

Cheers.

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At a total loss now. So far disconnected indicators and horn, cables I was working on. Checked all black wires on lighting side of loom, only one is visible at the front of the car where it joins n/s headlight loom to main loom, the joint is clean. The main loom continues unbroken to behind the dashboard but I cannot, short of removing the dashboard itself, see a black wire emerge from the loom. Looks like it needs to be seen by an Auto Electrician. 

Thanks for all your help, learnt a bit, so keep safe. Cheers

 

 

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Hello Vic

Oh dear. Back to basics. Each headlamp has 3 wires. The centre pin connector is the earth. Try connecting this on each headlamp to earth with a temporary connection. Take a wire directly from battery terminal to the 2 dip switch outputs. By battery terminal I mean the terminal connected to the starter solenoid. Blue/red is dip and blue/white is main beam and warning light. Headlamps should work. If they do then disconnect temporary earth. If they then don't work then the fault is the earth. If they don't work with the temporary earth then look for the bullet connectors on top of the radiator cowl. The Blue/red (dip) and Blue/white (main) ones are the power to the headlamps. You could put a feed directly from the battery to these bullet connectors. If the lights still don't work then maybe the headlamps have a fault. On a sealed beam unit, if there is a crack in the glass then the air can get into the lamp and they won't work even though the filament is intact. You will still get a circuit though.

Not sure why you have disconnected indicators and horn because they are on different circuits.

I am assuming that you don't have headlamp relays fitted and the wiring is 'standard'. Just spoken to a friend of mine who has had 2 TR4's and we both agree that there should be several bullet connectors situated on top of the radiator cowl. These include headlamp dip, main and earth connectors. Some TR4's were positive earth but this makes no difference to this problem. My friend's early 1962 TR4 was one of these. His current TR4 is negative earth but as I say don't worry about that. Sometimes you will find the headlamps black earth wire connected to the earths on the inside front of each wing. This is the same place that the sidelights/indicators may be earthed to.

See if there are any TR4 owners near you that can help.

Keith

Edited by keith1948
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Hi Keith,

Toys back in the Pram and a tot of Scotch and back on form. Up to now I have located the earth wires, in the case of my car, behind the front valance. I earthed each side and proved headlights work and dip switch ok but earth wire got rather hot. The side lights have a separate earthing point.

It appears not all TRs are the same bearing in mind this original body number is 34xx.

The loom was fitted when I rebuilt the car from left to right hand drive and no relays. I have bypassed light switch to isolate any problems there but that works fine.

I have started removing  the glove box and gauges to gain access to the wiring loom behind the dash to try and locate the end of the black wire and having just read your reply, I think the earth is the fault as only headlamp circuit earth is live. However before delving into the depths of the dash I will follow your suggestions.

I follow up tomorrow. Cheers Keep Safe.

 

 

 

Edited by Vic787
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Hi Vic,

If a wire is getting hot, it is passing too much current for the thickness of the wire, and acting as a resistor. This will cause a drop in the available voltage making your lights dimmer than they should be. So you need the answer to the following question "Is the wire the right diameter, or is it passing too much current?" If the latter, then there is a short circuit somewhere in the circuit. If the former, The wire is not thick enough.

Two 60Watt headlamps at 12 volts pass 5 Amps each so the wire needs to have the ability to pass 10 Amps without getting hot. (i.e. allow for at least 17 Amps to allow for a current surge when the lights are switched on and the fact that the battery voltage is greater than 12 Volts).

You might want to consider that the thicker the wires the smaller the voltage drop along the wire, which means more available voltage will be applied across the lamps giving brighter headlamps so it is better to have thicker wires in the headlamp circuit.

Check Current ratings against the wire thickness on one of the websites that supply wires and see if yours are suitable.

Good luck

TT

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Hello TT,

Taking note of your informative comment, I assume that all wires on the car are of the correct values as it was a new loom although 24 years ago.

i have split the earths at the bullet connectors at the front of the car and made each headlamp its own earth, they now work.

I found the other end of this earth wire where it exited the loom behind the dashboard. It is connected by a bullet connector to both indicator warning light and windscreen wiper switch earths but removing the offending wire failed both of them even though it is now disconnected from the headlights.

At the moment, on the face of it, everything is working although I still have power in the offending wire. 

What are your thoughts on this please, I am at a loss.

Vic

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If I can jump in here, it seems to me that you have proved that a bad earth is the cause of your trouble. By giving each of the headlights it`s own earth you have them working. The wire you have traced up to the indicator warning light and the wiper switch needs to be connected to a good grounding point too, which it would seem was originally together with the headlight earths,  and I suspect that there was a short length of black wire connecting the group to the body of the car which has become lost or displaced, or maybe it is still there and just needs cleaning where it attaches to the body.

I have always found it easier to think of electrickery as water flowing through a hosepipe with the battery as the reservoir. For an item to work it has to flow from the reservoir, through the pipe to the item in question, whether that be a lamp or a motor, and then back to the reservoir. A break anywhere in the circuit and it wont work, a restriction (like a bad connection) being like a kink in the pipe, slowing down the electrons so an item will not work as well as it should.

Ralph

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Hello Vic

Agree with TT above regarding hot wires. However a new loom changes things because anything may be different to 'standard'.

Earthing each headlamp to the inner wings has resolved the headlamp problem. This means the 3rd wire from the bullet connector is not earthed as I thought.

Now the live black wire. Black wires are earth wires and will show voltage on a meter if the item they are connected to is 'on' because the meter is simply completing the circuit. On my car with an original loom, both headlamp earths go to a bullet connector on top of radiator cowl and a thicker black wire goes from that to the loom close by. Then I have a thick black earth wire exiting the loom next to the right hand horn where it is earthed under the bolt holding the horn on. Without taking this apart I am not sure this is headlamp earth but is likely.

The wiper earths on my 4A are next to the wiper motor, one from the switch and one from the motor for the wiper park circuit. On mine nothing to do with the headlamp earth. There is a constant supply to the wiper so the park works. This might explain the earth wire being 'live'.

Sounds very much like the new loom was not wired exactly same as original loom. I think the wire to the wiper and indicator warning isn't the one you think it is coming from the headlamp bullet so I would reconnect that one. Then have a thorough search of the loom from the front of the car as far as the bulkhead in the engine bay looking for a thick black wire poking out of the loom. Once you find it then make sure it is earthed properly. Just another thought - the thick black wire from the original bullet that the headlamps were connected to - isn't connected to any other bullet that it shouldn't be.

Keith

p.s. Just disconnected the thick black earth wire connection under right hand horn mounting and it definitely connects to the bullet earth for headlamps on top of radiator cowl. There is a thinner wire attached at the same point that seems to be horn earth. Both wires exit the loom at this point.

Edited by keith1948
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Hi everyone

Thank you to everyone for the interest, help and advice in the build up to a solution to the problem. I am still at a loss of what caused the failure but now, after tracing, cleaning existing and constructing new earths, I have all electrical instruments and controls working. I still have a dead black wire in the loom which exits at the front and behind the dashboard with no other exit from the loom. There are no earth wires to horns.

I have learnt a lot about  electrickery  (Ralph) but I will still keep away from it and hope that this has solved the problem. We shall see, I will be checking for hot wires for a while yet.

Massive thanks, keep safe

Cheers Vic.

 

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