The interior lights are in parallel not series so only removing one bulb won't break the circuit. Each lamp housing is fed 12v via a black sleeved wire and grounded by a brown sleeved wire. The grounds are all collected together and connected to the door switches and dashboard switch. Every wire in the interior lighting circuit before the switches (black or brown sleeve) will show permanent 12v.
My new challenge - 1964 ID19F Safari
- Thread starter bleudanube
- Start date
Just as you can lightly reface the piston flap valve discs #12 and the mating face on each cylinder, you can also lightly lap the face of the bronze ring and the bearing face. Oiled wet and dry on a very flat surface like a piece of glass. Don't remove too much material, it doesn't have to be perfect and remember sealing with an oil film does want some surface roughness - a whole other topic. You should be able to turn the bearing around to give you a hopefully unmarked face. You can dismantle the bearing to make working on it easier - carefully lift out the plastic cage to release the balls.
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Correct. I just sat it onto it. But I therefore also turned the brass bush over (looks like I had it the wrong way round after assembling it last time). Let’s see how long the o-ring lasts… or not
Wiring issue: excuse my simplistic sketch, but as you know - wiring isn’t my strong point, fault finding even less so…
Bill will know exactly, but this is how I believe the wires are run. Passenger door and rear tail light are in parallel, the driver b-pillar light is in series as I added it later.
The wire is melted on the first 300mm or so, after the 12V feed from the main loom. Why would it melt there and not at the point where the short would be (not sure where that is yet)?
I wired up the door switches trying to follow Bill’s instruction. If I made an error there, could that create sufficient resistance to melt a wire? I wouldn’t have thought so… but could I have gotten positive and negative wrong?
The interior door lights have barely been on as I normally turn them off while working on the car to not drain the battery. That would also fit why the issue hasn’t appeared earlier.
Re the continuity ‘beep’ on the multi meter: both wires on each interior light (blank wire ends - fittings removed) create a ‘beep’… I would have thought only the positive wire should beep, not the ground wire - they can’t both go back to the melted male plug that connects to the 12V from the main loom! This leads me to believe that there must be a spot where those two wires/sections touch - which then caused the short?
That should be between the start of the rear loom at the dash and the top of the c-pillar where the wiring splits into the wires for the passenger b-pillar light and the rear boot light…
Am I completely off the mark? Is there an easier way to find the trouble spot?
Sven
All the bulbs are out and the fittings also removed … so all I have is two bare wires sticking out that are not connected.
You may have a dead short close to where the melted portion is. It would most likely be in the lightest gauge wire section between the supply and the point at which it is shorted. Perhaps, you pinched it behind the heater/vent unit or inadvertently put a screw into it near the melted portion? If there are two wires supplying the +12V per your diagram, then the current drawn could be split between these and they may not become as hot as the single black wire that has melted. Or the gauge of the wire in the main harness could be slightly thicker than the part that melted. There could still be more damage that you can't see.
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I'm no electrical expert but I think (regardless of where the short is) the wire will heat up at the end nearest the power source due to the inherant resistance of the wiring between the power source and the actual short.
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But it's $25...... still worth it?
That effect will not be significant. It's the equivalent of worrying about smoking reducing your lifespan on the deck of the Titanic after all the lifeboats have already left. The current being carried is the same at all points of the circuit, but the size of the conductors involved vary and results in different amounts of heating. An incandescent light globe is an example of this, where the whole of the filament heats up very rapidly, while the supply wiring barely warms over a long period.
Definitely! Didn’t even know until a few days ago that we can donate …. Is that the reason for shutting? Insufficient funds or sponsors? Will the $25 be sufficient or what would it take to retain Aussiefrogs as is?
Anyway, let’s start with $50 for now and hope it helps!
A 10 amp wire (supplying 12V DC) is only rated at 10 amps up to 6 metres in length, at 12 metres in length the same wire is only safe for 5 amps of load and the available voltage will have dropped by 2 to 3%. Not really insignificant?
See "Ohm's law".
Please explain?
I don't think you are correct.
The increasing length is not a safety concern, you could make it 100m, it's still going to have the same resistance per metre. Therefore the same heating.....
IF..... you have a load which will draw the same current regardless of voltage (which we don't).
The voltage drop due to resistance will reduce the current (Ohm's law).
It's not a safety concern, it may be a circuit performance concern, where you want to maintain voltage at a distance.
2 to 3% voltage loss is not significant.
There are plenty of automotive systems that operate at a nominal 12V, but operate as designed in a range from say 11V to 14.4V
I know of a 12V DC system that drops below 10V for a couple of seconds during a start up, and this is considered acceptable by the system designers.
That's a voltage drop of more than 25%, from a standing voltage of about 13.8
Yes that is significant.
I think you got your wires crossed (ha). The rating doesn't say the cable is not safe at 12 metres. It says at 12 metres the manufacturer can't guarantee it will still carry 10A because of the loss along the cable. The current will be lower by the way (as the manufacturer very well knows), not higher. Hence less (in theory) chance of an overcurrent (the wire itself becomes a current limiting resistor).
Anyhoo. 3% of 12V is 0.36V. Beyond the limit of a run of the limit meter on the market. I.e. not really significant. Hence a short will still melt the wire.
Oh, and by the way, Ohm's law says the above, not me.
I agree with the suggestion put forward above the wire melt where it had a weak spot from manufacture regardless of where the short occurred.
Bleudanube, I agree with the suggestion above you need to take the bulbs out before you measure continuity. That test you did only says the bulbs are good (they conduct all the way from positive to earth). Which you probably knew already, because they worked.
I do however have a further suggestion. After you take all the globes in the burnt circuit out, it may help you to disconnect all of those branching points if possible and disconnect the burnt wire from +12V and then re-do your test by simply connecting the meter to the burnt wire (right where it's burnt) and ground. If no short is detected, connect one branch back to the circuit, do the test again, until you find the culprit. I would also separate the door switch circuit during the tests and investigate that separately. In theory, this circuit should not be capable on its own to be the problem (because it only has one wire at ground potential), but just to eliminate one source of confusion (and given that we don't actually have the entire schematic) I would take it out.
Bill might be able to help if he has a schematic of your loom given he made it.
Anyhoo. 3% of 12V is 0.36V. Beyond the limit of a run of the limit meter on the market. I.e. not really significant. Hence a short will still melt the wire.
Oh, and by the way, Ohm's law says the above, not me.
I agree with the suggestion put forward above the wire melt where it had a weak spot from manufacture regardless of where the short occurred.
Bleudanube, I agree with the suggestion above you need to take the bulbs out before you measure continuity. That test you did only says the bulbs are good (they conduct all the way from positive to earth). Which you probably knew already, because they worked.
I do however have a further suggestion. After you take all the globes in the burnt circuit out, it may help you to disconnect all of those branching points if possible and disconnect the burnt wire from +12V and then re-do your test by simply connecting the meter to the burnt wire (right where it's burnt) and ground. If no short is detected, connect one branch back to the circuit, do the test again, until you find the culprit. I would also separate the door switch circuit during the tests and investigate that separately. In theory, this circuit should not be capable on its own to be the problem (because it only has one wire at ground potential), but just to eliminate one source of confusion (and given that we don't actually have the entire schematic) I would take it out.
Bill might be able to help if he has a schematic of your loom given he made it.
Plug a 15 amp arc welder straiģht into a 15amp power point and weld away. Add a 20m 15amp extension cord and suddenly we have reduced performance (ie striking an arc) and,/or start tripping the circuit breaker and never question why?
I have a car with a 1kw starter motor supplied by tiny little 100 amp leads, cranks like a champ and the wiring never gets even warm.
The battery lives under drivers seat and the starter motor is less than 30cm from the battery. Are you saying if I relocate the battery to the boot I can still use 100 amp wiring?
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Correction to previous post the car mentioned uses 8 AWG starter/earth cables which is 50 amp rated.
If your starter is 1kW, (let's assume that's electrical power required) then at 12V, it is drawing (1000 ÷ 12) 83A. If it is connected by 50A cable, the cable will be getting warm, and causing voltage drop, beyond the cable manufacturers specs. However because the starter is not powered for more than a couple of seconds (hopefully) the heating will not be too much for the insulation to handle.
The above is theoretical, because the actual voltage during cranking may be considerably lower, and terminal connections may have more resistance than the cable itself.
If the starter motor has an output of 1kW, then the electrical power required will be maybe 1.3 times that.
Trouble is things aren't always as simple as mathematical equations. I can crank for 15 seconds or so when the car has sat (to get the fuel up) and still no signs of real heat. Not only the cables, but also the battery and starter connections are barely warm to the touch.
However this 1kw starter is only spinning an 850cc engine. I guarantee if the same circuit was supplying the same starter spinning a 5 litre V8 it would go up in smoke in short order even though none of the "electrical theory" has changed.
The charts I attached states 8AWG is 30 amp (at 5m), yet the cable manufacturer I bought off states it is 50 amp, but they don't specify at what length? I don't really care, as it, and the rest of the car's wiring loom (which I made 6 years ago) has never given one iota of trouble.
We've really gone off topic for Sven. All I said was that the apparent short that he has is not necessarily going to be at the point where the wiring has melted.
I presume the aerodynamics of the luggage container on top is a work in progress ? 
Richard
Richard
Sven, not sure if you’re still having stress with the distributor: My mechanic installed a 123 last week with new coil & cables. Night and day. I think I was the last guy in the USA with a distributor and now I know why.