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Electric help pls morris

The headlight switch on my morris 1000 is of the older style pull type. It was getting extremely hot when the headlights were on- melting the insulation on the sire connecting it, providing the healthy smell of burning plastic and doing so quickly so that a 20 minute drive needed to be interrupted for cooling off periods.

I have replaced the switch - the old one appear very scorched around the headlight terminal.

The new, well second hand one, also seems to be getting fairly hot, to the extent that the dash borad immediately surrounding it is fairly warm after five mins or so, too hot to touch at the terminal for more than a second though not burning the skin off as the other was. I have not had it on for very long and don't know if it will get to the plastic burning stage.

With headlights and sidelights on there is a drain of about 8 amps at the battery, with the motor not running, which seems about right (100 watt or so of lights on).

I'd appreciate advice. Is this normal and have I just become oversensitised to this from the previous switch, in which case I will just make sure that extraneous wires are well clear, and avoid developing a fetish for frequently touching the back of switches- or is there something up?

Many thanks Jonathan

Reply to
JonSenker
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Clearly it's not a short circuit causing an overload, so there must be a high resistance contact or arcing that is generating the heat. Clean the switch with switch cleaner and check all the wiring terminations. There could be some corrosion on the wires or terminals, or a dry solder joint in a bullet. If necessary operate the lights with the switch out of the dashboard and find out exactly what is generating the heat. Your second hand switch could have the same problem as your old one especially if it hasn't been used for a long time.

Reply to
Richard Porter

oversensitised to

Just add a relay so the switch is under only the tiny load of the relay coil.

MrCheerful

Reply to
MrCheerful

A switch that gets hot has got a bad connection, either where the wires connect to the switch or across the switch contacts inside. I would check/clean these as a first step.

Two headlights, 4 sidelights and a number plate light plus a couple of instrument lights would draw nearer 12 amps than 8. Another indication that the connections are running through some form of resistance through a bad connection.

oversensitised to

I think something is up. If you can't fix it with the switch and wiring arrangement you have now (and do you know that the replacement switch doesn't have the same problem as the original?), you could fit a relay to minimise the current running through the switch.

Jim

Reply to
Jim Warren

Like I said earlier. If that doesn't do the trick measure the voltage at both sides of the switch with the headlamps on and off. If there's a voltage drop across the switch with the headlamps on then there is high resistance inside. Check the side/tail circuit too, because it could be generating the heat.

I agree with that, though with headlamps on and without the engine running the battery voltage could be a few volts down.

Reply to
Richard Porter

Much easier to simply connect the voltmeter *across* the switch - this will measure voltage drop across it directly. Saves doing the maths. ;-)

Reply to
Dave Plowman

That's exactly what I said if you'd read a bit further. The point of measuring the voltage at the switch (wrt earth) with and without the headlamps on is that it will give an indication of the health of the battery and wiring up to the switch. Also the current measurement isn't much use unless you also know the voltage because it may be < 12v.

Reply to
Richard Porter

An open circuit voltage measurement is pretty pointless since a DVM takes near enough no current so will not show up poor connections etc. The important thing is voltage drop under load. The best technique is to measure voltage drop from battery to headlight bulb - and do this on the earthy side as well. If the results are poor, you can then go on to measure voltage drop over individual parts of the circuit.

That's why you *start* by measuring the actual voltage drop before anything else.

Reply to
Dave Plowman

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