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MG MGA - lighting to ignition

Does anyone have a quick and easy way to change the lighting circuit so it activates from the ignition switch? I know its probably obvious but wonder it there are hidden issues with the circuits, loads and fuses.

My headlights and fog lights are on their own relays and use the normal circuitry to power up those relays. I have a battery kill switch too.

I use my running lights (with led bulbs and side lights in the headlights powered together) as daytime running lights. Of course, 99% of the time I forget to turn them off when I cut off the engine.

For whatever its worth, I have a single 12 volt battery and positive ground (light bulbs don't care).

Simple?

Thanks,

Ted
Ted Persons

Ted
if you intend operating the lights via the ignition switch then you really should use a relay to handle the current and just use the ignition switch to trigger the relay.
The ignition switch is not really up to handling all the additional current used by the lighting circuit and I wouldnt be surprised if it would actually burn out if you also feed the light through it.

See Barneys simplified electrical circuit diagram which fully shows how the lights and the ignition circuits work (link attached)
http://mgaguru.com/mgtech/electric/circ_a.htm


You may notice that the standard MGA lighting circuit doesn't have a fuse in it.

If you are going to fit a relay I would strongly recommend that, at the same time, you should fit a fuse in the lighting supply circuit to protect the wiring in the event of a short circuit.

( I fitted one after I accidentally short circuited this wire and burnt out the entire front wiring harness in the 30 seconds that it took me to disconnect the battery.)

The fuse needs to go into the brown/blue wire (after the ignition switch) which is main the power feed for the lighting supply.

Also, when you do any wiring, disconnect the battery first and use a battery charger to test the lights to make sure everything is correctly wired up before re-connecting it.

If you need a wiring diagram for the relay, let me know.
Also see Barneys ET-206A for relay info

Colyn
Colyn Firth

Because you already have relays in your lighting system, the extra load through the switch is only the minimal extra to activate the relays, so it should be fine. Just isolate the existing live feed to the lighting switch and replace with a feed from the switched terminal (green) of the fuse box. Adding a fuse is always a good idea for the lighting circuit, but you need to add this in the relay power supply. The advantage of adding the feed to your light switch at the fuse box is that this connection is already fused for the relay switching.

Now who supplies good quality light switches as mine has given up the ghost? Has anyone a spare good original lying around?
Dominic Clancy

Dominic is "spot-on" Ted, I went ploughing in to answer your question without properly reading your question.
I overlooked the part that said you already had fitted relays.
Colyn
Colyn Firth

Can I ask why?

If your light switch is being supplied via the ignition switch, you won't have any parking lights. Is it not a legal requirement where you are? Certainly useful if you need to park somewhere which is unlit.
Dave O'Neill 2

Dominic and Colin, thank you

I could also add a relay for the running lights

Reason is I'm tired of killing the engine and leaving my lights turned on. I use them daytime to be seen. Protecting my battery from a rundown.

Driving in America has become a nonsensical
Hazard due to the obsession of "SUVs" and oversized pickup trucks. It's crazy out there! I'm dove grey and well below the door line of these monsters. I drive under the parking gate at my office garage. I do have a fifth brake light mounted on a magnet, a converted Hella rear fog light.

It's not our custom to leave lights on while parked at night, though fourway flashers are used for that purpose. Now there's an idea! Any comments for an easy add to the circuit?

Thanks all

Ted
Ted Persons

It wouldn't take much to add a simple buzzer circuit so that it sounded if the lights were on when you killed the ignition.
Dave O'Neill 2

For the lights left on issue, beginning with original non-modified wiring, install a piezoelectric buzzer between the ignition switch and light switch. The thing is also a diode. It will only buzz when lights are on and ignition is off. About $3 at RadioShack (if you can still find one open).

4-way flashers are also easy and pretty cheap. Install a Double-Pole Single-Throw relay (can also be double-throw) near the turn signal switch. It can even be taped to the side of the turn signal switch. Use the "F" switch to trigger the relay (since most MGA do not have fog lights). Wire the relay across the turn signal switch so both left and right turn signals are switched on at the same time. Also install Heavy Duty flasher unit (flashes one to six 21-wtt bubs). Magic 4-way flashers in hour for about $10.

If the HD flasher or electronic flasher unit only has two terminals (no "P" terminal), then for the 1600 car add two diodes from the two output terminals of the turn signal switch to the dash indicator lamp, For the 1500 car add two diodes from the relay unit terminals 2 and 6 to the light green wire originally on the flasher unit,

See here: http://mgaguru.com/mgtech/electric/et243.htm

If the "F" switch is being used for fog lights, then you need a SPST toggle switch to trigger the new SPST relay.

Alternately, you can use a DPST toggle switch wired to the turn signal switch, and you don't need the new relay.
barneymg

This thread was discussed between 07/08/2017 and 09/08/2017

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