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MG Midget and Sprite Technical - electrics

hi all,
i want to fit a spot light a fog light and another horn.im running a dynamo. i want all 3 to work seperately.or fog and spot together, on the fuse box i have 1 spare constant live and 1 switched. can i take 1 live and link all 3 switches with the live or what is the way to do it. what is the best and safest.
thanks bob.
bob taylor

Hmmm .....

Depends on the quality of fire extinguisher you have

If it where me just off hand without reserching this ... incorperate a relay between the fuse box and the lights themselves

I think id even go as far as a sperate fuse box with a 20 amp inline fuse directly to the battery

Be sure to use a fatter gauge wire to the spot and fog lights...im going to take a pure guess and say 18-20 gauge wire at the minume

But if you have a helo fire suppression system... then yeah, wire that monster directly into that 40 year old wiring birds nest ....hahahah, just keep a package of hotdogs available

Prop
Prop and the Blackhole Midget

Hi Bob, not a direct answer as my electrical knowledge isn't great, but when I rewired my car (2 fuse box) I wired in a later style 4 fuse unit to fuse my dip, main and spot lights separately with relays and I still have one spare.

HTH
Mark
Mark Whitmore

I would connect the constant live to the accesories through 3 relays, with your dashboard switches etc triggering the relays.

That way your ignition switch is carrying less current.
Growler

Here is what I did:

Power them all from a new wire, run from the Brown terminal on the regulator. Provide your own fuse on this new wire. Use this power supply for all three relays.

Use one relay to switch the high beams, and add the one driving light to this as well, so that you don't need to add any switches, and doing it this way you use a relay to protect your existing high beam switch.

Use one relay to switch the fog light. If your midget has the MGB column mounted wiper stalk (in the US it was used from 8/'72, but I think it was later in UK), there is a switch for the MGB overdrive that is operated when you push that stalk forward. Use that switch to control your fog light.

Use one relay for the horns. Note that the horns operate by a broken ground, so that relay is wired differently than the other two which operate by switched power supply instead.

The switched high beam wire is blue/white.
The "overdrive" wire in the RH stalk is yellow.
The horn switch wire is purple/black.

The total watts for horns (the big Lucas wind tone ones which draw over 2A), 50W high beams and two 50W aux lights comes out to approximately 17A. I recommend you use 44 wire (12 gauge) for the power supply (good up to 25A), and a 17A fuse on that, and use 28 wire (14 gauge) for each of the circuits (good for 17A). Of course, you can use larger wire if it is more convenient for you, but those would be the minimum safe gauge. If you are concerned about a 17A fuse being enough, then use a separate 17A fuse on each of the wires going to the individual relays.


I agree with the others, do not try to run all of this off of any existing circuit in your car (because you will overload it), and use relays to protect your switches.


To hook up a relay, connect the switched wire to #30, connect #87 to ground. Connect your dedicated power supply to #86, and connect the lamp to #85.
In the case of the horn, instead connect the power supply to #86, and connect #85 to the horn switch in the center of the steering wheel. Connect the purple/black wire from the horns to terminal #30, and connect #87 to ground.


Hope this helps,
Norm
Norm Kerr

Gday Bob
Norm's advice is excellent, see the image attached to show how to wire the relays HTH Cheers Rod


R W Bowers

What the freak norm....

ive heard of childrens "paint by numbers an elvis on black velvet" but ive never come across (electric by numbers) before

hahahaha

Seriously... that was a very good write up on how to do it, im very impressed. Thank you for pisting that.... im making a copy of that for my MG file notes

Prop
Prop and the Blackhole Midget

thank you gents most helpful.
regards bob.
bob taylor

This thread was discussed between 21/08/2013 and 22/08/2013

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