mx5cartalk.com

I'm going to be wiring a set of foglamps up next week, now I have the wiring diagram, so I know what I need to hook into what, I just want to check that what I have in mind (from internet research) is safe in regard to wiring.

Info:
one pair of foglamps, 12volt, 55watt.
From what I read, this will draw just under 10amps.

Wiring I would be best to use 18gauge wiring? (apparently good to 15amps?)

Fuse I would probably get something between 10 and 15 amps (is it better to leave headroom for the lights? ie: go closer to 15amp fuse, or closer to 10amp?)

Relay I'm guessing just get whatever light relay they have since they all seem to be 15-30amp min.



Does this all sound correct? or have I just written a recipe for melted wiring and a constantly blowing fuse?

If you have a wiring diagram it should identify all components. Amps= watts/volts. 55W is pretty much standard. All the motor accessory places sell standard auto wire and terminals etc and its worth having a crimping hand tool and a selection of terminals. You will need a switch. The best advice is simply to go to the local auto elec and buy what you need from them and ask a question as needed. You can also buy universal wiring kits which provide all items required including an instruction sheet. Auto electrical wire is referred to as 3mm 4 mm etc and the number of strands and size is specified. You would be best to colour code the wire. Crimp terminals are colour coded to match the wire size and the crimp pliers has the colour displayed. PS do not use snap lock connectors - these are notoriously unreliable. When you crimp a terminal you can give the wire a pull to see that its crimped correctly.
Buying the right gear is something that you can use again for another job esp if you a car fiddler.

Unfortunately the diagram only showed the wiring layout and the components, it didn't give specifics as to the sizing of each component.

For the switch I'll get one from a wrecking yard, it will be suitable for a car (having come from one) and should fit neatly into one of the blanks on the dash.


Thanks for the tip re: connectors, I'll keep it in mind when I buy all the bits and pieces.

I would go one further and solder your joints and heat shrink them with a turn of tape at each end of the heat shrink.

Nic,
A 30 amp relay will do, install a 15 amp in-line fuse on both power sources, primary and from switch (belts and braces) and use the fattest cable that you can get fittings for as it will provide less resistance which equals less heat as well as less voltage drop and therefore more light and less stress on your charge and running system.
Greg.

I was going to suggest not soldering the joints. Many end up with a worse connection ie bad soldering - crimping is- using the right components reliable. PS do not use the fattest cable that is incorrect- you use the right cable- you are not fitting a starter motor.

Another quick question that has entered my mind.

Main power for the lights. The diagram says battery, but since the MX5 battery is in the boot, rather than run a wire all the way back there, and I safe to instead find power elsewhere in the engine bay? (for example, take power from the fusebox?)

Nic,
You could take your primary power source from the starter motor.
Greg.

Mr Morlock wrote:I was going to suggest not soldering the joints. Many end up with a worse connection ie bad soldering - crimping is- using the right components reliable. PS do not use the fattest cable that is incorrect- you use the right cable- you are not fitting a starter motor.

Read the entire response Mr M .
Greg.

Awesome.

Thanks Greg.

Go the solder, happy to chat offline about the technique.

I've built a number of driving light looms and a couple of full car looms for my rally cars and never had a problem with a soldered joint. Just lots of heat into the joint and if the solder spreads well and looks shiny you're on the money.

Cheers

Mark

Also +1 to Greg's idea of the starter motor

be careful with battery disconnection ie some vehicles require code for radio but probably wise if you are removing the power lead to attach a terminal to the post on the starter motor to use as a power source. Solder is simply an old fashioned and often unstable process- far too operator dependent. Crimping terminals are readily available with insulation included and right size wire with right size terminal and a crimping tool is likely to give a reliable result- shrink tube is easy to apply.

Mr Morlock wrote:be careful with battery disconnection ie some vehicles require code for radio but probably wise if you are removing the power lead to attach a terminal to the post on the starter motor to use as a power source. Solder is simply an old fashioned and often unstable process- far too operator dependent. Crimping terminals are readily available with insulation included and right size wire with right size terminal and a crimping tool is likely to give a reliable result- shrink tube is easy to apply.

Mr M,
I agree, solder is an old form, an art form in fact (Dry joints etc) If Nic seeks out some 4mm spade lugs to suit his application and tells the retailer exactly............I'm tired now.
NIc,
Have a chat with Droo if you see him on Thursday and Mate, if it looks like too much PM me.
Greg.
P.S. I am hoping to be in Smellbourne on the 21st Sept, but Hey! Pam can do it .
Best.
Greg.

Getting there.
I didn't finish the job on the weekend, I ran out of wire, and also it started raining.


Regardless, it's mostly done except for a few slightly annoying bits.

I need a bulb holder for starters, I'm missing one and the wreckers didn't have one (I'll try some other yards when I get a chance)
as for the wiring part, I've attached the relay, and I've run most of the wires through the engine bay neatly.

The only thing left now is for me to run the wires into the cabin to attach to the switch.



Speaking of which, I have a question.
As it stands I'm going to take my trigger power from the parking lamp wires (directly behind the headlight then run the wire up to the switch, then back out to the relay)

I was originally going to try and get my trigger from the dash somewhere, but couldn't seem to find any accessible wires apart from the ones on the dimmer wheel.


The dimmer wheel has 3 terminals, a black, a red/black, and a white/red.

When I hooked the multimetre up to white/red and black I got about 3v when the lights were turned on, 0 with no lights.
When I hooked to red/black and black I got about 14-16volts with the lights on, and 0 without.

The problem was that after about 30secs hooked to red/black and black the multimetre wires started to smoke....... what the hell happened here?


I know black would be earth.
Red/black I took to be positive, and white I had no idea.

Why did the wires start to smoke? I'm guessing this means I shorted something, but how can it be a short?

My electrical knowledge is about zero, I can't even fathom the difference between a short circuit, and a normal one.

A normal circuit would be say a battery, with the + to a light bulb, and the - to the other terminal on the bulb, correct?
Whereas a short circuit would be placing a wire between the two bulb terminals. But how is it a short? the power would still flow from positive to negative? why is pos to neg bad with wire, but good with a globe?


Another example I did, I bought a tap fuse to make it easy for me to take a trigger from the under-dash fusebox.
I plugged in the tap fuse, put the positive of the multimetre onto the tap terminal, then the other onto the door hinge to ground. The result was the fuse blew instantly.

Again, how does this work? electricity goes from positive to negative, if I want to test for power at a point I can't just put the positive terminal on, the multimetre shows nothing.





I've worked out the wiring in the car, I can get that done, it's more for my understanding of the concepts of why it works.

The concepts of a normal circuit and a short circuit seem to contradict each other.


edit:
http://www.atbatt.com/blog/28.asp

So in this case, a wire from pos to neg = short
But if there is anything in between that has some electrical resistance it's not a short? (so it works by positive giving out X units of electricity, and negative receiveing <X units back?)

In that case, how does a multimetre work? does it simply work by shorting out a circuit and showing the voltage on the screen?