Basic wiring help please

[Paul Thomas]

Ok, i am not completely inept when it comes to wiring, but i am close. I bought this Hella switch for my driving light project.

Do i run a fused 12 volt wire into one side of the switch, out the other side, and to the relay? What amp fuse,15?

If so, how do i power the bulb? (bottom spade)

What gauge wire should use and should I split it off of the stereo or some other keyed power source?

Paul

[Paul Thomas]

screwed up the pic.

[randywebb]

looks like the paper it sits on tells you what to do?

primer: electricity has to flow in a loop -- it has to get back to where it started.

in your car there is only one wire (called the hot wire) that runs in the electrical circuit (circuit implies loop, right?) because the other 'side' of the loop is the body of the car itself - the Ground

the ground is drawn by convention as several short horizontal lines that are centered over a vertical line - every time you see that it means a ground

in German cars solid brown wires almost always mean they go to a ground point on the body

gt a piece of paper and draw a box on it with 2 lines, one gets a minus sign and goes to ground; the other gets +12 VDC written next to it (that is the battery - the source of electrons that will move in the wires) - it runs to a fuse, and then the switch, and then to the bulb; the bulb is a curly thing (filament) and the other side of it gets a ground symbol -- that's how the electrons get back to the battery

how's that? help at all?
post the diagram they gave you and a more specific question if not.

if this did make sense then we will just skip to Quantum tunneling in PNP junctions.

[Paul Thomas]

Thanks Randy that was impressive. I did post a picture of the diagram and i think i asked four specific questions. If I was clear on what to do from looking at the diagram I wouldn't have posted this in first place would I? Here are the questions for anyone who actually wants to help.

1. How to wire the switch.
2. What amp fuse to use.
3. How to power the bulb in the switch.
4. What gauge wire to use.

Paul

[randywebb]

can't see much of the diagram...

#2 & #4 both depend on the size bulb used

[Early_S_Man]

Paul,

How many bulbs and what Wattage are you using in the driving light package?

The general rule-of-thumb is to fuse at twice the nominal load. Two 100 Watt bulbs from a single relay would be fused at 30 Amps ... because the normal load is 14.28 Amps. Dual relays [one per lamp for redundancy] would be each fused at 15 Amps.

That Hella lighted switch requires '+' power, and'-' ground connection for the bulb, and the output terminal is '+' power ... which should go to a relay coil. When you pull out the switch it powers the bulb and switches '+' power to the output terminal.

[Walt Fricke]

Well, you also said you are using a relay. The purpose of the relay is to allow a small current (=smaller wire and, if used, smaller fuse) to send a larger current to the actual device (in this case, a pair of fog light bulbs I suppose).

That poses a question: do you fuse the control circuit, the power circuit, or both. I don't know what the consensus of EEs is. I tend to want a fuse to protect just about everything, in case a wire creates a short, so I'd fuse the control circuit positive wire at or close to the fuse box (or the stereo switched power, if that is located conveniently or is simply one you know you can locate), just in case it gets shorted. Porsche grabs it from a headlamp circuit, I think (partly so you can't have the high beams and the fogs on at the same time, but I forget some of this).

And I'd do the same for the power circuit which runs from the fuse box or somewhere (it could come direct from the battery positive, for that matter) to the relay.

How big? Well, you could use a pretty small fuse - 8 amps would be more than enough - for the switch circuit. As to wire size, look at the wires to the instrument lights. Those are plenty big enough for this task, and for the indicator light bulb as well.

The power circuit? Look at the wires which go to the headlamps. Those are thought to be marginal for their job, but should be fine for your fog lights. Get some that size. And fuses? Well, you could experiment - put in an 8 and see if it blows. A 16 ought to be enough, I'm wildly guessing.

Want to be more accurate? Well, you can can pretty easily calculate the power draw. Somewhere you can find how many watts your fog light bulbs are rated for. Let's say each says 60 watts, so you have 120 watts. At 12 volts, that means the pair are drawing 10 amps. The wires will draw a bit more all on their own, as they have some resistance, but you'd be fine with a 16 amp fuse in this example.

Hooking up your indicator light bulb? Simple. The switch has an in and an out. Run a second wire from the out side (the one that heads off to the relay) to the bulb. I'd crimp that wire into the same connector as the wire to the relay, though it would be quite short. It looks like the switch body is grounded, but if you find your bulb doesn't work, connect some metal part of the switch to a ground to see if that makes it come on and then improve the switch grounding.

Some of this I think you can, after Randy's help, dope out from the diagram that came with all this. I deduce from it that the wire to the switch with the circle with an X inside indicates a switched power source. And there is no particular reason to choose one or the other of the two top spade lugs for the "in" side of the switch, which is just a single pole single throw (on or off) switch I imagine. Whichever one you chose is the in, the other the out. It only depends on where the wires come from or go.

If no relay is involved, you just need biggish wire for everything, but you still want the fuse as close to the source of 12V+ as you can reasonable get it. Blown fuses are not a big deal, but fried melted wires from a short can be, and at a minimum often melt and mess up more important wires.

I don't have giant stereos, so the wires to my radios are pretty puny. Not big enough at all to power fog lights (though they should handle relays and indicators). If there is no relay, I'd not start by thinking of stereos.

Maybe some real wire guy will check in with wire gauges and actual fog lamp wattages and such. You may want to buy wires at a store using specs instead of just looking in your spare wire box for something long enough and thick enough by eyeball as I would. Porsche wires are specified by their thickness in millimeters, not in the "gauges" that US wires tend to come in.

Walt

[911pcars]

"I bought this Hella switch for my driving light project. Do i run a fused 12 volt wire into one side of the switch, out the other side, and to the relay?"

If that switch diagram was all they provided, it's mostly not helpful. They show a 15A fuse connection. That's probably for a direct-connection to the driving lights. Use a relay, just to decrease the length of the circuit and to reduce voltage drop resulting in reduced light output.

Connect a fused source to the switch then to terminal 86 of a standard 1M-1B Bosch relay, then to ground via terminal 85. This is the control side. Theoretically, the switch can be on any side of the relay control circuit.



"What amp fuse,15?"
Two fuses total: 5A or less on the control side, 15A should be sufficient for two 75 watt bulbs on the power side.

For the power circuit; from source voltage, create a circuit from the 15A fuse to terminal 30, then from term. 87 to a branch circuit to each driving light, then to ground. 87a isn't used.

"If so, how do i power the bulb? (bottom spade)?"

Depends on how the switch is designed. With no battery connected, check the switch continuity with an ohmmeter. You want to create a path from source to switch bulb to ground with the switch ON and an open circuit with the switch in the OFF position. In some switches, the source connection to the switch bulb is internal. Thus the bulb terminal should be connected directly to ground. Verify your findings on the bench with a battery and test leads before permanently connecting, then draw your planned circuit on paper so you have an installation map to follow.

"What gauge wire should use and should I split it off of the stereo or some other keyed power source?"

On the control side, 14-16 ga. depending on the bulb wattage and length of circuit. You can connect to any fused circuit as long as the total circuit current doesn't exceed the fuse rating. Your preference whether you want this circuit "hot" via the ignition switch or not (i.e. radio circuit source voltage is activated by the ignition switch; the headlight circuit source voltage is unswitched).

On the power side (feeding driving lights), use 12-14 ga. - thicker wire for higher wattage and longer circuit length. I suggest a dedicated fuse for this circuit at the fuse box (non-sunroof cars usually have an extra fuse position for the SR motor) or connect a separate inline fuse branched from the battery pos. post or other large gauge wire on the unfused side of the fuse box.

Maybe more info than you need. Hope this helps.
Sherwood
http://members.rennlist.org/911pcars

[Paul Thomas]

Thanks guys, great help, i'll have it wired in no time.

Paul

[randywebb]

be sure to clean up any grounds you find -- use detergent, then soak in vinegar until shiny -- put a wet cotton ball over areas on the chassis