protegeboy78

I want to hook a couple of interior lights into seperate switches, but i'm not sure how to power them, can i run a wire from the batterie directly for power? or do i have to put in a fuse or what? anyone have any idea?

derrick1623

run the power from the battery, ground it somewhere, then run the wire to power what ever accessory

derrick1623

on the negative terminal?, but my switch doesn't even touch the negative terminal, and what size fuse should i put in?

mazdaspeedwest

if you want the lights to be able to turn on at any time, draw power from the battery, with a 10 amp fuse depending on the lights tho. If you want them on only when the key is on, use ignition or switched power with the same fuse, either way, put the fuse a few inches from where power is taken from.

you may want to have the switches flip relays rather than a direct hit to the lights, that way, you don't have to worry about the switches pulling all the power, the relays take the heat.

but very simply, power to one pin of the switch, light to the other, then ground the other wire of the light.

JJB

a fuse on the negative lead is going to do very little...even if you break the circuit by popping the fuse (which means something has gone wrong) there are many areas that can now provide an alternate path. This is because the whole car frame (and most metal bits on it) is a negative return to the battery thanks to that heavy cable that bolts from the battery to the frame (notice that there is no fuse there).

What you do need is a fuse on the positive leg of the circuit (just like everything else in the car). Also, if you are running a cable directly from the battery you want it to be as close to the source (battery) as possible? Why... say that the cable gets abraded somehow... now it shorts to the frame... you have a dead short to the frame, the battery delivers many amps, things get hot, possible fire. If the cable is very small it usually melts and goes up in smoke... if it is nice and heavy it gets really hot and causes other things to go up in smoke.

Fuse the circuit on the positive and do it close to the battery.

Liv2ride21

Ok, a few friends of mine are helping me put some lights in my car, since i've never done it. They are planning on just wiring them to a switch and then to the back of the cigarette lighter for power. Is this a good idea??

In terms of fuses/protection from shorts what else should we do?

protegeboy78

I just took off the front part of my dash to paint it and discovered that even though i don't have the dash clock i have the wiring that plugs into the clock. Would it be a good idea to wire those wires into the switch box to power the switchs/lights i am installing? That wayi don't need to run wires to the battery, don't need additional fuses and such.

JJB

The cigarette lighter usually has a pretty big fuse on it (15 or 20A). Depending on your application that might be enough protection. If the lights do not draw a lot of current and you are feeding it with a small aguge wire then you might want to install an in-line fuse on the positive leg right after where they tap into the cigaretter lighter. That way if something goes wrong it will pop there and keep that little wire from causing problems.

It all depends on how careful you want to be (feel a need to be).

JJB

I would try to find out what else is on the circuit that the clock is on. Usually something like that will be on a shared circuit with other things. If you think that the circuit can provide sufficient current (the wires are heavy enough, and the fuse that feeds them is sufficient) for your application it might not be a bad place to tap off. In this application I would still add an in-line fuse on the positive side right before the switch, so that if something does go wrong it does not pop the fuse in the fuse box and shut down the other things on the circuit.

Can you tell that I am somewhat retentive when it comes to wiring?

randallb

In past cars I have often had good luck by finding a "spare" or unused accessory circuit in the fuse box. Get a wiring diagram if possible, or look at the fuse box cover for a guide (on some cars). If you get lucky, then you won't have to remember where you hid that inline fuse a couple years ago when something blows!

If no fuse available, use a crimp wire tap (Radio Shack, etc.) to tie into an existing circuit with sufficient capacity.

In any case, for low amperage lights use at least #16 stranded wire (lower number is higher capacity), use crimp connectors or solder w/heatshrink tube, and tie your wires (that's use those nylon wire ties or similar).

Yeah, I'm kinda **** about wiring too!

JDMstuff

The clock is usually tied into the backup fuse for the ECU. I would try to find a thicker wire from the ignition harness. It's usually fairly thick gauge wire and should be able to handle the current you need. If all else fails, just run a 10 gauge wire directly from the battery into a distribution block (doesn't have to be the ones for a car stereo system-radio shack sells some inexpensive ones.) and plug in whatever switches you want. BTW, there isn't much as far as lighting is concerned inside the car, what are you trying to add a switch to? If you're trying to hook up a couple of NEON tubes, you should run them off of the battery from a distribution block. Make sure you add a fuse between the battery and the block, you don't want to burn a trace into your carpet.

protegeboy78

I want to put one small red light (about the size of a small rubber bouncy ball) above the gas pedal and one same place on the passenger side since i have no light there at all, and i have a rope light inside the car. None of those lights draw much power.

vsykes

Hey,

First thing, DO NOT LISTEN TO Protege Menace. I have never heard of fusing the ground side, simply since you shouldn't have a wire connected directly to the ground terminal on the battery. All you do is this:

1. Find the primary power connection under the hood. (where the positive terminal runs to from the battery under the hood. There should be a Terminal with a nut you can loosen.)

2. Loosen the bolt and put in the wire that is to go to the switch.

3. I would advise putting a inline fuse under the hood

4. the wire has to be run through the fire wall, usally you can find a pre-existing hole in the fire wall with a grmmet covering it. I recomment lots of wire ties so the wire is out of the way under the hood and dash.

5. Connect that wire to the switch.

6. The second wire from the switch goes to the light.

7. The ground from the light just has to connect to any metal part of the car. I usally just find a nut near buy and loosen it, then wrap the wire around it and tighten the nut.

JJB

Sorry if this is going to ruffle some feathers.

That is NOT how you are supposed to do it. Take a look at ALL the wiring that is in your car (not your wiring, the one done at the factory). You will notice that the fuses are all on the positive side of the battery. You can see that there is a main fuse under the hood very close to the battery sitting on the positive leg of things. I am not sure about the proteges, but the only thing that is not fused in most cases is the starter motor.

Now... as I said in my previous post. Why fuse the positive as close to the source as possible?

Let's just say that you did not fuse it on the positive but fused it on the negative.

1. run wire into the car through the firewall (use a heavy gauge) and then run it to something in the trunk (an amp?)
2. run the ground wire back the battery (we need to do this as we need to put the fuse over there).
3. Or, instead of that let's just bolt it to the chassis right where the amp is. We leave the fuse on the wire that bolts to the chassis
4. everything turns on and off as we expected. The circuit it complete and nothing is wrong.
5. a few months go by (and since you forgot to put a grommet where you drilled to get through the firewall) the wire has been getting abraded due to friction.
6. the insulation breaks
7. the wire shorts out to the chassis.
8. now the length of wire between the amp and the front of the car where it is shorting are both at the same potential.. no current flows, the fuse never sees the current draw... but the length of wire from the postive of the battery (where we took power) to the frame of the car (negative as it is connected via that really heavy wire in the engine compartment) is at a potential difference. Current begins to flow. As there is nothing really dissipating the current (the nice heavy cable is a dead short) the battery starts to dump some severe amperage into the cable. Now the battery is getting hot, but so is the cable... it starts to get really really hot... we are talking a lot of amps being delivered by the battery here so the ohmic resistance in the cable does disipate some of the energy as heat. The insulation melts and the wire is now really hot and where ever it is touching things are going to start to burn. Of course the cable (if small enough) will eventually melt... but a nice heavy cable will just cause the battery to get hot enough where fire/explosion might be an issue.

OK... now let's try this again, fusing the positive side.

1. run a heavy cable from the positive a short distance to an in-line fuse
2. run a cable from the otherside of the fuse through the firewall to the trunk
3. hook up the load (amp)
4. hook ground via a cable to the battery, or hook it to the chassis
5. - 7. are the same
8. we once again have a situation where the length of cable running back from the firewall is now at the same potential as the negative of the battery... no current flows there
9. now we look at the positive side... the nice heavy wire starts to pull from the battery... the battery delivers a lot of current... we exceed the rated amperage of the fuse... it opens. Now the circuit is open and current no longer flows. No heat, no more damage, no fire.


So... where does the fuse go? Pick your scenario.

-JJB (B.S.E.E.)

JJB

Actually both scenarios can happen, it just depends on what leg you put the fuse in. In any case as you have seen the fuse should be in the positive leg and as close to the power source (battery) as possible.