Greetings one and all,
Wiring up switches for new fog and windshield lights (PIAA520,KC slim130) from relay to switch is it o.k. to use 16 gauge wire or do I need larger size wire?
Thanks in advance

 

From relay to switch you could go a lot smaller. I do not have my chart handy. But 16 awg is probably good for about 10 amps. 1 relay pulls less than an amp.

 

Since you're running from switch to power relay for the lights...it can be small, like 18g and usually no more than a 3A inline. Below will help you out with what sizes to use, etc.

Taken from another post off the local club forum:

First "know how" is AMPERAGE. The Amp draw will drive most of what you're installing for accessory ratings and setting inline fuse sizes.

To determine the amps of your accessory, you'll need to know the wattage which can be found on most product labeling/packaging. (IE - 55w Halogen Light). Then, multiply the total number of accessories by the wattage. (Four lights = 4 x 55w = 220). Once that has been determined, divide by the VOLTAGE of the system you are running off of, for MOST vehicles this is 12v.

By now it should look like: (4 x 55w) / 12v = 18.3a

For this application, you would need a switch rated at least to 20a and an inline fuse the same/as close to actual amperage.

NOW, what gauge wire to use...

Since amperage has been determined, you can use the table found here:
http://www.rbeelectronics.com/wtable.htm under WIRE GAUGE SELECTION TABLE. Find your amperage under the 12v column and follow the table over to the length of distance of your wire. This will tell you what gauge wire you need to safely run at minimum.

IF I were running the ablove 4 55w lights on 10' of wire I would need 16g wire.

OF COURSE, any manufacturer information should be followed, if available, but in the event you are running wires without complete guidance, this will provide a good base to begin from.

 

The switches I am using are the rocker 30a dorman. There are 3 connection points top earth(ground) Middle load-led bottom supply. from the relay #86 do I go to load or supply on switch? Then were do I hook up post not used? Tried looking at all the posts on how to do this but I am little lost
thanks

 

switch bottom goes to POS middle goes to relay switch top goes to ground. Sounds to me like a regular toggle with an LED that lights when switch is on right? On relay, run switch to pin 86, 30 to POS batt, 85 to ground, and 87 to the lights.

 

Correct so the bottom lug I would run a fused wire direct to Battery? middle to #86 0n relay?

 

bottom goes to pos, so you can go direct to batt (with in line fuse) sure. You can also go to a switched source if you want it to go off with the key. but the bottom goes to your batt source of whatever type and the middle goes to 86 on the relay. you got it.

 

I would'nt argue the fact that this method works. I'm sure that engineers use this formula every day on aircraft or spacecraft for weight reduction. But why use the bare minimum that you can get away with. For me, and based on my skills, If a circuit calls for 18 amps. It is going to get a #12 wire.

 

Thank you once again...Never to old to learn

 

anytime. You don't want to ask me about wire wire size though... cause I always go way over what I need for a job just to make sure there is no failures, resistance, or heat in a circuit. That formula is right on though, and a great way to calculate your minimum needs. I don't think you will have any problems with 16 gauge, but if it was me I would prolly use 12 to the lights and power/ground of relay, and just run the 16 for the switch power and switch to relay wiring.

I don't know how much wiring you have done in the past, but use good connectors and make sure they are attached securely. I like to take heat shrink over the ends of my connectors and cover from a little past where the wire goes into the connector to just past where the connector attaches. then I use elec. connector grease when I plug them up. Put your circuit breaker or fuse close to the battery and mount stuff solidly and up high. just my on wiring basics if you are new to it.