Relays and Lights Opinions?

Ya know, it occurred to me today while starting to wire up another lightbar for one of the work trucks. I never use relays and all of my installs never have an issue.

Maybe I should use them, but honestly I never had an issue with anything I ever wired burning up or having an issue. I mean I typically use the largest wire possible, infact I have it setup with I believe 6 gauge wire as my power from the battery usually and then 10 or 12 gauge for the rest. I just wire the power to the switches and out the switches and Im done-no fuss no muss.

In the lightbar situation wiring in relays is a total and royal pita due to the limited room I have to work with as well.

Whatcha think..maybe I should bother this time? The ligthbar has 5 rotators, 8 flashers and 2 alley lights. Of course they wouldnt all be used at once but that is alot of draw.. I mean the last one I did still works 5 years later and all I did was use 6 gauge from the battery to fuse block, to the switches and out the switches again. Each switch was fused for 30 amps and never blew either.

Use a relay. You're running full current through the entire circuit which puts everything in danger of being overloaded. I have a feeling a switch would be the first to go as they don't usually like a lot of current through them. I also think 6g is overkill if the bar was wired properly. If a truck is big enough for a light bar and 6g it's big enough to fit a relay in. How many switches operate a light bar?

If this is for work you'd be money ahead doing it right and will get more kudos for doing it right than burning a truck or light bar. Looks up the specs for the bar and what the manufacture suggests for install.

Thats kinda what I been figuring mike, just all the extra wiring is annoying.

Understand Ive wired them in the past with no issues just using switches but I think this time Ill do it right. I mean 5x 55w rotators, 2x 55w alley lights and 8x 55 flashers I think might be a bit much. The other ones were much simpler with only 4 rotators, 4 flashers and 2 alleys.

Heres how I think Ill wire it up properly:
1. bring the power direct from the battery to a fuse block inside, this way I can easily distribute the power to the switches and other items if I want to.

2. Wire a + to the fuseblock to the relay with +

3. Make a common + 12v source for the switches

4. Make a common ground for all switches

5. Make a common ground for relays.

6. Wire it all up.

Im going to use this diagram to help me. http://www.classictruckshop.com/club...h/foglites.htm Although I wont be needing some things since the switches are lighted already.

Thoughts?

FWIW - My light bar pulls 45 amps will all the switches flipped. The previous owner used relays and housed them in a large plastic "project box" fed by 10 gauge wire from the battery. The control wire going into the cab and the switch box has a 9-pin d-submini connector on each end and some kind of CAN bus cable in between. While it's not used professionally or even every day, the previous owner is an electrical engineer.

Using relays shouldn't make it that much harder. Another incentive to do it the "right" way: are you paid hourly?

I found out my boss had some old switch boxes laying around that are ready to go, just plug and play. They have built in relays, switches and fuses.

You shouldn't need a relay as long as everything works right, but the same can be said about a fuse and I don't think anybody who knows the slightest thing about electricity would wire without a fuse. The idea behind a relay is to keep all the large wire, high current stuff outside the passenger compartment so that when there is a problem, like chaffing wires, the fire doesn't start in the passenger compartment. This will give you, the wife, fido, the baby strapped into the child seat, and grandma time to exit from the vehicle before it goes up in flames. It's the same reason to keep all the fuel lines out of the passenger compartment.

The bigger the wire, the worse it is, because it is capable of delivering more current than a small wire when it shorts. When a big wire shorts, it's not going to melt and will turn itself into a welding cable. That's why all the wires inside the cab are small. You'll want to keep your relay-to-switch wires small and your wires to the device sized correctly.

Your fuse block should be outside, near the battery.

Here's expats recent electrical fire.
http://www.toyota120.com/forum/showthread.php?t=21393

Thanks for the info steve. The wiring for these things needs to be quite large in some cases. Theres a 12V 3.4cfm compressor in there that we use 6 gauge wire from the battery wired to a 30amp circuit breaker and its about 20feet worth to bring it in. We tried smaller wire, it melted.

The switchbox I have now is wired with both fuses and relays so I should be ok. In the past I always fused things, thats just the smart way to do it regardless.

No, I think you misunderstood. You use large wire on one side of the relay and small wire on the other side of the relay. The circuit that goes from the battery to the relay to the device, should be large and sized correctly. This stays outside the cab. The circuit that goes from the battery to the switch to the relay, should use small wire and this is what goes inside the cab.

I understood that part, just that some of the wiring must be that large period or it will and has melted before. The compressors mounted inside the truck and need that thick a wire. I mean itself just for the switch on it uses 10 gauge.