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Driving Light Wiring Q&A
Topic Started: Mar 31 2015, 08:38 PM (710 Views)
Thart10


What is wrong with this arrangement? Crude drawing but it's that simple.
Posted Image

I've used this on many cars with a lot of Plastic in the Bumper area, rather than fish out a connection point on the Fuse box. Lately, the 20 Amp switches are getting HOT on both cars, to the point they Melt.
Something happened on the Geo last week. All the lights dimmed, Battery Light Came On and engine ran poorly. Switched OFF the Driving Lights and things returned to NORML
I added a Relay to the Toyota, but before I do that to the Geo, I want to be sure I'm not just moving a Fire Ignition source under the hood where I can't see it smoking until it's too late.
If something is "wrong", why doesn't it Blow the 10 A Fuse before melting the 20 A switches?

I'm thinking this system is getting the Full Battery Amperage and the Full Alternator Voltage, but using only the 12 Volts/10 Amps it was designed for.
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Good bye


They are probably only 2 amp switches in reality. LOL
I always use a relay under the hood with a fuse as close to the power source as possible and switch the negative, so if I have a short somewhere either the fuse blows or the lights just turn on.
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Metromightymouse
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Powdercoat Wizard

me and my metro
Mar 31 2015, 11:37 PM
They are probably only 2 amp switches in reality. LOL
I always use a relay under the hood with a fuse as close to the power source as possible and switch the negative, so if I have a short somewhere either the fuse blows or the lights just turn on.
Yep, you are overloading the switch, either because they are low quality, they are 20 amp ac rated, or the contacts are oxidized and adding resistance to the circuit which creates heat and damages things further (more oxidation/melting/etc). A relay is always preferred in lighting circuits, takes the load off the contacts in the switch and a little oxidation doesn't create a lot of heat and a cascade of issues/failures, including a fire. :bananaburn
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Thart10


The switches came from AutoZone & Advance, so you'd think they'd be rated for DC. Their Light kits Instructions don't show a Relay in the circuit. Guess they plan on you coming back often for New switches. :smackface .
I'll bet if I put the Fuse on the other side of the switch, it will blow first. Right now the 20 A Switch is taking all the Volts/Amps the Lights don't use, before it reaches the 10A Fuse.
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Metromightymouse
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Thart10
Apr 2 2015, 03:41 AM
The switches came from AutoZone & Advance, so you'd think they'd be rated for DC. Their Light kits Instructions don't show a Relay in the circuit. Guess they plan on you coming back often for New switches. :smackface .
I'll bet if I put the Fuse on the other side of the switch, it will blow first. Right now the 20 A Switch is taking all the Volts/Amps the Lights don't use, before it reaches the 10A Fuse.
It's just low cost parts. The switch melts because of heat, heat is caused by resistance. The switch is just supposed to be contacts with little to no resistance. If the materials are not manufactured correctly or the circuit is carrying more current than they are designed for then heat will accelerate the degradation of the contacts in the switch, or any other weak link for that matter. More resistance results in more heat and that causes more corrosion and more resistance. You can see how this quickly gets out of hand. Including a relay costs them profit and if the original design will last longer than the warranty they don't worry about it. When you buy a light kit, the inclusion of a relay is one indication of better quality than the low price leader.
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DesmondGhostRider
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I always use a relay. Had some trouble with lights overheating in the past that caused all the wiring to melt :( Granted it was 2 hella flood lights, but still.

Edit: I'd also recommend putting the relays inside the cab of the car where there's less water.
Edited by DesmondGhostRider, Apr 2 2015, 10:40 AM.
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