keep blowing lighting fuses :( - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 09-06-2008
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keep blowing lighting fuses :(

Hey guys I got myself a lighting predicament with my new lighting i bought for my ranger. so I'm sharing it with you all

Anyways I bought a set of aftermarket headlamps with projector lights and while the main headlight beams work fine I keep blowing fuses in the wiring harness that came for the projector part of the new headlamps. This is something I figured was going to happen as the wiring looked pretty puny. I believe its 18AWG between the battery and the 12v 30amp relay with a 15amp atc fuse.


I have the two projectors with H3 lamps in them and then two H3 driving lamps spliced into that harness. Interestingly everything was working fine until i replaced the cheapo oem 55w bulbs with H3 Silverstars(65w) then the fuses started blowing.

Now I'm trying to decide what to do about it. I'm planing on rewiring the harness with thicker wires and upgrading to a 25amp fuse. However I'm still not sure if that would be enough. I cant seem to find any specs on the amp draw for the silver star h3 bulbs.

As for wire i will be using 12AWG wire and I keep finding conflicting reports on how many amps it can safely carry. I assume it can handle it because I've been to every different auto parts stores around town and they all had replacement fuse holders that support up to 30amp fuses with wire no larger then 12AWG. Yet the packaging on 12AWG wire rolls state up to 22amps

The second option for myself would to replace my projectors with HIDs that come with its own harness then use the current harness with its relay for my driving lights only. I would then have to run the switch wires through both relays so they both come on. If i do HIDs I'm not sure color temp to get. I'm going to be putting 4300k HID'S in my main headlamp beams shortly anyways. I'm thinking something with a slight tent of blue would look pretty cool in the projectors if you looked at them directly but I think it might look strange from a driving view on the road if its too blue. So I'm undecided between 6000k or 8000ks for my projectors.

Also if going with more HIDs i have no idea were i would stick 4 balasts in my 4.0 V6 engine compartment along with the wiring for three relays(main headlamp, projectors, driving lights).


So many gotchas and decisions Feel free to help me make sense of this mess haha.

Oh yeah here's a picture of my lights on my truck:

Last edited by crucialcolin; 09-06-2008 at 04:45 AM.
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Old 09-06-2008
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You're fine with 12g wire for that. But either something is shorted to ground or your fuses are no the right rating.
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Old 09-06-2008
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4 55 watt lamps = ~18 amps
4 65 watt lamps = ~21 amps
That is assuming a system voltage of 12.5 volts.

As for the current capacity of the wire:
12 ga stranded will carry 22 amps
12 ga solid wire will carry 25 , but you don't want to use solid wire in a vehicle as the vibration will eventually break it.
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Old 09-06-2008
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The amps a wire can safety carry depends on how long it is. You can't just say that a certain gauge can carry a certain number of amps and be done with it. For 12 gauge wire:

50 Amps - 4 feet
40 Amps - 7 feet
30 Amps - 10 feet
25 Amps - 12 feet
20 Amps - 15 feet
15 Amps - 20 feet
10 Amps - 30 feet
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Old 09-06-2008
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Wow , I don't know where you got that info from , but the national electrical code says different.
The diameter of a wire is what determins current carrying capacity.
Length becomes an issue of resistance . Longer wire runs equate to more voltage drop (even copper wire has some resistance to current flow).

12 ga wire will handle 50 amps , but not for an extended amount of time.A couple minuites maybe before the heat in the wire begins to melt the insulation.

But , what do I know. I've only been involved with electricity/electronics for 30 years.
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Old 09-06-2008
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Quote:
Originally Posted by OTRtech View Post
Wow , I don't know where you got that info from , but the national electrical code says different.
The diameter of a wire is what determins current carrying capacity.
Length becomes an issue of resistance . Longer wire runs equate to more voltage drop (even copper wire has some resistance to current flow).

12 ga wire will handle 50 amps , but not for an extended amount of time.A couple minuites maybe before the heat in the wire begins to melt the insulation.
Right. I know. But I would consider the wire insulation melting and catching the truck on fire to be exceeding its capacity regardless of how many amps the national electric code says 12 gauge wire can physically handle. If it is on fire, who cares if it can still carry the load. And yes, it can certainly handle 50 amps at short lengths because the resistance is low enough. It is done all the time. This isn't NEC home wiring. It is automotive and its not the same.
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Old 09-06-2008
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Whoops double post
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Old 09-06-2008
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Def dont want any fires

Anyways I'm thinking about going the route of installing a secondary relay so both the projectors and driving lights get their own hookup to the battery and fuses. I'll then have to run the switch through both relays.

I noticed today the projectors get way too hot with the silvania bulbs. So hot that I put my finger on the outside of the plastic housing I actually burned myself :( there's no way in heck those can sustain 65w bulbs like the silverstars and now I see why they came with 35w bulbs.

It looks like my only option with the projectors is to go to 35w HIDs if i want a decent light output from them. Now I have to decided on color lol.
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