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Unread 10-29-2010, 07:09 AM   #1
YJhobby
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Re-wiring Headlights with relays: Electrical theory question

Hey guys,

I'm gathering parts and measuring wire runs for my headlight harness upgrade, and I realized that my planned location for the relays/fuses is about a 2.5ft wire run for one headlight, and about 7ft for the other headlight...

I'm upgrading from the stock YJ 18ga wire to 14ga aircraft grade wire, will the longer length of the one headlight actually make it more dim than the other headlight? I'm thinking of voltage drop over the longer length of wire.

I have a good feeling I am waaaaaaay overthinking this, and since the stock wiring was a longer run for one headlight also I should be fine.

Any input apprieciated!

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Unread 10-29-2010, 11:21 AM   #2
CJ258
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If you're upgrading to a heavier gauge wire you'll need to do something with the plugs going into the headlights. I didn't plan for that so I had to take them apart and reattach the heavier wire into the plugs.
I used dielectric grease on all the connections and you may need grommets shrink tube.
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Unread 10-29-2010, 12:11 PM   #3
gixxer1397
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Just curious on why you are doing this to begin with ?
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Unread 10-29-2010, 12:58 PM   #4
YJhobby
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I started this mod because I've been fixing alot of corrosion in the foglight/headlight connections. My jeep is a 1993, with 250,000 miles of highway driving in the state of Rhode Island.

Lets just say it has some age/corrosion issues...

I'm planning to replace all the headlight wiring with heavier gauge wire and a relay for each light funcion I have (Low beam, high beam, fog lights, windshield mounted KC's). The 18ga wiring is on the smaller size for the power a headlight puts out, and factor in the length of wire run, the resistance of bundled wires over a single wire, and practically 20years of use... It just gives me peace of mind and better lighting.

Oh... did I mention I have to wiggle the plugs at the headlight bulbs "just right" so they stay on... and then hitting a bump will make them go out. The connectors are pretty badly corroded, so yes they are getting replaced and will always have dielectric grease on them from here on out
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[QUOTE=SnowdogMarc] YJ's don't get stuck....they get temporarily impeeded in their forward progress.[/QUOTE]



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Unread 10-29-2010, 01:32 PM   #5
CJ7-Tim
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Gixxer, Jeep have notoriously weak headlight wire harnesses. Bigger wires means more light from the same headlamps. If you upgrade to an H4 headlamp you really will need larger headlight wires.

YJhobby, in theory, wire length does matter. Longer wire lengths increase the resistance in the circuit and resistance reduces current flow. You can Google a wire gauge calculator. If the difference was 2.5" and 50+" you might notice a difference, but a difference a of a few feet won't matter or be noticeable.
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Unread 10-29-2010, 05:11 PM   #6
CJ258
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When I rewired my CJ, the headlight wires were black for a foot back from the headlight plugs. And that was the 18 ga. OEM wire.
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Unread 10-29-2010, 05:56 PM   #7
SirGCal
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14 AWG would be fine for legal headlights (55/65w). The difference from one light to the other in additional wire is not going to cause that light to be dimmer. Don't worry about that. Not for just a few feet.
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Unread 10-30-2010, 06:14 AM   #8
YJhobby
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Quote:
Originally Posted by CJ7-Tim View Post
Gixxer, Jeep have notoriously weak headlight wire harnesses. Bigger wires means more light from the same headlamps. If you upgrade to an H4 headlamp you really will need larger headlight wires.

^ Sometimes I have a hard time explaining what I mean! (just ask my wife...) This is a huge reason I knew the headlight circuits needed help, along with my issues posted previously.

YJhobby, in theory, wire length does matter. Longer wire lengths increase the resistance in the circuit and resistance reduces current flow. You can Google a wire gauge calculator. If the difference was 2.5" and 50+" you might notice a difference, but a difference a of a few feet won't matter or be noticeable.
^ I used a calculator to determine that 14AWG wire was the correct to use... nice little charts if you know how to use them.

Quote:
Originally Posted by CJ258 View Post
When I rewired my CJ, the headlight wires were black for a foot back from the headlight plugs. And that was the 18 ga. OEM wire.
^ I fear the same issues will be present with my current wires too!

Quote:
Originally Posted by SirGCal View Post
14 AWG would be fine for legal headlights (55/65w). The difference from one light to the other in additional wire is not going to cause that light to be dimmer. Don't worry about that. Not for just a few feet.
^ This is the exact answer I was hoping to hear... ya know how sometimes just cause you know its right, it still doesn't seem completely correct until you have someone confirm it for you? Thanks


Thank you everyone!
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[QUOTE=SnowdogMarc] YJ's don't get stuck....they get temporarily impeeded in their forward progress.[/QUOTE]



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Unread 10-30-2010, 08:09 AM   #9
zooby
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When I made my relay harness, I used 12 gauge wire and ran the ground from each headlight straight to the core support. I don't know if the grounds are tied together or not on your model. I chose the larger wire because my h4's have 100 watt high beams. I'm sure 14 gauge would have worked but I like a little over kill.
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Unread 10-30-2010, 11:11 PM   #10
gixxer1397
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Never realized that the jeeps had a bad headlight harness, but its good to know. Like SirGCal said the 14Ga wire would be more then suffecient. Also I am not sure exactly how the jeeps work but I would say that the wire coming from your headlight switch goes to a relay somewhere in the jeep to trigger the headlights. good luck with your project and got me some reasons to look into the wiring of mine now, is this more prone on the TJ's or the YJ's ?
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Unread 11-01-2010, 05:45 AM   #11
YJhobby
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Quote:
Originally Posted by gixxer1397 View Post
Never realized that the jeeps had a bad headlight harness, but its good to know. Like SirGCal said the 14Ga wire would be more then suffecient. Also I am not sure exactly how the jeeps work but I would say that the wire coming from your headlight switch goes to a relay somewhere in the jeep to trigger the headlights. good luck with your project and got me some reasons to look into the wiring of mine now, is this more prone on the TJ's or the YJ's ?
This is actually part of the problem, I know for a fact the YJ does not have any relays that switch the power on/off, and I think the TJ is the same. Might have to verify that one...

18AWG wire direct from the switches in the cab to the headlights... I like knowing its fresh, non-corroded wiring of the proper size too.
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~Steve~

[QUOTE=SnowdogMarc] YJ's don't get stuck....they get temporarily impeeded in their forward progress.[/QUOTE]



I'm patiently waiting for the "foot-in-mouth" moment to end... but since I've posted, its not today
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Unread 11-02-2010, 06:08 PM   #12
neonhomer
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IIRC, companies like Painless make headlight relay harnesses. $170 though..... but they come prebuilt and pre-engineered....
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Unread 11-02-2010, 08:24 PM   #13
KJNewbs
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You can also search around for some posts from a guy named JeepHammer...he has some really nice diagrams that he made for all of this talk...where to put circuit breakers, talks about gauges and what to do when the wire gauge changes....I haven't done the upgrade yet, but I've been reading a lot and he seems to have the best input that I've found. I'm still going to keep looking - hoping to find a full write up with pictures and what not...i like pictures...haha...
cheers all.
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