headlight wiring, relays
Thread Starter
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Hotshot
Joined: Nov 2000
Posts: 11,591
Likes: 14
From: Pflugerville, tx
headlight wiring, relays
As I start to work the wiring harness, I am wondering if I want to direct wire the headlights, or use relays to power them.
anyone made that decision? I am using the EZwire harness, and the Ron Francis ignition switch, rated at 40amps. I want to use the H4 halogen bulbs. On my sons Miata and his 66 Chevy pickup before that the ignition switch couldn't take the power load, so we used relays instead.
Sam
anyone made that decision? I am using the EZwire harness, and the Ron Francis ignition switch, rated at 40amps. I want to use the H4 halogen bulbs. On my sons Miata and his 66 Chevy pickup before that the ignition switch couldn't take the power load, so we used relays instead.
Sam
Fleet Owner
Joined: Jul 2004
Posts: 27,294
Likes: 1,055
From: NM
On Bonus Built trucks at least, and most cars, the lights aren't powered thru the ignition switch. You couldn't use the parking lights unless the ignition were on (like if you're parked). They are usually on a circuit breaker direct off the battery.
Assuming you're running 12v, lights should be less than 15 amps total. I just don't see a lot of need for relays on our trucks, and it would add a lot of wire, since they should be right up near the headlights for max benefit. The halogens like full voltage, so just use generous wire size to them.
Assuming you're running 12v, lights should be less than 15 amps total. I just don't see a lot of need for relays on our trucks, and it would add a lot of wire, since they should be right up near the headlights for max benefit. The halogens like full voltage, so just use generous wire size to them.
Thread Starter
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Hotshot
Joined: Nov 2000
Posts: 11,591
Likes: 14
From: Pflugerville, tx
thanks. I've got examples. It was more how many of us have done this with new harnesses.
just gotta find a nice hidden place for the relays..
Sam
just gotta find a nice hidden place for the relays..
Sam
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Senior User
Joined: Mar 2002
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From: MOYOCK NC
i mounted mine on a metal plate that was bolted under my fuse panel i tucked mine under the dash almost straight above the dimmer switch
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Laughing Gas
Joined: Feb 2002
Posts: 932
Likes: 9
From: DFW, TX
Sam,
Mark another vote for "relays!" I've used them on several vehicles, with and without headlight upgrades. The advantage is eliminating as many connectors and as much small gauge wiring as possible. Elimination of connectors and small wire reduces the resistance in the circuit and ultimately, the voltage drop. This has always resulted in brighter headlights on these vehicles. Lots of good information and a more technical description at MadElectrical.com - Mad Enterprises
Headlight relay article here:
Catalog
Good Luck!
Mark another vote for "relays!" I've used them on several vehicles, with and without headlight upgrades. The advantage is eliminating as many connectors and as much small gauge wiring as possible. Elimination of connectors and small wire reduces the resistance in the circuit and ultimately, the voltage drop. This has always resulted in brighter headlights on these vehicles. Lots of good information and a more technical description at MadElectrical.com - Mad Enterprises
Headlight relay article here:
Catalog
Good Luck!
Thread Starter
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Hotshot
Joined: Nov 2000
Posts: 11,591
Likes: 14
From: Pflugerville, tx
But then you run the power to the lights down the long runs to the bulbs..?
Did you increase the wire size too?
I was thinking of moving the relays under the front gravel gaurd, short haul for the +12V to the bulbs. Battery is in the engine compartment for me.
the main harness wires will be coming thru the chassis at the gravel guard
(no wires showing in the engine compartment other than the two battery leads and this one hot wire to the relays..)
I need one feed for the dual fans, and one feed for the lights. figured I could hang them on the gravel guard cross support (bottom to top of gravel guard)..
sam
Did you increase the wire size too?
I was thinking of moving the relays under the front gravel gaurd, short haul for the +12V to the bulbs. Battery is in the engine compartment for me.
the main harness wires will be coming thru the chassis at the gravel guard
(no wires showing in the engine compartment other than the two battery leads and this one hot wire to the relays..)
I need one feed for the dual fans, and one feed for the lights. figured I could hang them on the gravel guard cross support (bottom to top of gravel guard)..
sam
Laughing Gas
Joined: Feb 2002
Posts: 932
Likes: 9
From: DFW, TX
Sam,
The last time I did this, I ran the wire from the battery instead of the alternator. It was still an improvement, but picking up power at the alternator "sensing" point provides the most improvement.
The wire from the battery was 10 awg with a 30 amp self resetting circuit breaker near the battery. This provided the power to both the "high beam" and "low beam" relays. The existing wire harness was used to turn the relays "on" and "off." A 12 awg wire was run from each relay to each headlight. The relays I purchased had two "output" terminals so each headlight had it's own connection with no splices required. I think I picked these up at Auto Zone for ~$8 each.
Hiding the relays behind the grill works well. I'm not sure where you are talking about "under the gravel guard." I would protect the relays from dirt and crud from under the truck, if possible. You might also want to get "relay bases" that allow the relay to be snapped into the base. These are a little harder to find, but if the auto parts store doesn't have them, check with your local car stereo installer. They used them frequently to power amps and such.
Good Luck!
The last time I did this, I ran the wire from the battery instead of the alternator. It was still an improvement, but picking up power at the alternator "sensing" point provides the most improvement.
The wire from the battery was 10 awg with a 30 amp self resetting circuit breaker near the battery. This provided the power to both the "high beam" and "low beam" relays. The existing wire harness was used to turn the relays "on" and "off." A 12 awg wire was run from each relay to each headlight. The relays I purchased had two "output" terminals so each headlight had it's own connection with no splices required. I think I picked these up at Auto Zone for ~$8 each.
Hiding the relays behind the grill works well. I'm not sure where you are talking about "under the gravel guard." I would protect the relays from dirt and crud from under the truck, if possible. You might also want to get "relay bases" that allow the relay to be snapped into the base. These are a little harder to find, but if the auto parts store doesn't have them, check with your local car stereo installer. They used them frequently to power amps and such.
Good Luck!
Elder User
Joined: May 2006
Posts: 907
Likes: 1
From: Kansas City, Mo
Unless you want them exposed to water I would mount them as many car manufactures do, on the firewill, in the engine bay. Buy all three relays the same so you can switch them to troubeshoot problems. The idea is to keep high amp use items away from your switches/fuse panel/under dash area and provide direct batt to component through relay connected wiring.Fires and fuse box melt downs have been around a long time. Unless you are using a old or under size battery, a couple feet of wire is not going to make that much of a differance, remember the relay for the elect fuel pump in the tank has several feet of wire and it works ok. The average three relays: elect fan, fuel pump and headlights. Some may put high amp music systems, etc. All high amp relays contacts arc and slowly wear out so don't buy Chinese made. Relays should have amp rating written on them. Have a great day,chuck
Thread Starter
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Hotshot
Joined: Nov 2000
Posts: 11,591
Likes: 14
From: Pflugerville, tx
thanks.. I do NOT want them located in the engine bay.. no wire runs visible.
the engine wiring itself will be inside a chrome pipe with cutouts for the leads to individual components (with leads as short as reasonable for each).
Sam
the engine wiring itself will be inside a chrome pipe with cutouts for the leads to individual components (with leads as short as reasonable for each).
Sam
Elder User
Joined: May 2006
Posts: 907
Likes: 1
From: Kansas City, Mo
Sam, I lived in Houston for almost 20 years. My son had a HO mustang in the eightys having a alternator down low in the steering pump area. When it rained, the under passes flooded and shorted out the alt ($350.00). The relays we are talking about have one side direct to the battery. If it shorts out, the truck dies and flooding/loss begins. I understand the clean look. I just wanted you to be aware of potential problems. Have a great day,Chuck