another head lite question
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Senior User
Joined: Nov 2010
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From: Chesapeake Va.
another head lite question
Just got for "FREE" a set of after-market head lites and want opinions,
They are made by DONG JIN industries BRITE WHITE H4 12volt 100/80w
Would they be safe to run without the wiring upgrade?
They are made by DONG JIN industries BRITE WHITE H4 12volt 100/80w
Would they be safe to run without the wiring upgrade?
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 83
From: NorCal
A relay is simply a high current electro-magnetic switch. It is activated by a separate signal to energize (and de-energize) a separate high current circuit.
Let's use a fog light circuit for example. Instead of the light being turned on by a switch in the cab through which all the current flows through to illuminate it, the in-cab switch sends a low amp signal to the relay which gets energized (you'll hear a click). The relay, in turn, supplies the current to turn on the light.
What is being suggested is to use the headlight signal (the stock pull-on switch in the cab) to turn on a relay connected between the battery and the new headlights.
The advantage with relays is that they can supply and withstand a high current load via thicker gauge wiring with very low voltage loss than if the current has to go from the battery, to a switch in the cab, and finally to the headlights. Instead of 15 feet of wiring, you'll likely end up with about half that.
Using the formula (P/E)=I... P is Watts, E is Volts and I is Amperes....
.... you get 100 watts/12 VDC =8.33 amps per light. Therefore, use a relay with at least a 20-amp rating.
Let's use a fog light circuit for example. Instead of the light being turned on by a switch in the cab through which all the current flows through to illuminate it, the in-cab switch sends a low amp signal to the relay which gets energized (you'll hear a click). The relay, in turn, supplies the current to turn on the light.
What is being suggested is to use the headlight signal (the stock pull-on switch in the cab) to turn on a relay connected between the battery and the new headlights.
The advantage with relays is that they can supply and withstand a high current load via thicker gauge wiring with very low voltage loss than if the current has to go from the battery, to a switch in the cab, and finally to the headlights. Instead of 15 feet of wiring, you'll likely end up with about half that.
Using the formula (P/E)=I... P is Watts, E is Volts and I is Amperes....
.... you get 100 watts/12 VDC =8.33 amps per light. Therefore, use a relay with at least a 20-amp rating.
Last edited by HIO Silver; Jan 16, 2011 at 09:47 PM. Reason: Bad syntax!
Thread Starter
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Senior User
Joined: Nov 2010
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From: Chesapeake Va.
Yea I'm familiar with the relay part but it was the wording by orfordguy that threw me off "high volt".
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Junior User
Joined: Jan 2011
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not really hi voltage voltage, just let's the power go through the relay instead of the headlight switch and draw to many amps.
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Post Fiend
Joined: Jul 2004
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From: Northern California
The stock Headlamp wiring isn't designed or rated for the amperage increase above stock Headlamps.
The Factory headlamps on all Ford Pickups before 1981 are regular "non-halogen" incandecent headlamps.
Even upgrading to regular halogen headlamps can put too much amperage on the headlamp circut and cause "flickering light syndrome", where the headlamp switches circut breaker (rated for 15 amps) triggers on and off in succession.
I highly recommend putting in a relay system if using headlamps other than factory type.
The Factory headlamps on all Ford Pickups before 1981 are regular "non-halogen" incandecent headlamps.
Even upgrading to regular halogen headlamps can put too much amperage on the headlamp circut and cause "flickering light syndrome", where the headlamp switches circut breaker (rated for 15 amps) triggers on and off in succession.
I highly recommend putting in a relay system if using headlamps other than factory type.
Senior User
Joined: Jul 2009
Posts: 180
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From: Up North
The Heavy Duty Light Harness Has relays and fully pakaged for $30. Iv'e used this on my 79 F250 and 78 Bronco, Takes about 30 minutes to install and the light output with Silverstar bulbs is impressive to say the least.
All the power to the lights will run from the battery giving you a couple of extra volts to the lights and not overloading the headlight wiring.
LMC Truck Parts - Page 149
All the power to the lights will run from the battery giving you a couple of extra volts to the lights and not overloading the headlight wiring.
LMC Truck Parts - Page 149
Elder User
Joined: Feb 2009
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From: Sweethome Or
now you guys get it.. i ment high volt becuase there are some cheap low volttage relays and these will burn up causing a potential fire.. the wiring relay setup previously mentioned is perfect...
Tuned
Joined: Mar 2005
Posts: 479
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From: Mesa AZ
automotive relays are rated at 12 volts +- a few. you mean "low amperage rating" its not voltage that burns the wiring up, its too high of current. a good 30amp rated relay will be plenty.
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