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Electrical... Talk & Q&A! Electrical Q&A.. The shocking truth, tips, tricks & more!

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  #1  
Old 07-01-2010, 10:38 PM
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LarryH LarryH is offline
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Default Headlight relay.

I need to install a headlight relay in my T-Bucket (the original builder didn't install one). The only thing i know about electricity is if i touch the wrong thing it can really hurt and if it ain't done right it can make a really pretty fire.

Do i need two relays (one for low beam, one for high beam)? Should it be wired in before or after the light switch? Does anyone have a simple wiring diagram?
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Old 07-02-2010, 06:48 AM
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Does this help?!

http://www.opiebennett.com/tech/headlight/diagram.jpg

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Old 07-03-2010, 09:07 AM
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I followed this article. Bob's diagram looked like it was using some kind of pre-made wiring harness.

http://www.ford-trucks.com/article/i...r_Brights.html

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Old 07-04-2010, 11:07 AM
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To answer your question whether or not you need a relay for both the high and low beams, yes, one for each. In fact, you need one for other high draw items like electric fan, electric fuel pump, heater blower motor, etc. The purpose of a relay is to allow you to supply high current to the accessory while only using a small amount of current through the switch. If you run all that current through the switch it can burn them out and cause short circuits. You will also get other problems like dim lights and slow running fans.

If your previous owner didn't use relays it makes you wonder where he cut other corners on the wiring. You may want to consider just buying a good wiring kit and redoing the whole thing. The kits make it so much easier if you follow them step by step and nothing is worse (or more dangerous) than a shoddy wiring job. Lots of cars have burned up because of some short circuit or other wiring issue. You not only want relays but lots of fuses or circuit breakers.

Even on a simple system like on my T you can see how many relays and fuses I ran.

Don

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Old 07-04-2010, 07:47 PM
bob w bob w is offline
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I do not disagree with Don or anyone else regarding relays. However, I don't use them at all. I use all 50 amp capacity switches and use wire at least one gauge heavier than the load requires and use the correct rating fuse. I solder all connections and cover them with shrink tube. Never have burned out a switch or had a short in over 50 years of hot rod building. Just letting you know it can be done without relays.
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Old 07-04-2010, 11:14 PM
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Sure, that would work. The weak link is normally the switches, the garden variety just aren't made to handle high loads. Those 50 ampers you mention are designed to do that. More than one way to skin a cat.

Don
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Old 07-05-2010, 03:45 PM
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Ill throw another diagram into the pot.LOL
Attached Images
File Type: jpg GMC Headlite Relay Diagram 1.jpg (31.0 KB, 65 views)
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  #8  
Old 07-31-2010, 10:22 PM
rdixiemiller rdixiemiller is offline
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Default Relays Vs. Switches

All things being equal, I would use heavy switches and wiring and not use relays. just more things to go wrong IMHO. However, if I had some really cool vintage switches I wanted to use, then I would use the switches to operate a relay.
All depends on what you want o spend your money on. Relays are not really expensive.
Oh yeah, ALWAYS use a fuse or a circuit breaker. You will not believe how much fun it is NOT to have smoke start boiling from under the dash while you are tooling down the street! Burns the snot out of your hands as you try to snatch the burning wires loose before the car goes up!
Ask me how I found that out!
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Old 11-01-2011, 07:04 AM
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Sams diagram shows the COMPLETE system,
including the CONTROL circuitry, the other two don't show the "whole thing".

(Control Circuitry includes the Dimmer Switch and Relay Control Switches)
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  #10  
Old 11-01-2011, 11:10 AM
railroad railroad is offline
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Quote:
Originally Posted by rdixiemiller View Post
All things being equal, I would use heavy switches and wiring and not use relays. just more things to go wrong IMHO. However, if I had some really cool vintage switches I wanted to use, then I would use the switches to operate a relay.
All depends on what you want o spend your money on. Relays are not really expensive.
Oh yeah, ALWAYS use a fuse or a circuit breaker. You will not believe how much fun it is NOT to have smoke start boiling from under the dash while you are tooling down the street! Burns the snot out of your hands as you try to snatch the burning wires loose before the car goes up!
Ask me how I found that out!
I had a radar detector smoke the wire on me. Definitely a wake up. When I bought my T Bucket, used, one of the best additions was a battery disconnect switch. Anytime I have to do some electrical work, I have the luxury of just turning a switch. One other item, I just added Speedways headlight switch that has the hi and low beam functions included in the switch. It is also heavy duty, no relay needed.

Last edited by railroad; 11-01-2011 at 05:09 PM.
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