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Author Topic: Headlight relay schymatic  (Read 2061 times)

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Offline Mad Max

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Headlight relay schymatic
« on: June 12, 2010, 01:42:38 PM »
Peeps, I just did up a schymatic for wiring in relays for the headlights on a 70's (particularly a '77) Dodge Truck.  I did this for myself as I'm doing the wiring for Paddy's Wagon now, and I wanted to make sure I got it right.  

The Bottom Line is my attempt at a very short and consice explaination for how the relays 'work' and how they're wired into the harness.

The color chart pertains to the relays we got from Del City and the explaination is aimed at a Dodge truck.  I think they're the 'same' as other typical relays available.

Please have a gander and let me know if I'm gonna burn down the truck :P ;D




Many thanks
- Sam
« Last Edit: June 12, 2010, 01:46:26 PM by Mad Max »
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Offline ToxicDoc

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Re: Headlight relay schymatic
« Reply #1 on: June 12, 2010, 04:33:06 PM »
The 30 amp fuses are too high unless you have more of a draw on the circuit.  A standard 65 watt high beam will draw 6.5 amps at 12 volts (65 watts/voltage).  You could use a 20 amp fuse and gain a larger margin of safety.
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Offline s ǝoɾ

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Re: Headlight relay schymatic
« Reply #2 on: June 12, 2010, 05:16:34 PM »
The 30 amp fuses are too high unless you have more of a draw on the circuit.  A standard 65 watt high beam will draw 6.5 amps at 12 volts (65 watts/voltage).  You could use a 20 amp fuse and gain a larger margin of safety.
65/12=5.41 'Doc  ;) BUT you have 2 beams. 20amps is still sufficient either way just wanted to point out math.  Circuit breakers may be even better. {cool}

You can do a 3rd relay trick so when high beams are selected it will turn on both filaments for "super" high highbeams.

Of course this is best performed with the upgraded composite housing and ceramic "heavy duty" blue/yellow connectors for added "beef".

Let's talk about feed wires?
Avoid replacing any part that you have not proven to be faulty through extensive testing.

Offline ToxicDoc

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Re: Headlight relay schymatic
« Reply #3 on: June 12, 2010, 05:33:02 PM »
65/12=5.41 'Doc  ;) BUT you have 2 beams. 20amps is still sufficient either way just wanted to point out math.  Circuit breakers may be even better. {cool}

You can do a 3rd relay trick so when high beams are selected it will turn on both filaments for "super" high highbeams.

Of course this is best performed with the upgraded composite housing and ceramic "heavy duty" blue/yellow connectors for added "beef".

Let's talk about feed wires?

I knew that, somehow I put 10 volts in my head and got 6.5 out...
'85 W150 SB, 408 stroker, Magnum manifolds, Performer RPM, 670 Truck Avenger, HEI ignition, Auburn LSD 9.25 and '82 D44 (non-CAD) with 3.55/3.54,  NV4500/NP241

Offline EdmCharger1

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Re: Headlight relay schymatic
« Reply #4 on: June 12, 2010, 06:25:44 PM »
I think it is awesome that you are helping people by posting these wiring diagrams, but I am curious why you use numbers instead of just showing the coil and the NO and NC contacts like a schematic should be? I noticed a most people on here use those numbers, but if you are using a different relay, those numbers won't be the same.

Offline ToxicDoc

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Re: Headlight relay schymatic
« Reply #5 on: June 12, 2010, 06:37:41 PM »
I think it is awesome that you are helping people by posting these wiring diagrams, but I am curious why you use numbers instead of just showing the coil and the NO and NC contacts like a schematic should be? I noticed a most people on here use those numbers, but if you are using a different relay, those numbers won't be the same.

Those numbers are industry standard and used worldwide.
'85 W150 SB, 408 stroker, Magnum manifolds, Performer RPM, 670 Truck Avenger, HEI ignition, Auburn LSD 9.25 and '82 D44 (non-CAD) with 3.55/3.54,  NV4500/NP241

Offline s ǝoɾ

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Re: Headlight relay schymatic
« Reply #6 on: June 12, 2010, 06:51:16 PM »
I think it is awesome that you are helping people by posting these wiring diagrams, but I am curious why you use numbers instead of just showing the coil and the NO and NC contacts like a schematic should be? I noticed a most people on here use those numbers, but if you are using a different relay, those numbers won't be the same.

It's a bosch/tyco/ISO standardized number system for automotive use.

These are regularly available off the shelf, even at walmart. If you do not need pin #87a, you can upgrade to the 70amp 4 pin "horn" relay. Longer life due to stronger contacts, but no normally closed function.


A blocking diode will also work between the high and low beam trigger wires if you prefer a solid state alternative.

This allows high beam trigger to bleed into and turn on low beam trigger as well, but not vice versa. A one way valve.
« Last Edit: June 12, 2010, 06:55:12 PM by s ǝoɾ »
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Offline Mad Max

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Re: Headlight relay schymatic
« Reply #7 on: June 12, 2010, 08:06:25 PM »
okay so I got the basics correct, ja?  I had always wondered about the 'feed wire' per component, and that was part of my issue is determining the best way to get at a feed wire, and is sounds like using the actual factory wire used to originally go to the component, ja?

I think it is awesome that you are helping people by posting these wiring diagrams, but I am curious why you use numbers instead of just showing the coil and the NO and NC contacts like a schematic should be? I noticed a most people on here use those numbers, but if you are using a different relay, those numbers won't be the same.

The main reason is the way I wrote it is just how I 'understand' it - I know there is a lot more technical version but this is the one I can 'comprehend'.  I figure there's lots of other folks in here that unlike Joe are not electrical gurus that the basic 'generic explaination might make more sense :).  Ya havta understand, wiring/electrical is my absolute #1 nemesis - making a correct schymatic that I can understand is a BIG leap forward for me  ;D

- Sam
Official:  RamJam 2014 - Moab, Utah!!   8-12 September (Monday-Friday) - http://ramchargercentral.com/ram-jam/ramjam-2014-moab-utah-8-12-september-(official-dates)/


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Offline s ǝoɾ

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Re: Headlight relay schymatic
« Reply #8 on: June 12, 2010, 08:20:12 PM »
I think an aux fuseblock makes a good junction point for your feedwires, although I might still consider circuit breakers instead.

I'm trying to find a source of those ceramic connectors, I know I have seen them, just don't remember where.
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Offline KThaxton

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Re: Headlight relay schymatic
« Reply #9 on: June 12, 2010, 08:46:35 PM »
I realize I sound like a broken record, but I'd use fusible links instead of fuses, or breakers like Joe suggested.....anything but fuses.  ;)
STOP PLATE TECTONICS!

You're absolutely correct, Kendall. My mistake  ;D

Offline s ǝoɾ

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Re: Headlight relay schymatic
« Reply #10 on: June 12, 2010, 09:02:08 PM »
I realize I sound like a broken record, but I'd use fusible links instead of fuses, or breakers like Joe suggested.....anything but fuses.  ;)

Interesting point. Since the inrush current on cold headlights is many times greater than the "operational draw" you may have a hard time keeping fast blow fuses from doing what they do...blowing.
 I mean a headlight may draw many times over the normal current until the filament heats up and resistance increases.

Where as a fusible link (cartridge or wire) or breaker should be able to handle those short surges while still being small enough to protect the wires.
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Offline Killerbee

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Re: Headlight relay schymatic
« Reply #11 on: June 12, 2010, 09:04:07 PM »
FWIW, the original headlamp switches, like the one in the dash, usually use a breaker.  They were called "thermal fuses", and would open if the switch got too hot.  Then after cooling down a while they'd close.

If you use a fusible link, label it well...  I'd recommend a quality fuse or a quality breaker.  It'd suck pretty bad to be someplace at night and have the headlights go out...  But it should only be the hi OR low beams, not both   :)

I'll also put in a plug for the RCC relay FAQ, as short as it may be...
http://www.ramchargercentral.com/electrical/relay-faq/

Ben

Offline SuperBurban

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Re: Headlight relay schymatic
« Reply #12 on: June 12, 2010, 09:26:09 PM »
Not to be the one to be quoting DOT regs all the time here, but DOT rules call for Circuit breakers for headlights, and since Sam is talking about pulling big trailers, he does have the chance of being pulled in to a DOT check point, that is clearly the way to go.
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Offline KThaxton

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Re: Headlight relay schymatic
« Reply #13 on: June 12, 2010, 10:52:46 PM »
Interesting point. Since the inrush current on cold headlights is many times greater than the "operational draw" you may have a hard time keeping fast blow fuses from doing what they do...blowing.
 I mean a headlight may draw many times over the normal current until the filament heats up and resistance increases.

Where as a fusible link (cartridge or wire) or breaker should be able to handle those short surges while still being small enough to protect the wires.

Additionally (broken record again) lots of current+long periods of time+poor connections (blade fuses)=burnt fuse holder.

The picture below was the main feed to an airbag compressor on my brother-in-laws '08 F350 that was hacked in by some previous owner idiot. Just jam some foil in there, that'll make it better.  ::)

I'd recommend a quality fuse or a quality breaker. 

Quality of fuse doesn't matter, it's the connection that matters.

Not to be the one to be quoting DOT regs all the time here, but DOT rules call for Circuit breakers for headlights, and since Sam is talking about pulling big trailers, he does have the chance of being pulled in to a DOT check point, that is clearly the way to go.

Strange, I've never heard that. Do you have a link? I'm curious.
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You're absolutely correct, Kendall. My mistake  ;D

Offline Mad Max

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Re: Headlight relay schymatic
« Reply #14 on: June 12, 2010, 11:33:03 PM »
my bad - i had my terms mixed.  When I said 'feed' wire I was thinking 'trigger' wire (from the factory engine bay harness and ultimately the headlight switch, which is via the foot dimmer...).  Copy all on the actual main battery feed wire and the connections.

Good point on the DOT rules George.  I can certainly apply those tips when time comes.  For Pat's truck the fuseable links should work quite well.

Kendall, your pic of the fuse holder is exactly what Nacho's power feed for the dual rad fans looked like after not very long, and it crapped out right in the middle of Hells Revenge - lovely.

Great discussion fellas, thanks.
Official:  RamJam 2014 - Moab, Utah!!   8-12 September (Monday-Friday) - http://ramchargercentral.com/ram-jam/ramjam-2014-moab-utah-8-12-september-(official-dates)/


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Offline KThaxton

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Re: Headlight relay schymatic
« Reply #15 on: June 12, 2010, 11:43:40 PM »
Kendall, your pic of the fuse holder is exactly what Nacho's power feed for the dual rad fans looked like after not very long, and it crapped out right in the middle of Hells Revenge - lovely.


Did you get a picture? We need more proof for these people that don't believe us when we tell them to use fusible links instead of fuses for high current drawing circuits. Cooling fans are the perfect example.

Years ago I tried to tell Klaus (santak) not to use fuses for his fans. Not long after, I had the pleasure of giving him an "I told ya so".  ;D
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You're absolutely correct, Kendall. My mistake  ;D

Offline s ǝoɾ

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Re: Headlight relay schymatic
« Reply #16 on: June 12, 2010, 11:52:23 PM »
We know what fuses look like, and we thought we knew what fusible links look like.

Here are some other options:

Fusible Link (replaceable)


ATO type breaker


Auto resetting breaker


Avoid replacing any part that you have not proven to be faulty through extensive testing.

Offline SuperBurban

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Re: Headlight relay schymatic
« Reply #17 on: June 13, 2010, 08:50:43 AM »

Strange, I've never heard that. Do you have a link? I'm curious.

I'll find the other one for you later, here is the main one they still use to hang drivers on when they want to .


§393.95 Emergency equipment on all power units.

Each truck, truck tractor, and bus (except those towed in driveaway-towaway operations) must be equipped as follows:
 
(a) Fire Extinguishers
(b) Spare fuses. Power units for which fuses are needed to operate any required parts and accessories must have at least one spare fuse for each type/size of fuse needed for those parts and accessories.


Apparently they dropped it from the newer version, but it read something like: trucks built before 1968 had to be retrofitted with circuit breaker headlight systems, by 1982.
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Re: Headlight relay schymatic
« Reply #18 on: June 13, 2010, 10:54:30 AM »
Ahh, so this is specific to heavy trucks, i.e. not passenger cars and light trucks?
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Offline SuperBurban

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Re: Headlight relay schymatic
« Reply #19 on: June 13, 2010, 10:56:35 AM »
Ahh, so this is specific to heavy trucks, i.e. not passenger cars and light trucks?
Sam has been talking about pulling a trailer over 10,000 lbs, that classifies as a heavy truck.  ;)
"The fact that we are here today to debate raising America’s debt limit is a sign of leadership failure."

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Offline moparmike72

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Re: Headlight relay schymatic
« Reply #20 on: June 13, 2010, 11:49:38 AM »
my bad - i had my terms mixed.  When I said 'feed' wire I was thinking 'trigger' wire (from the factory engine bay harness and ultimately the headlight switch, which is via the foot dimmer...).  Copy all on the actual main battery feed wire and the connections.

The easy way to hook up the trigger wires would be to plug into the existing driver's side headlight connector with a pair of blade connectors and run the wires to a pair of relays mounted next to the battery. Put your circuit breaker(or fuse) between the battery and the relays. Run wires, with new seal beam connectors attached, out to the headlights and you're done. Anytime you want to revert back to the original setup all you need to do is reach behind the headlights and swap the new seal beam connectors for the old ones. Mount the components on a breadboard, mounted next to the battery, and you can remove the whole thing as a unit when you sell the truck or decide to use it on another one.
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Offline moparmike72

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Re: Headlight relay schymatic
« Reply #21 on: June 13, 2010, 01:46:55 PM »
This guy markets relay kits and electrical stuff for bikes:
www.easternbeaver.com
He has some nice 20 amp sealed 4 pole relays and oem style connectors to wire them up, some nice waterproof fuse holders also.
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Offline s ǝoɾ

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Re: Headlight relay schymatic
« Reply #22 on: June 16, 2010, 03:24:05 PM »
Hmm, I think I may have found a 2 relay solution for super high beams.

With a little wiring modification, you can provide hot side power to BOTH relays at pin #86. Directly off the dash switch, completely bypassing the dimmer.

Ground pin 85 of low beam relay to chassis.

Quote
But if you give both relays hot, won't both lights be on all the time?

No, since the high beam relay is not grounded, it will do nothing.

Then ground dimmer switch or any other water resistant switch directly to floor board. The output wire from that switch is your ground for high beam relay.

Step on it, both beams are on in full effect. Step on it again, low beams only.

Also have less hot wires running through firewall. If the dimmer switch/wire shorts, there isn't a fire risk, you will just have super bright lights any time the switch is on. Better fail safe than the fiery alternative. If the dimmer switch/wire opens, you just lose highbeams only.
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Offline Bogie

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Re: Headlight relay schymatic
« Reply #23 on: June 18, 2010, 03:30:10 AM »
Nice work Sam I never drew out a diagram but I'm running 4 relays as I needed to separate the high beams side to side for the emergency flashers. As far as running both filaments what i did was connect the input to the dimmer switch to the low beam out put so they come on all the time when the dash switch is on the dimmer switch then only controls the high beams on/off.
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