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Relay or Diode?

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rpaxton

Joined: Sep 07 2009
Posts: 5


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Post Tue Mar 09, 2010 6:18 am

Here is my project:

I am wiring a set of courtesy lights to a boat trailer. I want these lights to come on when the truck is in reverse and also be able to activate them with a manual switch in the cab.

My concern with this setup is that most automatic transmissions are shifted electricaly now, and I don't want to back feed the circuit and shift the tranny into reverse when I am not behind the wheel.

My questions is would it be easier / better to use relays wiring this circuit or diodes? Can anyone suggest a wiring diagram for this circuit?

Thanks in advance!

Rodger
Phil
Owner, Oznium.com

Joined: Feb 11 2003
Posts: 7719


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Post Tue Mar 09, 2010 6:55 am

A diode would likely work (you'd have to make sure you get a large enough one to handle the current).

Or here's a nice diagram for you which shows how to do it with a relay.

User posted image

I'm assuming the stock reverse light circuit it positive switched (with a constantly connected ground wire).
EricCartman

Joined: Oct 24 2008
Posts: 175
Location: Oregon


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Post Tue Mar 09, 2010 9:21 am

I used both. icon_smile.gif

User posted image

The master switch allows you to prevent the reverse lights from coming on at all. Sometimes you don't want them too. And I was too lazy to mess with building a light sensor to do it only when it was dark... but maybe when I get bored. :p

The aux light allows you to turn the lights on without being in reverse (really nice for the diptards that like to tailgate you at night, or keep their bright lights on).

The diode on the relay is probably overkill, but diodes are cheap. icon_smile.gif

I used 1N4001 didoes, in case you are wondering.

Good luck,
Cartman
rpaxton

Joined: Sep 07 2009
Posts: 5


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Post Wed Mar 10, 2010 2:06 am

One last question:

On the relays I am assuming that they are single pole single throw (SPST)?

Thanks again for the help guys!!

Rodger
Phil
Owner, Oznium.com

Joined: Feb 11 2003
Posts: 7719


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Post Wed Mar 10, 2010 2:11 am

Btw, Oznium offers a relay that'd work: https://www.oznium.com/wire-12v-and-relays/relay40

SPST or SPDT would both work
clutch1

Joined: Oct 08 2006
Posts: 1928
Location: around hurr.


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Post Wed Mar 10, 2010 10:37 am

rpaxton wrote:


My concern with this setup is that most automatic transmissions are shifted electricaly now, and I don't want to back feed the circuit and shift the tranny into reverse when I am not behind the wheel.



You don't need to worry about this part! Reverse, park, and drive are all achieved through the use of a manual valve connected directly to your shifter. That way if you have total electrical failure you can still drive the car, but you'll be stuck in one forward gear.
The electrical shifting is done through the use of two solenoids that bleed pressure from a valve when they're open. Depending on which solenoid are open, the valve moves to a different spot in its bore, turning on different hydraulic circuits in the trans, engaging different clutch packs, putting it in different gears!

biglaugh.gif
rpaxton

Joined: Sep 07 2009
Posts: 5


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Post Fri Mar 12, 2010 3:12 pm

Clutch1,

I totaly agree with your description of how a transmission works. My concern is 1. it is a Ford (truck) we all know what that stands for icon_rolleyes.gif

and 2. I have had installers of police equipment tell me that they won't install the "Park siren disable switch" because Fords are notorious for "slipping" out of gear, and that Ford states this is the "main culprit" for Ford police interceptors slipping out of park. Maybe (read that as probably) it is Ford just trying to cast blame, but either way I don't want to take the chance of back feeding that circuit.

I will probably put a relay on the OEM back up light wiring, and put a diode on the after market wiring just to be safe. I don't want to call my insurance agents and try to explain how truck, trailer, and boat ended up in the drink. icon_eek.gif

Thanks for all the replys! icon_lol.gif

Rodg
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