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Old 03-06-2005, 01:42 AM
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Help Wiring A Relay to A Dash Switch

Help me out here -- my head feels like a bowl of spaghetti and I can't figure out how to wire a switch for my backup lights to a relay.

The Switch has 2 terminals ... one for a ground and one for positive power. Simple enough.

The Relay has 4 terminals:
#30 = Power ... gets connected to my power line from the fuse box - right?
#86 = magnetic coil winding/Positive ... goes to the switch??? Which terminal; positive?
#85 = magnetic coil winding/Negative ... goes to ground. That I know.
#87 = output ... goes to my backup lights. That I also know.

I guess I'm confused about #30 and #86 on the relay AND how to wire the switch.

So ... does #30 go to the fuse box/power and #86 to the positive terminal on the switch ... and the negative terminal on the switch goes to ground?

Or does #30 get power from the switch; in which case, how do I wire the switch? See? I'm all twisted up on this for some reason.

Also -- A relay is rated at 20 amps ... since my switch is also rated at 20 amps, does it make sense to use a relay at all?

Thanks.

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Old 03-06-2005, 08:24 AM
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the back up lights do not draw enough current to justify a relay, it is really not needed just for 2 lil ole lights. good luck with your project.
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Old 03-06-2005, 08:37 AM
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hope this helps ya alan....joe

relay wiring <~~ 1 lite
relay wiring #2 <~~ 2 lites
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Old 03-06-2005, 09:52 AM
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Ole Bull -- Thanks, bro'. Note: These ol' trucks didn't come with backup lights, so I put parking lights from a 49 Chevy pickup in the back -- they are double filament bulbs and I hooked up both filaments, from each bulb, to positive to make 'em nice and bright. Do you STILL agree that I don't need a relay? The relay is rated at 20 amps and my switch is also rated at 20 amps ... so I WAS questioning whether or not the relay would matter.

Hey, Joe -- Thanks, buddy! I have a schematic from MadElectrical that does a different wiring pattern than yours ... it looks like yours is using the ground from the switch to turn on the relay, while MadElectrical is, instead, using the positive from the switch to turn it on. I guess you can do it either way, huh?

Here's MadElectrical's diagram:



I think I'm just gonna forget the relay and do this the "easy" way.

Alan
54 Chevy Pickup
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Old 03-06-2005, 10:54 AM
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Your circuit is correct. Terminals 86 & 85 are interchangeable and terminals 30 & 87 are interchangeable too.
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Old 03-06-2005, 01:00 PM
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Thanks, Willys36 ... check this out; I've been doing some "homework:"

Here's the inner workings of the relay:

1 - When the dash switch is OFF we get the Spring-Pull and #87 is OFF ... #87a is ON (if used).

2 - When the dash switch is ON we get the Magnetic-Pull and #87 is ON ... #87a is OFF (if used).



We can turn things on with a Positive feed from our switch:



Or we can turn things on with a Ground feed from our switch:



Did I do my homework correctly ... or what?


Alan
54 Chevy Pickup
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Old 03-06-2005, 02:58 PM
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Yes. Your original relay was a 'single pole - single throw' (SPST) style so it doesn't matter whether you heat up 87 or 30. Hoewever the second diagram is of a 'single pole - double throw' (SPDT) style so you ndeed to take care to heat up pole 30 so it can switch between 87 & 87A. The other two terminals are activated by your switch and turn on the electromagnet that moves the switching contacts so it doesn't matter to it how it gets charged, the magnet will work regardless. Thre two switching diagrams you show will both work fine.
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