Getting power from the starter relay?
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Postmaster
Joined: Jun 2001
Posts: 2,809
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From: Loveland, CO.
Getting power from the starter relay?
I have been trying to ask this question, but I'm not sure that I have been phrasing it correctly. I need a power supply inside of my truck that only works when the key is on, to power the ac/heater and turn signal/od/rear defrost/backup light fuses. The wire to them is bad somewhere up in the dash. Can I get a power lead like this from the starter relay (I think that it is the starter relay, it's the round black box on the passenger side fender under the hood, and a wire goes to the starter, among other wires). I would think that the hot side would only be hot when the key is turned. If this is true, then is it ok to take power off of it to feed the fuses in question? Or does it only have power when the key is turned all the way to engage the starter? If I can't use the relay, where should I get a switched power supply?
Senior User
Joined: Oct 2002
Posts: 157
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From: Vermont, USA
Getting power from the starter relay?
[updated:LAST EDITED ON 03-Jan-03 AT 02:15 PM (EST)]>Or does it only have power when the key is turned all the way to
>engage the starter? If I can't use the relay, where should I get a
>switched power supply?
It will only be hot when the key is turned all the way. Once you stop cranking the starter the line will go dead. This is not what you want.
I'm not sure where there would be a source. How taping off the power going to the radio? That should be easy to access.
>engage the starter? If I can't use the relay, where should I get a
>switched power supply?
It will only be hot when the key is turned all the way. Once you stop cranking the starter the line will go dead. This is not what you want.
I'm not sure where there would be a source. How taping off the power going to the radio? That should be easy to access.
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Postmaster
Joined: Jun 2001
Posts: 2,809
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From: Loveland, CO.
Getting power from the starter relay?
I need a supply that can support an additional 45 amps, I have something working now but I want to be sure that it won't get overloaded. In other words, I want to go to the "source" of the switched power, but I don't know where that is (ie. the "source" of unswitched power could be the battery).
New User
Joined: Dec 2002
Posts: 22
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From: Simpsonville USA
Getting power from the starter relay?
You could put a relay on the power to the radio so that when the power is on it switches your relay on giving you a switched power supply.
I'm not sure about the total amps one can handle but relays used for fog lights are rated at 30 amps. I'm sure there are stronger ones out there.
I'm not sure about the total amps one can handle but relays used for fog lights are rated at 30 amps. I'm sure there are stronger ones out there.
Post Fiend
Joined: Nov 2002
Posts: 9,987
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From: Memphis, TN
Getting power from the starter relay?
The "source" of switched power is the ignition switch 
:P, but you can't pull 45A thru it. You'll have to tap a switched circuit (like the radio or EEC) and add a relay or 2. If you can separate the 45A load into smaller ones (like ~25A or less each), you won't have any problem using several relays if you use a separate relay for each circuit.
But if the load is all on one circuit (like a BIIIG light bulb, heating element,or motor), then you'll need a more sophisticated circuit (including an inductor) to prevent multiple relays from burning out frequently. In other words, if it's a single 45A load, you're better off finding a 50A relay for it.
:P, but you can't pull 45A thru it. You'll have to tap a switched circuit (like the radio or EEC) and add a relay or 2. If you can separate the 45A load into smaller ones (like ~25A or less each), you won't have any problem using several relays if you use a separate relay for each circuit.But if the load is all on one circuit (like a BIIIG light bulb, heating element,or motor), then you'll need a more sophisticated circuit (including an inductor) to prevent multiple relays from burning out frequently. In other words, if it's a single 45A load, you're better off finding a 50A relay for it.
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