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Discussion Starter · #1 ·
How much power can you pull off the horn relay post?? Can you use it as a power feed to a stereo amplifier pulling up to 20-25 amps? It is a 1972 chevelle SS. The horn relay is behind the brake booster. Help do not want to damage the harness!! Thanks for any help!
Gary
 

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you should hook a high powered stereo directly to the battery and fuse it
there are many other ways if you want it switched with the ignition but that would require a relay
 

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Discussion Starter · #3 ·
Tom thanks for the reply, I did not want it hook directly to the battery. Because it would be visable and my SS is a show car.That why I hooked it to the horn relay then through the firewall. You think it will damage OE harness are there fusable links that feed the horn relay??Help!!!
Gary.
 

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Gary,
I believe, and John Muha will probably chime in here, that in the '72, all power for the car itself is fed from the large terminal of the starter solenoid THROUGH a FUSIBLE LINK. I'm not sure what the current rating of the link is, but I'm assuming it to be around 20 amps. If anything blows, it will be that link...IF it's still "in line" and not bypassed. The downside of having your amp fed from the "main" power feed for the car, is the fusible link could blow while you're tooling down the highway with the stereo blasting....leaving you without any power, AND stranded!
 

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Discussion Starter · #5 ·
Jerry, thanks for the reply that is not cool! Who is the guy you talked about? I guess I should move my power supply? Any one else have any thoughts??
Gary
 

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you can tap the power right from the main lug on the starter
that way it will be easy to conseal and wont run through fusable link
 

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If your SS has a factory amp gauge, you need to connect to the horn relay. If you connect to the battery the gauge will indicate discharge when the sound system is on.

Correction: A factory amp gauge will indicate a high rate of charge, not discharge.

When the engine is running the alternator supplies the current for everything, it connects directly to the horn relay. So the fusible link at the starter is not carrying any added load.

You may already have this covered. Is your alternator good for the increased load? If you have a non A/C car the factory alternator was a 37 amp. Definitely will not handle the load. With A/C got a 63 amp, may have trouble keeping up with the A/C running and lights on. If you have already upgraded to a 100 amp or higher you may also want to increase the size of alternator output wire. From the alternator to the horn relay. If this amp is the only add-on your probably ok with the factory wiring, but increasing to a #8 gauge wire won't hurt.
 

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Discussion Starter · #9 ·
Thanks for your replys you say with the engine running the power comes fron the Alt. So it will not pull from the fusable wire at the starter. What if engine is off key on acc. position????
Thanks again hiding the wire is main concern!
Gary
 

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The ignition switch ACC contacts are powered in both the ON and ACC positions on the key switch. Same problem if the stereo is ON and the car is not. If you try and start the car, with the stereo on, you risk popping the link on the solenoid.
 

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I know why beat a dead horse.

Just for the record. When GM added accessories such as A/C, no less than 20 Amps, power windows, power top, power rear window (wagon)... all get power from the horn relay.

I understand Johns concern about the fusible link during cranking\starting. On my ElCamino I routinely start the car with the A/C on and have never had a problem with the fusible link. The factory wiring will handle 20 amps off the horn relay with no problem.

If you often run the sound system with the engine off then I will agree that it's better to connect to the starter. But doing so will drain a battery real quick.

Lastly a factory amp gauge will indicate charge likely about 50 % of scale. It's not a bad thing but should be considered.
 
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