Horn Relay on a 1972 Vette
 

Very quick question:
Is the horn relay under ignition power (on with the ignition) or is it battery power (always hot)?
Thanks in advance.

Always hot.....as it should be.

DUB

Thanks very much. I'm upgrading some of my electrical work in my 72 and trying to do it as safely as possible. DUB, do you suppose you could have a look at a schematic I've drawn and point out any trouble areas I might encounter?
My schematic is a little crude but hopefully, you can tell what I'm trying to do.

https://cimg4.ibsrv.net/gimg/www.cor...9783af73ed.jpg
Thanks very much. I'm upgrading some of my electrical work in my 72 and trying to do it as safely as possible. DUB, do you suppose you could have a look at a schematic I've drawn and point out any trouble areas I might encounter?

https://cimg5.ibsrv.net/gimg/www.cor...58002a9bb8.jpg
The BLUE circle that is around the YELLOW wire at your starter solenoid,. I do not think you need to sue it due to you have a the MSD box being installed. I never have and had no problems with not using it. Power to the coil is coming form the MSD box.

The BLUE circle by your fuse panel. I am concerned about that due to how much power you are pulling off of that terminal in your fuse panel. That IGN terminal in your fuse panel is being protected by the fuse beside it. SO...seeing how you seem to be using this to provide minimal power for the relays it should be fine but I have often times found that I can get that IGNITION power right off of the ignition switch mounted on the column which is protected by the fusible link from the starter. I do not know how mcuh power the vacuum pump is going to draw adn also the stereo.

The GREEN circle around your circuit breaker area is confusing due to I do not know how it is made....I do not know if you have four circuit breaks in there or if there is only one.

AS for the MSD box being protected by a circuit breaker...I know that is the right thing to do to protect the wire but I do not know if that is going to impair the MSD boxes efficiency or not.

I can say that I have had to upgrade the power wire coming off of a starter solenoid and any fusible links that goes to the horn relay due to the massive amount of current I need and what it is drawing through the factory wiring. Sometimes I upgrade the wire from the alternator if I am using it as a area to draw power from also.

DUB

Thanks for your review, I have made some alterations according to your concerns and hopefully I have derailed any future trouble. Please review once again for concerns. I have an exploded view of my circuit breaker box that may add a little clarity to my plans. I have also provided a few links to help understand what I have to work with. The circuit breakers have a shunt (copper bridge across battery side of the breakers) to allow me to use this also as attachment point for other devices. However, I do have some questions concerning the gauge of the wire, at least for what I have planned for now. Here are some specifics for my build:

There are two 40 amp circuits and two 30 amp circuits in my box. These are the circuit breakers:

40 amp - https://www.summitracing.com/parts/b...dback-83635380

30 amp - https://www.summitracing.com/parts/bss-cb123-30hb

Each of the devices has a manufacture part number by them in the event you might want to look at the actual part. Most of this is are Summit Racing parts but I do business with many companies.

I can easily jump from the loaded side of the circuits straight to the MSD and skip the breaker if there is a chance of degrading the charge to the MSD. That is actually exactly what I’m doing for the amplifier although the amp has an inline fuse.

The ignition wire from the fuse panel is basically a trigger wire to the auxiliary fuse panel. This is the aux panel is actually handling the power distribution: https://www.summitracing.com/parts/prf-70207

SIDE NOTE: I have a 140 amp alternator.

The auxiliary panel has a 30 amp circuit breaker built in so just the trigger is all that is needed to rout full power to each device. The vacuum pump has a 6 amp motor with a planned 10 amp fuse (?). The wire to the motor is 14 (I think but can be changed). All advice is welcomed as well as recommendations. I still haven’t purchased the breakers for this build, all other devices i.e.; fans, radiator, relays, aux fuse block, vacuum pump, etc.. are in place. I plan to replace the engine wiring harness and the headlight harness but need advice. I want to upgrade the engine harness for the 140 amp alternator and don’t know if the new factory harness is capable of the higher amps. I also want to upgrade the headlight harness to allow for a full 12v power supply to the lights. There are two separate kits for this purpose, one that attaches at the dimmer switch and another that connects via two new relays, again, I need some advice. Thanks in advance for any help you might offer.
Attached is an updated diagram:
https://cimg3.ibsrv.net/gimg/www.cor...b308ea35b3.jpg

I see you added a 'future fuel pump relay" I would use one of your fuses in your auxiliary fuse panel for that myself to supply power to the coil in the relay and then the actual power to go to the motor you could use the wire off of your circuit breaker box.

Using a 10 amp fuse for the vacuum pump is fine. Remember a fuse, fusible link, circuit breaker are not installed to protect the component. They are there to protect the wire from melting down.

I use two relays when I go and modify the headlight circuit to take the strain off of the headlight switch my self.

DUB

Hey Mitch-

I spoke with Dub- and he asked me to come in and give my opinion. I know- it's free...

First- think of the alternator as your income- and the battery as your bank account- you need to get the income to the bank-

The engineers 50 years ago did NOT design the system to handle an alternator putting out more than twice the current the original one did. Just like instead of 300HP see what happens when you put in 750HP!!!

From the alternator- I'd run 6GU. 8GU would work BUT as a rule of thumb- go up a wire size because of the heat in the engine bay. Running the alt wire- make sure you physically protect and secure it - I'm not a big fan of fusing it- but rather I'd fuse the whole car at the battery (see below). If the alternator shorts out- it'll quit working- not true with the battery

And do realize the Amp gauge will NOT read correctly once you have modded the factory charging system and wiring. That can easily be fixed by replacing it with a Voltmeter- several make one that will match your other gauges.

No need to double fuse the Amplifier- but having a fuse for it is the way to go versus only protecting it with a circuit breaker.. And I would use a fuse for the MSD- like the amplifier- a circuit breaker is not as fast as a fuse - for electronics the slow circuit breaker could easily damage it before it trips.

Also I've attached a headlight relay set up diagram-

And when you do add the fuel pump- Look at a Ford roll over /inertia switch- as it 'll turn off the pump just in case something bad happens


https://cimg6.ibsrv.net/gimg/www.cor...7e507ce7fa.jpg
https://cimg6.ibsrv.net/gimg/www.cor...eb7b15c877.jpg
https://cimg8.ibsrv.net/gimg/www.cor...a66fd622d2.jpg
https://cimg9.ibsrv.net/gimg/www.cor...07fd823297.jpg
https://cimg0.ibsrv.net/gimg/www.cor...8f2a06bfdd.jpg

Thanks for the help. I have again altered my diagram to capture your idea about the fuel pump, but, I have to have switched power for the MSD trigger. I now have the MSD wire attached to the switch wire going to my auxiliary fuse block. Although I already have the Circuit Boss with (4) switched and (3) constant hot wires, I think I may purchase the 7 circuit block with all switched power circuits. This is a link to the box: https://www.jegs.com/i/Painless-Perf...70217/10002/-1 What do you think? It would offer a little more flexibility for my wiring but I'm not so sure it will provide enough bang-for-the-buck in my situation. Here is another diagram for you to skim over when you have an opportunity. Thanks for all your help.https://cimg9.ibsrv.net/gimg/www.cor...1cdb67436e.jpg

Richard454 thanks very much. I have a couple questions (first sorry, I posted my reply to DUB before I realized you had posted a reply) My first question is, should I run from the alternator directly to the starter with a #6? Second, should this be a new wire that bypasses the horn relay? Also, the battery terminal that you pictured, do they have this in a side post configuration? Sorry, I just a wee bit confused. Do you have any idea what size fuse I should use on the MSD? They didn't mention a fuse in their instructions but I agree with you, a fuse would be a lot quicker for protection. The relay for the MSD is a 30 amp - do you suggest a 30 amp fuse? Hmmm, and the headlight diagram shows a fused 12 volt power supply, should this also have a 30 amp fuse instead of the circuit breakers? Thanks for the help.

*****SUPER LONG REPLY*****

Some of this may be helpful and some may be a bunch of BLAH BLAH BLAH

I am going to jump in on this BUT...I hope Richard also replies to give more feedback and his thoughts which are super duper valuable her on the forum.

Having the ability to test and or find out how much amp load a particular component draws is wise to know. So...headlights may only need 15 amp or 20 amp fuse. Calling MSD and asking them how much amp draw their box draws will aid you in putting in a fuse that is slightly over its rating because a fuse is there to protect the wire and not the part being powered. IF a fuse were there to protect a part...then the fuse would be under rated so it would pop when the part begins to get to the point of failure.

Obviously you do know that there are tools that can let you know how much amp draw a part has going to it when it is turned on.

AS for the 6 gauge wire from the alternator to the horn relay....and then back down to the starter solenoid. I am having to say that would be acceptable as long as those connections were clean and tight..

Sometimes my head gets in the way and I over think things way too much and it may be that the 6 gauge wire goes to the starter solenoid directly and then the 10 gauge or possibly an 8 gauge wire is run from the starter solenoid back up to the horn relay to power the system.

I do know that GM did run the wire form the alternator back to the battery directly and ran it inside the frame...and then had a hole in the side of the battery box with a grommet. Whether or not that is the BEST way...I have seen it on some 1980's adn 1981's I believe.

Mitch, I have to say...and not wanting to seen to be condescending...but I am very impressed in your ability to draw up your wiring schematics and the desire to slow down and get everything mapped out before you jump in and install wiring. So many people do not do this ...and often times they have catastrophic results....or IF they need to go back and do a repair ...they can not remember how they wired it due to being in such a hurry that did not even take the time to draw out their schematics for future reference. You would be amazed on the Corvettes I get tor repair where someone previously wired something in and they were so cheap...they bought a spool of blue wire and used it for a ALL of the wiring.

Seeing how you are wiring this up...and NOT that it really matters. Because I know some of these components are already wired in specific colors form that manufacturer who did not care if they match with GM's way. But trying to keep in line with GM philosophy of colors of wires that where used, would or may be helpful.

Basic color chart of wire colors....and the newer the cars get the more wires are added with different colored stripes on them.
*****GENERAL RULE OF THUMB*****
RED is constant 12 volt power that may be fusible link protected
ORANGE is constant 12 colt power but it is protected by a fuse.
PINK is ignition switched circuit with a fuse.
BROWN is ignition switch circuit that is fuse or a protected by the fusible link from the RED wire or fuse
PURPLE is usually the wire for the starter circuit.
BLACK is generally a ground wire.
WHITE is generally used for a switched ground. from like you door jamb switches or headlight switch.
GRAY is generally for gauge or dash lights.
YELLOW is ignition switched with a fuse
DARK GREEN is usually a wire used to send a signal from a sensor to something and on your car is used to power up the horns.
DARK BLUE, LIGHT BLUE, LIGHT GREEN, TAN, are all used for various reasons and can either be a power circuit or a wire to send a ground signal.

So variations such as a black wire with a white stripe can be a wire that is NOT a ground wire but rather this wire is waiting for it to have aground applied to it thus making it a switched wired...so-to speak. When I get into the new Corvettes these various are off the charts but they help when i go to find specific circuit ( light green with a red stripe or white stripe or black stripe) in a huge bundle of wires.

Not knowing if you are aware of any of this or if it even matters but I though that due to you are so serious about this...I would take the time to do this.

DUB

Thank you soo very much, this is extremely helpful concerning wire color and the device protection strategy, and thanks for taking the time to reply. It is important to me and the diagram will depict what is actually done in the car. Please stay tuned to the post, I will be updating the wire color and would appreciate your feedback. I will be purchasing a meter to help me out, the meter that I now have is fried, probably because I haven't used it correctly. Could you offer your advice on a new meter that would get the job done? I may PM you concerning the proper way to use it to keep from killing another one. I'm no electrician, just a DIY'er. I do not have the fuel pump relay yet so I don't know the color of the wires coming out of it but I will be soldering the proper wire colors on all the devices to rout to the power source. Do you imagine any problem using a single switch wire (although I may be able to find another using your wire color legend) to activate both the auxiliary fuse block and the fuel pump? The fuse block switched input is protected with a 3 amp fuse on the block. Additionally, I have a wiring schematic of the electrical system but it doesn't indicate the wire gauge (i.e. headlights, grounds, etc...) Any ideas on how I might get this information? If I can get this diagram right, I would like to share it with others who might have a similar project - if it is deemed valuable. Thanks very much for all the help.

This is not the exact one that I have but mine looks just like it. Simply clamp it over the ground wire to what you want to check and it will tell you the amp draw. Just pay very attention to how they show you to clamp it over the wire due to mine has an arrow made into it that lets me know how I have it rotated on the wire so I know I am clamping over the wire correctly. I think mine is made by MATCO TOOLS.

https://www.northerntool.com/shop/to...yABEgI2K_D_BwE

I do know that some volt/ohmmeters have the provision that can allow you to check amp draw . Depends on how good your meter is and what capabilities it has made into it.

I do not want you to go through a bunch of trouble by cutting wires off and soldering on different color wires UNLESS that is what you want to do. As long as you have the wiring schematic...THAT is all that matters.

If you have concerns that using one wire to power up your fuse panels...you could install a switch that you can turn on and off so that can supply the power to these fuse panels....OR...you can use the switched wire like you plan on using but use it to be the power for the coil in a relay so when you turn your ignition key on it energizes the relay which can then supply the power to the fuse panels you are installing.

DUB

Thanks very much for the link and your advice concerning a relay for the switch power in the aux fuse block is a great idea. I have again altered the drawing to capture the thoughts shared with me. The leads coming out of the box a currently the colors I'm showing in the drawing but I have altered them somewhat to try to be consistent with the wiring legend. Unfortunately, I'm not sure I have it right in my head. Please have a look and let me know what you think. None of the leads are actually long enough coming out of the box so they will have splices. I hope the splices are logical and correct - probably not. Please correct anything you see in error. This is a link to the wiring diagram on the box: https://www.painlessperformance.com/Manuals/70207.pdf
I have also attached another pic of my diagram: I'm still a little confused, should the #6 go from the alt to the starter or to the battery? I believe I'm understanding that it's ok for it to attach to the horn relay as long as it is a tight connection - but - where should it go from there? Thanks.
https://cimg6.ibsrv.net/gimg/www.cor...8c1aab39c1.jpg

For the MSD- its rated at 1 Amp per 1,000 RPM - so a 10A fuse would work.

Circuit breakers are (were?) required by law- so they will come back on if they draw too much current- Depending on you wattage of your lights- I'm running 80/100w low/high and 100w high:D Just take the total wattage and you can figure the current.
That's up for discussion- as several have their opinion- I fused mine -but each bulb filament is fused- so all of them shutting off at one time is greatly reduced (see relay fuse pic below)

OH- do look at the blade fuses that lights up when they blow- will save a ton of time troubleshooting!!!

Just run the alt wire to the starter lug- the car's electrical stuff will still get power from the constant power source with the fusible link from the starter.

You are changing the source of the higher current things ( like the headlights)- I would look at powering the AC/Fan (30A orange wire) off your new circuit beaker panel rather than the original wimpy wiring.

Yep- side post fuse-


https://cimg4.ibsrv.net/gimg/www.cor...8ff0a20364.jpg
https://cimg5.ibsrv.net/gimg/www.cor...244039e7b2.jpg

My fuses & relays tucked up front controlling the headlights and headlight motors



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Man, I love your setup. What headlight kit did you choose? (electric kit)

https://cimg6.ibsrv.net/gimg/www.cor...a817f46101.jpg
The LIGHT BLUE circled area is what is showing me that you have some redundancy here and this wire does not matter any more due to the battery cable going directly to the horn relay buss connection. Or at least it seems to look that way so that wire is not needed and is no longer th ONLY wire doing what it was doing due to you adding the new 6 gauge wire.

The DARK BLUE circled area is raising a slight concern due to JUST MAKE SURE that the gauge of the wire that your fuel pump needs is the SAME as the wire coming out of your relay. Some fuel pumps want a 10 gauge wire even though they only carry 10 amps or so...it is the VOLTAGE drop in that wire that can greatly effect a motor efficiency which is why some external fuel pumps want a 10 gauge wire going to it so the fuel pump can run as designed. THUS the wire from your fused source also needs to be that size also.

As Richard has mentioned ...consider HEAT SOURCES when you are doing this and make all attempts to try to make it so your wiring harnesses are protected from heat if they come close to it.

Do not sweat it if you have one color wiring coming out of a fuse panel that joins to another wire from a relay connector and they change color. AS long as YOU know this and make it in your schematic and where the butt connection is...that is all that matters. I know you can search out an buy these terminal due to that is what I have to do...and I have tackle boxes full of all of the different types of crimp on GM style terminals for basically all wiring repairs. But this can become very time consuming and if that is what you want to do...have at it...but it is not necessary.

When it comes to heat shrink tubing I use some from PANDUIT and also I buy some from WAYTEK.

The Waytek heat shrink tubing I use for butt slices is part numbers 22225,22226 and 22227

https://www.waytekwire.com/

DUB

I make them- shoot me and email and I'll send a PDF on everything that's involved. richard454 at comcast dot net



https://cimg4.ibsrv.net/gimg/www.cor...a06bea7f5a.jpg

This plugs in between the headlights-into the factory harness and controls the motors- don't have to wire all the way to the headlight switch- or swap out to a C4 headlight switch

I also have a relay system designed that you can they open the headlights when you turn them on- but a different sequence when you turn off the headlights. As you turn off the headlights -if you leave the parking lights on- the headlights stay up- to service-clean - be cool- whatever- and then turn off the parking lights they go down- and will only come back up if you turn on the headlights

https://cimg7.ibsrv.net/gimg/www.cor...9e6bc6d76a.jpg

Get yourself one of Richard's headlight kits, you will be glad you did, super simple installation,very well engineered.
Eddy

Emal sent, thanks.