Wiring question

[GeorgeLeonard]

As this question will indicate, I dont know much about automotive wiring. I recently purchased a 1966 Chevy truck project and the wiring is a mess so I am sure to learn a few things while trying to figure it out. The guy I bought it from used to connect the battery terminals every time he used it and disconnect the terminals whenever he turned the engine off. He said that the battery would drain if he didnt do that. Whatever.

But he told me that when re connecting the positive terminal, to be sure that I also included a certain red wire which he showed me. Fine. I do exactly what he told me and everything is as it should be- starts and runs no problem. When I dont connect the red wire- it will not start. So Im curious and I start to look around and see the red wire is hooked up the the horn relay? So I look at the wiring diagram and see it is supposed to be just that way- this seemingly life giving red wire is connected to the horn relay. It just seems so counter intuitive that such an important wire would come from the horn relay. Can someone make some sense of this for me? As anyone who must be considering answering this question must already know, it goes from the horn relay to the voltage regulator and then to the alternator.

Why would this wire stop my engine from starting? What does this wire really do? Or are things more messed up than I think they are? The good news is that when the wire is hooked up to the battery, it starts and runs pretty good. Has it been hot wired or anything like that?

[broey]

does the horn work? is there a chance he is using horn relay for something else?

[cb1965]

I believe thats the wire that feeds power to your fuse box and everything else
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[GeorgeLeonard]

It would seem so. But how can such an insignificant looking wire do so much? I know thats a stupid response but it just doesnt look right to me. Im 65 years old and Ive been a car guy all my life. I just dont remember another car being like this? Am I right or am I crazy?

[protrash64]

The relay is merely a stopping point on the way to the fuses under the dash. The power eventually goes to the key which allows you to start the truck.

[6tfo]

This is how I see it. One of the red wires off the Horn relay then goes to the connector at the firewall. On the cab side of the firewall connector that red wire turns into a brown wire with a white stripe. The brown white stripe wire then goes to your ignition switch. So I'm thinking the brown and white wire is your primary power to your ignition switch. It seems like the Horn Relay also acts as a junction for the hot wire. Why'd they pick the horn relay, don't know.

[chopper john]

it powers the fuse block.

[PGSigns]

My 65 was such a mess I just put an American autowire harness in it. When I got trying to clean up the 45 plus years of chopping and cutting it was easier to just fix it right and replace the entire harness.
Jimmy

[neto]

Chopper john is right. It powers the fuse box. That wire should connect to the second prong on the horn relay not the two connections under it for the horn. I just fixed some wiring on my 63 and it was fun cutting all the extra wires and "wing nuts" I found.

[GeorgeLeonard]

Okay, far be it from me to tell GM how to build a truck. But Im looking at the huge, herking battery cable that goes from the positive pole on the battery to the solenoid/starter to do the heavy work of cranking my engine over in the morning in all kinds of weather. That makes sense to me. But the rest of my trucks electrical system comes out of that puny 12 gauge red wire that is draped across the front of my radiator? I realize now that that is the way it was designed and that it seems to work but somehow it just doesnt seem adequate to do such an important job. Im thinking that the first thing one should do when acquiring a truck like ours is to inspect that wire, maybe replace it with something heavier, clean up all the terminals where it stops along the way, and maybe even insulate it further from any heat sources that it may come up against.

Im probably wrong but it still seems to me to be a cheap ass way to design a truck.

[lakeroadster]

Originally Posted by GeorgeLeonard

As this question will indicate, I dont know much about automotive wiring...............

Originally Posted by GeorgeLeonard

Okay, far be it from me to tell GM how to build a truck. Im probably wrong but it still seems to me to be a cheap ass way to design a truck.

Gee George, you admit you don't know much about wiring, yet you go about ripping GM a new one?

• The big cable feeds power to the starter, the biggest amp draw in the entire circuit.
  
• The little red wire powers the ignition switch, not a very big amp draw.

Wires are sized based on their required current carrying requirements, not their importance. And they are routed to provide power, but to do so in the shortest distance possible.

I guess I don't understand the negativity toward GM. Sounds like the PO did some stupid stuff, put the blame where it belongs. As has been said before the wiring harnesses in these trucks have worked flawlessly for over 50 years as long as people don't screw with them.

Nothing wrong with disconnecting the cable, makes the battery last longer on a truck that isn't driven much. One thing to note however: You should be removing the ground cable, not the positive one.

Why not attach the little red wire and the starter cable to the battery and then get a battery terminal ground power disconnect? Then you simply can turn the switch instead of removing the battery terminal. That should get you by until you tackle redoing the wiring.

Check out this link: http://www.griotsgarage.com/product/...ct+terminal.do

[6tfo]

Hope I don't sound like a smart$%& but look at it from a positive side (pun intended), if it breaks it's easy to find. Think about having to troubleshoot wiring on a new truck.

Having one of these trucks for over 20 years I've never had a problem with it. Not sure why the previous owner had to disconnect it to keep the battery charged. Is that normal or could there be other issues would be my question.

[GeorgeLeonard]

Well, not knowing anything about it and being a naturally curious person, sometimes to my profound detriment. this is what I did: I took a 12 volt light bulb and dug the base into the positive pole of the battery. Then I took the infamous "red" wire and and touched it to the side of the bulb and it lit faintly. Using my powers of deduction, I decided that the red wire must be providing some sort of ground or else the bulb wouldnt be lighting at all. So great, now I know I have a short but who knows where?

As I said before, this trucks wiring is a mess so I just figured Id start disconnecting things until the bulb stopped glowing. Again, my intuition kicks in- do the simple stuff first. So I removed one stop/turn signal rear bulb and nothing happened. But when I removed the other stop/turn signal bulb my test bulb went out. Lucky for me, I think I hit it on the second try!. All that remains now is to leave the battery connected all night and see if it drains.

[6tfo]

Keeping it technical. After looking at the wiring diagram this morning the red 12 gauge wire goes into the cab where it is spliced feeding direct power to the fuse box, headlight switch, and the ignition.

Since it feeds direct power to those 3 items, most importantly the fuse box, I would say it essentially powers everything accept the S/S. I'm no expert but that's how I see it. So when you disconnect the red wire as to not drain your battery you should loose everything. Does that answer your question?

[bundeber]

George, Yes that 12 gauge wire runs the rest of the trucks electrical systems. Like was stated earlier, this wire feeds power to the whole vehicle, and the amperage for all of your wiring will easily be carried by that 12 gauge wire. This system is designed so that even if all your electrical stuff is on at once, there is still sufficient room in the wiring that the vehicle won't blow a fuse or melt that wire down.

I know it seems like it's small to run all the electrical, but trust me, ANY automotive brand will do anything to avoid recalls. This costs them literally millions of dollars, if they weren't sure of the wire size they wouldn't have put it in. And as was stated, these systems have worked near flawlessly for 50 plus years. As long as some nucklehead hasn't butchered the wiring you should be fine.

By the way, it sounds like something has been hooked up on yours incorrectly. By this I mean that I believe someone hooked something up to a wire that has current all the time instead of a wire that has current when the key is on. Does this have a newer stereo with a clock on it or some sort of electrical add on that has memory? And just how long does it take for the battery to drain.

ALSO, that little red wire connects to the fuse panel, but it also powers the ignition switch, the ignition switch needs 12 volts in order to engage the solenoid which engages the stater motor. That's why it won't start without that wire being hooked up.

Hope that helps.

[GeorgeLeonard]

Well, I guess I have my answer but I still find it hard to believe that that puny red 12 gauge wire can carry current for everything else: That would be windshield wipers, horn. headlights, parking lights front and back, stop lights, turn signals front and back, interior lights, glove box light, radio, heater fan, possibly air conditioning, cigar lighter, dash lights, back up lights, ignition, emergency flasher, and anything else I may have forgotten.

Wouldnt you at least agree that that is an awful lot for one wire to carry if they were all turned on at once? And does that allow for a normal margin for error including the fact that some yahoo may hook up another accessory that he just has to have?

I just think a heavier wire may be called for espeically in view of what some people are now adding to their trucks.

[bundeber]

I know this is confusing, but you have to consider the fact that you're running a 12volt system. Just because in a house you can run a 20 amp appliance and pop your fuse does not mean you're limited to 20 amps on a 12 volt DC circuit.

Because cars are direct current, it means that the electrons travel the entire length of the wire, they are not bouncing back and forth being excited like the electrons in home wiring. The other thing to consider is that electricity is mostly carried on the surface of the wire. There is much more surface area in a multi strand automotive wire than there is in a solid 12 gauge wire for a home. Meaning electricity is carried with more efficiency.

While I'm clearly no expert! I do know that in a vehicle, because of the low voltage the heat generated in a wire is much less than in a house. For this reason you can carry about 60 amps on a 12 gauge wire. You can use this formula to figure out what your approximate amp draw is on each segment of your system.

For example.... Your headlights are probably rated to 35 watts. W/V=A
This means your headlights on high beam draw just under 3 amps. Even if you added up your stereo, wipers, lights, turn signals etc... you still aren't going to approach the 60 amp limit on that wire.

[GeorgeLeonard]

Okay, that sounds good to me. I will stop worrying about that wire now and go on to other more pressing concerns. Thanks for your answer.