Upgrading Headlights This Weekend

[Bruzilla]

Looks like I'll be spending another weekend under the hood. I just ordered two relays for the headlights and they should be on the deck Thursday or Friday. Time to get some wire and accessories and upgrade the high and low beams to relay set-ups, then I finally get to put the modern halogen lamps in.

 

[RustyRatRod]

http://danielsternlighting.com/

 

[Bruzilla]

I've read that article before, but there's one thing I don't get. He states you should get the power for the lamps from the power output on the alternator because that's the only way to totally isolate the car's stock wiring. But, if I go from the battery positive terminal, how am I not accomplishing the same thing? Doesn't the output stud on the alternator connect to the battery cable? So what difference does it make if I'm connected to the battery terminal directly or via the alternator power output stud?

 

[RustyRatRod]

It's not just an article, it's his whole site. Surf about it. Send Dan an email. He's a damn fine fella and will hook you up. As for your question, hell if I know. lol

 

[Bruzilla]

Yeah, I like his site, but his is the only one I've seen make the contention to pull the power from the alternator, but when you do that you're really not actually isolating the draw from the car's wiring since the relay source wires are connected to the same point as the battery cable, so I don't see any benefit to drawing from the alternator.

My plan is to mount a two-fuse block to the fender near the battery and do a tap from the battery positive to the block, then from the block to the relays. That'll also keep the wires runs as short as possible.

 

[kursplat]

when you pulling the power from the battery the alternator still has to charge it, through the bulkhead connector, through the ammeter and back out the bulkhead connector. it's not like he doesn't know MOPARS. there is also the MAD-ELECTRIC way of doing it, which to me looks a lot like a hack job, but some people do it and get by.

http://www.slantsix.org/forum/viewtopic.php?t=18493
another good electrical read ^^^^^

 

[Bruzilla]

According to his article, you can run the headlight power direct from the positive battery terminal to the relay, or his recommended way, from the power output on the alternator to the relay. But since the power output of the alternator is connected to the battery from the exact same point the power outputs to the relays are connected to, the relays are essentially connected to the battery and there is no separated, isolated, circuit for the headlights. The only difference is the relays are connected to the battery via the battery cable vice directly at the battery post. If there were two outputs on the alternator, with one going to the battery and the other to the relays, I could see that taking all the load off the charging system completely... although you would only have headlights when the engine was running.

The other end of the cable is attached to the positive battery post. So whether I attach the power output to the relays at the alternator end of the cable, or the post end, there's really no difference since it's all the same circuit. It's not like the current is going into the battery and then out of the battery and down the wires to the relays. The relays are getting the same current as the battery is getting right?

 

[RustyRatRod]

Sure there's a difference. One way attaches to the source of power directly, the other attaches to the battery and does NOT see alternator voltage.

 

[Sprag]

Despite convention wisdom, I believe that powers flows FROM negative TO positive in a basic DC circuit and as such, the high current side of your new circuit(s), when wired as Dan recommends, will be completely isolated as power flows from your new ground(s) to the alternator 'batt' stud and no further. To me, it would make no matter what is on the other side (after the alternator 'batt' stud) so long as everything is in good working order (not shorted, overloaded, etc) and the last place I seek to take additional + taps from is the already crummy battery post/clamp arrangement.

 

[kursplat]

to really see the full affect you need to get beyond thinking about just the headlights. there are some good articles at slantsix.org and forabodies only about bypassing the ammeter by wiring directly from bat+ to alt+ (with appropriate protection). part of what your trying to do is stop the load from going through the bulkhead connector and ammeter, like a modern car, with relays and fusing in the engine bay. stock ALL the headlight current goes into the crappy, old, brittle plug at the firewall and then to the headlight switch. that's a lot of load for some really old contacts. anything you can do to move that load is a good thing. but you want to use proper wire size and fusing.

good luck

 

[RustyRatRod]

Yeah.....Dan is an electrical engineer. It's what he does for a living. Trust me, he's right. Just ask him. lol Seriously, Dan's an awesome guy to have in our hobby. He is a wealth of knowledge and always willing to share it.

 

[Bruzilla]

Sure there's a difference. One way attaches to the source of power directly, the other attaches to the battery and does NOT see alternator voltage.

I would agree with you if there were an isolated circuit involved, but there isn't. The cable from the alternator output post connects to the battery positive post. That's a circuit. When I attach the relay power wires to that same output post, they are also in contact with the battery cable, which connects them directly to the positive battery post. There's no switching going on at the alternator to source power just to the relays, and there's no isolated circuit for the relays. By connecting the relays to the alternator post, they become part of the alternator to battery circuit, and by connecting the relay wires to the battery post they are part of the exact same circuit. So aside from the corrosion issue, there's no difference in current flow or impact on vehicle wiring as the only vehicle wiring being impacted is the cable from the battery to the alternator.

 

[kursplat]

The cable from the alternator output post connects to the battery positive post. That's a circuit.

it is, but it's a crappy circuit because the whole thing runs through the fuse link, along with everything except the starter relay and starter. just adding a relay run from the battery does takes load off the headlight switch. but the headlight load that gets taken from the battery is still being replaced by the alternator, via the stock wiring, fuse link, ammeter, bulkhead connector, ect.
i hope this isn't sounding like a dump on Bruzilla thread, i think everyone just wants you to end up with something your happy with

 

[RustyRatRod]

Naw, ain't tryin to dump on anybody.....in fact, I'm electrical stupid. BUT, I know enough about it to know there's a voltage drop between the alternator and battery. This is the whole point of Mr. Stern's kits. To get alternator voltage to the headlights so you can actually SEE.

 

[72RoadrunnerGTX]

The cable from the alternator output post connects to the battery positive post......
there's no difference in current flow or impact on vehicle wiring as the only vehicle wiring being impacted is the cable from the battery to the alternator.

Assuming your vehicles wiring is original, this simply isn’t true. As already mentioned, the connection between the alternator output post and the positive battery post contains several points of resistance that create voltage drop, bulkhead terminals, loose amp gauge studs & nuts, fusible links and their terminals, not to mention the relatively small 12ga wiring used in between. As has been proven, over time with these cars, this resistance only increases with age as corrosion sets in. Every amp of load added to the battery terminal is replaced immediately by additional alternator output through the above mentioned terminals and wiring in the charge circuit. Still don’t believe it? Your amp gauge will show this additional load to you if you add load to the battery side of the amp gauge. BTW, by design, all of the vehicle's existing electrical load is connected on the alternator side of the amp gauge, not the battery side.

If you don’t want to add to or impact the electrical load on your existing charging circuit with your headlight upgrade, connect this additional load to the alternator post, just the facts.

 

[Bruzilla]

Okay, now I get it. I was looking at the first diagram he has on his site, which matches how my Fords are wired up, which was what was throwing me. I'm used to a more direct connection between the battery and the alternator. I just went out and looked at the stock wiring in the road runner and I can see where it's different.

So my new question is, if I wire to the alternator, do I still have headlights when the engine isn't running?

 

[Richard Cranium]

These headlights work for me................

 

[RustyRatRod]

So my new question is, if I wire to the alternator, do I still have headlights when the engine isn't running?

You betchya.

 

[TheSwede]

So my new question is, if I wire to the alternator, do I still have headlights when the engine isn't running?[/QUOTE]

Yes.

 

[RustyRatRod]

What are you using for a harness?