NightshiftHD

Just looking for confirmation I understand this right. I'm adding a couple 30a relays on my headlight motors and a couple more on my high and low beams as I've upgraded to 90/100w bulbs. I've already changed the wires from the original 16/18ga to 12ga and plan to feed power to the relays with a 12ga wire off the alternator.

I know the regulator senses current off the horn relay so this is why one shouldn't feed these relays directly off the battery. I assume the regulator will sense current off the alternator post as well since the horn relay, alternator and regulator are all connected closely on the same wire.

Do I understand this right that it makes no difference whether I feed from the horn relay or alternator directly? Cheers.

Frankie the Fink

If you want you dash gauge to read correctly and charging to be more precise use the horn relay buss. For short term use (headlight motors) its less important than for constant current draws (e.g. headlights, aftermarket A/C). The Mad Electric web site explains all about the 'remote sensing' of the C2 charging systems in their technical section.

NightshiftHD

Thanks Frank. I'll look at the Mad Electric site so I understand this better. I can easily just open the harness further to the horn relay buss and power from there, but I don't understand the need so I will get more educated on this. Cheers, Bill

Frankie the Fink

You don't have to 'open the harness'....just use the main power takeoff for your relays from the horn buss with separate wires (fused of course)... The low power 'triggers' will be the headlight switch and bucket rollover switch respectively.

The headlight relays are easily powered off the floor dimmer switch for both low and high beam. You want minimal voltage drop in the power to the headlights as even a 1V-2V drop reduces their brightness by a double digit percentage..

NightshiftHD

Frank, ya when I said open the harness, I meant to bury my new 12ga relay feed wire in with the existing wires rather than add it on top.

Just read that lengthy write-up from Mad Electric on the topic. In a nutshell for our old cars, the regulator senses voltage at the junction where the wires are crimped together. In my case, powering my relay bank from the alternator post would actually be 10" shorter than feeding from the horn relay buss (ie: 10" closer to the junction crimp). My relay block won't fit on the rad support under the horn relay (BB) so I will mount under the LH fender on the back of the inner fender behind the washer reservoir and run the new 12ga wires from there.

I do realize mounting the relays close to the demand points is preferred to reduce wire length (voltage drop) and maybe if I went with individual relay blocks I could find a closer spot under the front end, but I like this weatherproof Bussmann box so that's why I'm using 12ga wires cause their gonna be 3' longer. Bill

Frankie the Fink

That's a nice distribution box, much like modern cars have

NightshiftHD

I got a 5-relay box in the event I need to power an electric fan since I'm putting Vintage Air in too. We'll see this summer if engine heat is too much. Cheers, Bill