Main Fuse and relays in SIII?

[printjunky]

I'm just about to wire up my 4 headlights (IIA breakfast in a 74). I was happy to discover (just now after 2 years of working on it!) that they're all already switched over to halogens. But the point is, I'm going to relay them, and I have a few questions I haven't found answers to searching the forums.

First, I need a relay for each dual filament bulb, right? So, in my case 4 relays. Or can I double up and still do a right/left?

Second, can I run one big, fused power wire to all the relays (and how do I split it?) or again, can I double up, or do I need to run 4 power wires?

Anyone know offhand a relay block I can pull from something that has banks of 4, similar to Teri Ann's Terminus El Dorados with the bank of 3? (http://www.roversnorth.com/forums/showthread.php?t=8969&highlight=main+fuse)

Separately, but related, has anyone grafted a main fuse/fusible link or circuit breaker circuit onto the harness? Is there a part of the system I'm not seeing that negates the need for this type of thing? Any opinions?

I've seen few instances of news of fried Rovers out there, so maybe it's a fool's errand. Though I do remember driving from Phoenix to Chandler when I lived there in the 80s, in my 65 Mustang, when a high-current wire shorted to a heater control cable. That cable got RED hot! Didn't burn to the ground, but I never quite got the harness back into shape after that. Freaked my girlfriend out, too!

[bobzinak]

I upgraded my headlights to hella with 80/100 watt bulbs. not exactly legal output levels for the states but in alaska with 24 hour dark and lots of moose on the roads its really nice. I put in a relay I ordered from (dare I say it), J.C.WHITNEY. it was a headlamp relay, one unit 40 amp fuse built in, used the original high beam, low beam wires to activate relay and ran a large gauge wire from the battery and upgraded the wires to the head lights, puchased a new headlamp plug at NAPA, that was five years ago. still works fine. when I had the original lamps in (i think the were like 55/80/ watt) I used a diode to jump the high beam to the low beam so the high beam and low beam were both on at the same time. worked good until I upgrade the bulbs and the bulb life was severly dimminished. to much heat for the high output of the 80/100 bulbs. never any wire melting. I thought that putting in many relays was a pain. you can get hella relays that switch output contacts that are 40 watt relays. so it would be just one relay. much easier to return to original than massive wiring modifications... k.i.s.s. "keep it simple stupid" wiring up four relays takes up room and with heavy wire can be a problem. just my two cents....bobzinak

[Jim-ME]

When I installed my halogen headlights I added a new 6 slot fuse block under the bonnet mounted to the bulkhead which is wired directly to the battery. I built two new three wire harness to run from each relay to the separate headlamp circuits. Two of the wires are power out of the relay to each headlamp and the third is connected to the original factory wiring up front to turn on the respective relay when I turn on the headlamp switch or use the dimmer switch for high beams. I only used 2 30A relays; one for low beam, one for high beam each on it's own separate circuit out of the new fuse block . Since my headlamps are the 50 state legal ones I felt that 4 relays was excessive. I used stock Lucas bullet connectors for all headlight connections so that if someone else didn't like the upgrade it could easily be put back to stock. I crimped both the low beam wires together at the relay so that there would be one wire to each headlight and did the same for the high beams. I also used the "correct" color coded wiring so that if anyone needs to chase an electrical headlight fault they can refer to the green bible for color codes and hopefully it will make sense. The only thing I did that wasn't stock was to change the front ground at the breakfast to a ring terminal instead of using the bullet and clamp that was there originally to make sure I always have a good ground.
Jim

[kevkon]

When I installed my halogen headlights I added a new 6 slot fuse block under the bonnet mounted to the bulkhead which is wired directly to the battery. I built two new three wire harness to run from each relay to the separate headlamp circuits. Two of the wires are power out of the relay to each headlamp and the third is connected to the original factory wiring up front to turn on the respective relay when I turn on the headlamp switch or use the dimmer switch for high beams. I only used 2 30A relays; one for low beam, one for high beam each on it's own separate circuit out of the new fuse block . Since my headlamps are the 50 state legal ones I felt that 4 relays was excessive. I used stock Lucas bullet connectors for all headlight connections so that if someone else didn't like the upgrade it could easily be put back to stock. I crimped both the low beam wires together at the relay so that there would be one wire to each headlight and did the same for the high beams. I also used the "correct" color coded wiring so that if anyone needs to chase an electrical headlight fault they can refer to the green bible for color codes and hopefully it will make sense. The only thing I did that wasn't stock was to change the front ground at the breakfast to a ring terminal instead of using the bullet and clamp that was there originally to make sure I always have a good ground.
Jim

Ditto here. I also got a fuse/relay power center out of a junked Disco which I may use in the future.

[printjunky]

It may be moot, as the halogens have some other wiring on them, and I'm not sure I'll be inclined to change that, but where did you get the original coloured (sic) wire? Our hosts, likely, but I can't find it.

I do plan to leave the original bullets intact and go from there to the relayed looms for possible future reversals (there will be no next owners. Bury me in the thing!)

[printjunky]

Oh, and Jim, the reasoning behind my 4 relays question, is that I have 4 headlights.

Did you put any kind of main fuse/breaker between the battery and the new fuse block?

[Jim-ME]

I got my wire from British Wiring in PA and bought it by the foot. I also got crimp style bullet connectors which some don't approve of but I have the bullet style crimping tool and haven't had any issues. If you use the crimp style bullet connectors I'll offer the loan of my tool since they aren't cheap. If you plan to run both sets of headlamps on both low and high then you would need 4 but I'd think that you would really PO on-coming traffic because it would be too bright. Id throw out that you consider low beams in one location high beams in the other or dual beam in one location and high beam only in the other. If you go the second route you would need three; the first route only two. I fused the new fuse block with a 30A inline blade type fuse. If you think you are going to draw more than 30A at one time out of the new fuse block you would need to move up to a maxifuse which is what I had to do when I put in a 70A relay and used a 50A maxifuse for my glow plugs. IIRC my maxifuse holder alone was $25.
Jim

[jac04]

I also got crimp style bullet connectors which some don't approve of but I have the bullet style crimping tool and haven't had any issues. If you use the crimp style bullet connectors I'll offer the loan of my tool since they aren't cheap.
Jim-
I'm getting ready to install headlight relays on my Lightweight. Drove it the other night and the headlights dimmed every time the turn signals flashed.:rolleyes:
Anyhow, I'm planning on using the factory type bullet ends on the wiring since I already have the bullet ends and want everything to be a simple plug-in. I have always soldered the factory type bullet ends in place. What type of bullet connectors did you use?

[jac04]

Also, in case someone is looking for a simple plug & play harness, SMS has some reasonably priced options at:
http://www.rallylights.com/SMS_Custom_Wiring_Harnesses.aspx .

They are also an excellent source for high-quality bulbs and pretty much anything else that you might need.

[Jim-ME]

I used the ones from British Wiring that could be crimped or soldered.
Jim

[jac04]

I just finished installing my headlight relay set-up. I used the Hella relays with a built-in 25A fuse to keep things simple (RN p/n 87204 for $10.50 each). All I can say is Wow, what a difference! No more dim headlights. No more headlights dimming as the turn signals blink. Well worth the time & little bit of money. :thumb-up:

[printjunky]

Ok, this is my design at this point. See any wrinkles? Any improvements or recommendations?

Know the answers to any of my questions? I have some pretty good knowledge about wire gauge and ampacity. just looking for a little confirmation. 5,499 (no. of members) brains are better than one!

[printjunky]

Just realized that for the switch, I'm using the existing wires, so I'm good there.

[mongoswede]

Voltage = Current x Resistance (E=IR) Wattage / Voltage = Amperage. So a 100 watt driving light draws between 7 and 8 amps depending on your alternator output. 100Watts / 12.6 volts = 8 amps.

[printjunky]

Yup. 65w/55w high/low, 13.5v (GM alt).

[Jim-ME]

I used 28 strand wire which is equivalent to 14 ga. US. Each wire is capable of taking 17.5A. When I ran my calculations I figured that both high beams on would draw 12A and the low beams would draw 10A. I want my fuses to be the weak link in my wiring so my low beams are fused by a single 10A fuse and my high beams are protected by a single 15A fuse. To date I haven't blown either. IMHO your fuse ratings are way high and will not protect your wiring, relays or headlights should something go south. I'd rather blow a fuse than see smoke. Just my 2 cents.
Jim

[jac04]

I'd rather blow a fuse than see smoke.
Good point, Jim.... I'm off to swap out those 25A fuses in my Hella relays.

[mongoswede]

Good point, Jim.... I'm off to swap out those 25A fuses in my Hella relays.


odds are there are 25A fuses in those hella relays because they are anticipating someone running a pair of 100 watt driving lights (200 watts) off of them.