Replacing Headlight relay fusible links with circuit breaker - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 8 (permalink) Old Dec 30th, 15, 10:28 AM Thread Starter
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Replacing Headlight relay fusible links with circuit breaker

I just installed this headlight relay into my Chevelle:

http://www.uapac.com/antique/box-h4-...t.html#q=34263

The kit seems to be of good quality, install was easy, and it made a huge improvement in the brightness of the headlights. Doing further research, however, I've decided that I'm going to replace those fusible links with a circuit breaker.

-- How many amps should the circuit breaker be?

-- There are two relays and power wires, one for the low filament, and one for the high. Can both wires go onto the same post of one circuit breaker, or should there be a separate circuit breaker for each power wire?

-- What is the minimum heaviness of wire that should I install from the circuit breaker to the battery post?

-- I assume that the circuit breaker should have a boot over it. Anything else to protect it?

Thanks for any info.
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post #2 of 8 (permalink) Old Dec 30th, 15, 8:40 PM
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Re: Replacing Headlight relay fusible links with circuit breaker

Need some more info...See my response in bold

The kit seems to be of good quality, install was easy, and it made a huge improvement in the brightness of the headlights. Doing further research, however, I've decided that I'm going to replace those fusible links with a circuit breaker. That's a good idea. Main lighting should not be on a fuse or fusible link where it's "one and done" if something happens intermittently.

-- How many amps should the circuit breaker be?
Upgraded (but stock replacement) halogen lamps? Stock T3's or modern Halogen upgrades that aren't exotic high-end, high current draw will work with a 30 amp automotive self-resetting (type 1) circuit breaker. I recommend the units that have a metal housing versus plastic

-- There are two relays and power wires, one for the low filament, and one for the high. Can both wires go onto the same post of one circuit breaker, or should there be a separate circuit breaker for each power wire? Yes, both main feed wires will connect to the output post on the circuit breaker

-- What is the minimum heaviness of wire that should I install from the circuit breaker to the battery post? Stock set-up Chevelle? If stock, the main power should be connected to the horn relay, not the battery as the horn relay is the main power distribution point. The wire gauge will be determined by how the vehicle is set-up (stock set-up, etc) as length and current both play a role in determining a wire's proper gauge.

-- I assume that the circuit breaker should have a boot over it. Anything else to protect it? Covers "boots" similar to those found on the alternator's rear power connection are never a bad idea. Also pays to take your time and find a suitable location away from excessive heat sources, out of the way so general wrenching on the vehicle doesn't put the wires or breaker in peril and away from any direct water splashes which speeds corrosion.
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post #3 of 8 (permalink) Old Dec 30th, 15, 10:43 PM Thread Starter
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Re: Replacing Headlight relay fusible links with circuit breaker

Quote:
Originally Posted by Coppertop View Post
Need some more info...See my response in bold

The kit seems to be of good quality, install was easy, and it made a huge improvement in the brightness of the headlights. Doing further research, however, I've decided that I'm going to replace those fusible links with a circuit breaker. That's a good idea. Main lighting should not be on a fuse or fusible link where it's "one and done" if something happens intermittently.

-- How many amps should the circuit breaker be?
Upgraded (but stock replacement) halogen lamps? Stock T3's or modern Halogen upgrades that aren't exotic high-end, high current draw will work with a 30 amp automotive self-resetting (type 1) circuit breaker. I recommend the units that have a metal housing versus plastic

-- There are two relays and power wires, one for the low filament, and one for the high. Can both wires go onto the same post of one circuit breaker, or should there be a separate circuit breaker for each power wire? Yes, both main feed wires will connect to the output post on the circuit breaker

-- What is the minimum heaviness of wire that should I install from the circuit breaker to the battery post? Stock set-up Chevelle? If stock, the main power should be connected to the horn relay, not the battery as the horn relay is the main power distribution point. The wire gauge will be determined by how the vehicle is set-up (stock set-up, etc) as length and current both play a role in determining a wire's proper gauge.

-- I assume that the circuit breaker should have a boot over it. Anything else to protect it? Covers "boots" similar to those found on the alternator's rear power connection are never a bad idea. Also pays to take your time and find a suitable location away from excessive heat sources, out of the way so general wrenching on the vehicle doesn't put the wires or breaker in peril and away from any direct water splashes which speeds corrosion.
Thanks for the excellent info. The clarifications:

-- The headlights are standard Slyvania Halogen in the stock housing and wiring.

-- The wiring is stock, more or less. This car has been through decades of multiple owners and the one before me did some shade-tree rigging. I've since cleaned up most of it. There are relays for the starter, and the alternator is a 90 amp one-wire aftermarket set up (works fine with A/C, stereo, ete). The stereo amp has a fused, heavy gauge wire going to the positive terminal of the battery. There will be no more than 2' from the circuit breaker to the power source.

-- As far as the power source, thanks for the tip on the horn relay. I'll dig into the wiring diagrams and set it up that way.

Thanks again for the helpful response. Let me know if the above clarifications bring any other tips to mind.
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post #4 of 8 (permalink) Old Dec 31st, 15, 1:04 PM
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Re: Replacing Headlight relay fusible links with circuit breaker

The factory headlight switch uses a 15 amp thermal overload breaker so I'm not sure why you would need a 30 amp resettable fuse to protect the relay power wire when 15 amps should be enough. Even with the Halogen's you won't pull that much.

Maybe Joe can explain the reasoning for this?

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post #5 of 8 (permalink) Old Dec 31st, 15, 6:11 PM
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Re: Replacing Headlight relay fusible links with circuit breaker

Quote:
Originally Posted by 65chevelle300post View Post
The factory headlight switch uses a 15 amp thermal overload breaker so I'm not sure why you would need a 30 amp resettable fuse to protect the relay power wire when 15 amps should be enough. Even with the Halogen's you won't pull that much.

Maybe Joe can explain the reasoning for this?

Sure.

This isn't the factory configuration. Power is tapped from under the hood with the assistance of relays, thus the voltage level seen by the lamps will be higher. An increase in voltage results in an increase in current with the incandescent lamps.

About 2 years ago or so, I did some current measurements with the modern Wagner "drop in" halogen replacements. (This is for a factory 4 lamps system, the outer bulbs being both hi/lo combination units and the inners being HI only, with all 4 units illuminating in hi beam mode)..,

I used a fully regulated DC power supply with the voltage set at 13.3 volts. Higher then a stock set-up, but low for many of you out there with revamped electrical systems providing a closer to alternator output level across the lamps filaments (14++).

The Wagner H5001 units (the hi-beam only unit), drew 3.8 amps.

The Wagner H5006 units (the hi/lo combo units) drew 2.78 amps (with the high filament powered).

So in high beam mode, (3.8 X 2) + (2.78 X 2) = 13.16 amps @ 13.3 volts.

For even higher voltages, you're cutting it too close to the 15 amp breaker rating. A real risk is nuisance tripping. Another thing to remember with incandescent lamps is they represent a "cold" and "hot" resistance. When they are first powered, there is an in-rush of current as they look almost like a short to a power supply. Once the filaments warm, then the current levels decrease.

Low beam only H5006 units drew 2.8 amps. Low operation would result in 5.6 amps @13.3 volts.

Now, if the OP once to install (2) 15 amp breakers to protect the hi and lo feed lines to feel better about redundancy, that's up to him. I recommended the single 30 amp to cover the needs of the circuit as a whole. The 30 amp breakers with terminal mounting studs and mounting tabs are easier to come by at the local parts stores then say a 25 amp unit.

Back to one of the other original questions on wire gauge, the OP states that the longest run shouldn't be more then about 2 feet. You could use no smaller then a single 14 gauge wire to meet the needs of the whole circuit (main hi/low feed) and be okay.
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post #6 of 8 (permalink) Old Dec 31st, 15, 6:26 PM Thread Starter
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Re: Replacing Headlight relay fusible links with circuit breaker

Thanks again for the information, Joe. I got the 30 amp circuit breaker and have the protective boot on order.

One more question: I trust your recommendation to connect to the horn relay instead of the battery's positive terminal. Is it solely to keep the battery from getting cluttered with connections, or are there other reasons?
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post #7 of 8 (permalink) Old Jan 1st, 16, 9:19 PM
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Re: Replacing Headlight relay fusible links with circuit breaker

With the factory set-up, the horn relay's outer screw connections became a power distribution point for the vehicle. Rather then just having the alternator connect to the battery, the alternator's output line was connected to the bundle of 10 ga. red main power wires that linked up at the horn relay. The battery's "charging line" was a 10 ga. red that ran across the radiator support sheet metal from the battery terminal block (right behind the battery, which linked the 10 ga. red to a 14 ga. fusible link with then went to the battery (+) terminal). This line was to "limit" charging current to the battery, while the output of the alternator was positioned where it was needed most--the splices that fed the main vehicle loads.

Mark at MAD summarized the set-up in his site:

http://www.madelectrical.com/electri...evymain1.shtml

http://www.madelectrical.com/electri...evymain2.shtml

http://www.madelectrical.com/electri...evymain3.shtml

One wire alternator vs. three wire units:

http://www.madelectrical.com/electri...hreewire.shtml


Main navigation page:

http://www.madelectrical.com/electrical-tech.shtml
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post #8 of 8 (permalink) Old Jan 3rd, 16, 11:39 AM Thread Starter
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Re: Replacing Headlight relay fusible links with circuit breaker

Great post, Joe. Thanks again.
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