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Horn Relay vs 50A Fuse

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Twstnshout

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Getting ready to register my BN2 for the first time since 1969. Last thing to attend to was the horns. Of course neither one worked so I ordered one reproduction just to pass inspection. Kept blowing the fuse. I think I finally eliminated the ground short. I’d like to install a relay and eliminate the silly 50A horn circuit. Is that reasonable to install a later Healey relay in a '55 BN2?
 
Twstnshout said:
Getting ready to register my bn2 for the first time since 1969. Last thing to attend to was the horns. Of course neither one worked so I ordered one reproduction just to pass inspection. Kept blowing the fuse finally think I eliminated the ground short I think. I’d like to install a relay and eliminate the silly 50 horn circuit. Is that reasonable to install a later healey relay in a 55 bn2?
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The same "silly" horn circuit is in all later Healeys. You could install a relay, but the horn circuit should still have a 50-amp fuse.
 
The relay won't eliminate the 50 amp circuit, it would only eliminate the high current draw from the horn going through the trafficator switch on your steering wheel. The horns draw what they draw. While I've never been a fan of the way load current goes through all the switches on my BN2 I haven't put in any relays. It certainly isn't a bad idea. You also should consider that the relay switch power needs to be fused. I do have LED head lights mainly for load reduction. Relays didn't really come into use until the early 60's in a lot of cars and I'm sure there were less fires and melted wiring as a result of using them. I would not remove any fuses and a relay doesn't replace those. In fact, adding fuses to circuits is worth doing. Before I dropped a 5 speed in mine, I had an additional in-line fuse for the OD relay as it has been a problem others have experienced. Maybe someone knows what a proper functioning horn actually draws, I suspect ( hope) it is much less than 50 amps.
 
Separate all your wiring circuits , protect your wiring harness and fuse items individually .
Easy to do parts on Amazon for $30 or less .
 

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I am a believer in protecting circuits separately.
The 50 amp fuse has always seemed rather primitive to me and to my mind you may as well be using a 16D nail.
 
Well I guess I'll be the contrarian again. But first I will say the splitting up your individual circuits is a good idea just for convenience of trouble shooting if ever necessary. But the fact that you have multiple circuits being fed by one fuse is really not unsafe. It just mean that the fuse is operating at closer to its rating. And with that any small overload or short circuit current will readily blow the fuse quicker. To troubleshoot a situation where many circuits are fed by one fuse and the fuse blows, you just lift off all the circuit wires from the fuse holder and then apply them back on one at a time to see which one blows the fuse then you have your errant circuit. Granted if you have a low current overload individual fuses that are matched well to the load they supply will make troubleshooting the problem quicker. Another note is that the 50amp fuse that the horns are connected to was also intended to supply any auxiliary equipment that might be installed on the car. Such as radio and fog lights.
About relays. I have never been a strong proponent of more relays. One reason is that if you have a vehicle that has had the circuits in place for the last 50 or so years and has worked very well that way why do you believe now the car needs relays. But yes relays are sometimes needed when you install a new device/component that pulls exceptionally high current. Such as these aftermarket electric engine cooling fans. They can pull upwards of 20amps and in many cases will burn out hand operated switches. Also at 20amps you need to supply the fans with heavier wire so think about where your going to connect that to. If your still running an original generator, good luck as the original generators were only rated for about 15 or 20 amps total. One last thing about relays, if you are adding them where they are not needed then all you are doing is adding complexity and more wire to your car.
 
"the fact that you have multiple circuits being fed by one fuse is really not unsafe."

But quite inconvenient when your heater fan takes out your fuel pump. :smile:
 
That’s a good point Michael. That’s why I have two fuse boxes in my Healey. On is for “ignition on” circuits and the other is for “ignition off” circuits. Please don’t ask me which circuits I put in which box, it’s only been 20 years since I did it. 😁
Still no extra relays.
 
Jack, the only concern that I have ever had about the head light circuit is that on the original configuration the headlight circuit is not fused (if I remember right). This is a bit dangerous as once a Sprite I was working on shorted at the dimmer switch and it almost smoked the whole car. Now fusing it and putting it on relays is two different things. It has been the opinion of the intelligentea that current load of the headlights will burn out the switch and dimmer switch. Yet for 50+ years it has not on most cars. It certainly has not done it on my car in 60+ yrs and 100+ kmiles.
But I’ll concede that a 60 year old switch might fail. But not often enough for me to add all that extra wire and then a couple more components called relays. Maybe the relays will fail???
 
vette said:
Jack, the only concern that I have ever had about the head light circuit is that on the original configuration the headlight circuit is not fused (if I remember right). This is a bit dangerous as once a Sprite I was working on shorted at the dimmer switch and it almost smoked the whole car. Now fusing it and putting it on relays is two different things. It has been the opinion of the intelligentea that current load of the headlights will burn out the switch and dimmer switch. Yet for 50+ years it has not on most cars. It certainly has not done it on my car in 60+ yrs and 100+ kmiles.
But I’ll concede that a 60 year old switch might fail. But not often enough for me to add all that extra wire and then a couple more components called relays. Maybe the relays will fail???
Click to expand...
Daniel Stern presents a compelling case for relays in the lighting circuit. I’ve driven a lot of miles at night in these 60s era cars and will take any improvement I can find. A bonus was sourcing relays with an integral fuse. Often wondered why the Healey lights weren’t fused.
 
Jack T said:
Daniel Stern presents a compelling case for relays in the lighting circuit. I’ve driven a lot of miles at night in these 60s era cars and will take any improvement I can find. A bonus was sourcing relays with an integral fuse. Often wondered why the Healey lights weren’t fused.
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Jack--

I have heard some Icons in the "Healey Repair World" make the same statement and it makes no sense to me either. After (hopefully) locating the source of the problem, instead of having to replace a fuse one would have to replace either the lights or wiring or both.

For almost all of my circuits I have fused relays.
 
Jack, I will have to find Daniel Stern’s article. The idea of non-fused headlights certainly seems strange. It must be that the manufacturers put so much importance on the need to see over and above the fact that you might burn your car down. 🙄.
But I do know that American manufacturers (Chevy for sure) provided a circuit breaker of sort built into the headlight switch. It was a bimetal contact that would open on overload and reset itself when the overload was removed. In essence is that when the headlight circuit shorted the headlights would continually blink. Thereby providing a pittance of visibility to get you home.
 
Jack T said:
Daniel Stern presents a compelling case for relays in the lighting circuit. I’ve driven a lot of miles at night in these 60s era cars and will take any improvement I can find. A bonus was sourcing relays with an integral fuse. Often wondered why the Healey lights weren’t fused.
Click to expand...
On further thought let’s delve into this a little deeper. Assuming we use the same headlights and the power to the headlight is run thru wires that are adequate for the load, why would running the power thru a relay contact vice running it direct to the lights as original circuit does make any difference to the efficiency of the light.
Also, the concept of fusing the lights or not fusing them is irrelevant to the repair of the light if the circuit or lights themselves do short out. You still have to make the repair before you have lights again. Just replacing a fuse on a shorted circuit isn’t going to do anything except blow the fuse again. A fuse in the circuit might contribute to nuisance tripping just like early Ground Fault Circuit Interupter breakers used to trip unnecessarily from minor circuit disturbances.
The validity of a non fused circuit might make sense if you consider that the original manufacturers may have considered that the weak link in the circuit was the bulb itself. With the circuit wires themselves being so robust that it would be very unlikely that they would have a problem. If the filament in the bulbs blow out just change the bulb or disconnect it and be on your way. The only time most wires have a problem is by age or that someone has been messing with them. There are only two other weak links in the headlight circuit. That is the dimmer switch and the headlight switch itself. Them being mechanical moving parts they can and do fail. Adding relays you still have these components as well as adding more - the relays. I do know from experience that the dimmer switch is what I call “Dangerous”. If it shorts out it is all metal and will create a permanent fixed short and all the wires in the circuit including maybe the car will melt down.
So even tho I’ve delved into this from differing angles my main premise is that relays do nothing for the efficiency or troubleshooting of the headlights.
 
One thing you might consider with regard to fuses or no fuses is time. Wires often short out but do not completely melt copper for some period of time during which more insulation melts and what might have been a minor repair with a fused circuit becomes a major repair or even a fire. I'm considering chaffed or damaged wire. I can't count the number of times I've done trouble shooting by putting an in line fuse in a circuit, knowing it would blow until I found where the issue was.
 
Vette--

I agree with Jon. If fuses are blowing in something as straightforward as a headlight circuit it should not take long to visually inspect the wire run for a short, etc and/or replace the bulb plug, etc., even if at the cost of a few fuses blown while trying to pin down the issue. However with no fuse that little kink/chafe in the wire could easily result in having to pull most or all of the circuit because heat from the short melted a long section of the wire, etc.
 
I’ll have to read Daniel’s work before I can agree or disagree with him. Can I say I am an “unrecognized expert” in that I have a pretty good electrical background having worked in electronics in the Navy an spent 40 years with an electric utility. But I don’t know it all. Every system can have its reasons.
I agree an unfused circuit does seem ill rational. I didn’t design it. I think Chevy’s idea may seem the best.

Just a side note to realize. In the electrical construction industry there are some designated circuits that are built “Non-Fused”. These are circuits that are deemed so important that they don’t ever want them to go out. These circuits supply something that is so necessary to the property that only if the property is totally destroyed should they be allowed to not function. An example is main fire pumps in large commercial buildings. Many times the circuits suppling these pumps are not fused. The only way these pumps would shut off is if and when the utility transformer fuses would blow. You can read that in the National Electrical Code if you like. Maybe the designers of LBC wiring had that concept in mind.
Please remember I’m not arguing against fuses. I’m arguing against the utility of relays. But there are places where relays are practical even necessary.
 
Well here goes. I've read Daniel's work and here is my take away from that article.
- I agree that voltage drop can be a problem.
- I don't agree that the original wiring, i.e. wire size is inadequate.
- I can't accept that saying that the headlight circuit was inadequate when new irregardless of it's time in use.
- I say that you can guard against unwanted voltage drop by maintaining good electrical connections.
- Even if you are running an original generator the voltage regulator is designed to maintain the minimum voltage required for the systems and components in the car.
- If you are experiencing voltage problems then you should rebuild or replace existing components in the car such as the generator and voltage regulator as well as maintaining clean quality connections.
- If you have an alternator in your car you will experience less voltage problems than with a generator. But if you do have problems then some component is failing.
- If you "add" electrical "load" (something that draws more current) such as radio/sterio/GPS/Fog lamps/stronger high capacity fuel pump, etc) you can overload your electrical supply (generator/alternator/battery) which will cause a voltage drop and problelms.
- If you change out lights to LED the the LED bulbs draw less current than the original incandescent bulbs did and will have no problem running on original wiring. REMINDER, all original connections should be maintained in good condition.
- I have Halogen headlight bulbs in my Healey. They have been operating on the original design wiring (replaced complete harness when I restored the car 20 years ago) for 20+ years. They were in the car when I bought it so they were obviously running on the original harness.
- Daniel's theorizations about percentage loss of voltage and subsequent light levels is in my opinion irrelevant subterfuge. Your voltage and lights levels he describes should never reach those levels unless you are limping home with a damaged vehicle.
- Daniels's description under the heading "How to Solve Voltage Drop" is really a foray into describing the value of relays. The only problem with his premise is that it isn't necessary. The answer to how to solve voltage drop is to maintain the existing components and connections in any car. I'm sure any mechanic of any era car will tell you that.
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The only reason to ever add a relay is if you are adding a component that draws really high current. An example being many electric engine cooling fans. Also remember when adding a new high draw component you must consider the supply source built into your car. An inadequate generator or alternator or battery will still be inadequate whether a relay or not.
I have to conclude with Jack's concern for reliability. An original Healey has 3 components in its lighting circuit that might fail. The headlights themselves, the dimmer switch and the headlight switch. In the case of adding relays you now have 5. The headlights, the dimmer, the main headlight switch and the 2 relays. You can improve your headlight circuit reliability by 40% if you remove the relays.
 
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