So I got into a not heated but kind of warm conversation about using headlight relays. I have all brand new wiring and headlight switch and dimmer switch. Nothing gets hot and everything works fine with my headlights (stock replacements) for my 69 Dodge. They light up the road fine at night and never dim. I don't feel the need to cut a brand new harness to add relays due to "fear", which in my opinion are a band aid for a bad electrical system. If I had high wattage lights well maybe it could be a good idea but reminds me of when Angelina Jolie wanted to have her boobs removed due to "fear" of breast cancer lol What do you guys think??? Thanks, Mike.
This issue is post HAMB, but could apply generally to anything. In your particular case, these era cars have a history of a couple of electrical issues where the OE design wasn't able to hold up over time. The first is the amp gauge circuit going thru the bulkhead 2 times. The second is the headlights, which also had long runs and many connectors which would deteriorate over time. It is surgery (not a band aid) for a bad design. It passed review, but failed in the real world over time. If you still have this era of cars in the local wrecker's, look at the bulkhead connectors on them. You will see heat damage. I've already mentioned which circuits will be the affected ones. If you replaced it all with as good as or better, this will be a situation where it will probably not fail for a long time. They withstood daily driver use (parked outside, driven in winter) for many years, so light duty fun car use (driven lots less, kept inside) will extend the time it takes for the design issues to show up. With some knowledge of the weakness, you could even keep an eye on this area and do preventative maintenance. However, the issues are known and proven mods are also known. I won't argue about it, it's your car. If it's a reference restoration, mods are not reasonable.
I think history shows that headlamp wiring doesn't require a relay. For how many decades did automobile manufacturers go without a relay, and cars never had failures until they had many decades behind them? Of course over time connections get corroded, and wiring or insulation breaks down, but it wasn't until modern cars began using high wattage lamps that the auto makers switched to relays. If your old car has a completely new wiring system with good grounds, and proper connections I see no reason to need a headlight relay myself. I own three old vehicles I've installed completely new wiring harnesses into, and none of those harnesses came with relays, and I didn't add any to them. I'm not the least bit concerned that they wont hold up even better than the old wiring that came out that was over 80 years old when I rewired them.
Part of the joy of driving an old car is having just enough light to see at night. but with modern cars having such bright lights, and us getting old and losing visual acuity, I guess it's not surprising that some folks will do whatever they can to try to get more light. Relays could help, as could different bulbs. But I still use "direct" wiring, and can see OK. Although my old cars have 4 headlights, which helps when you can use the high beams.
A lot of 30's cars used headlight relays when they were converted from bulbs to sealed beams. I suspect the sealed beams used mor power than the original switches could handle. That is one of the reasons for using a relay, so the switch can work with less power. A lot of late model cars use them for the same reason. You seldom see headlight relays on 60's cars. I guess switches were cheaper than relays in those days.
Think of a relay as a switch that can handle a larger load, that is controlled by a smaller switch. If you are turning on a device that has a high amperage draw such as halogen headlights or a heat- AC system a relay can handle the load that a switch can't. If the on/off switch you are using is rated for the existing lighting systems amperage, you probably don't need a relay. If your factory lighting system does not have an existing relay, why install one? I'm sure the electrical engineers at Dodge did their homework.
I use relays in my headlight wiring because I don’t trust the quality of replacement headlight switches, and I want to keep the under dash wiring loads as light as possible. Years ago I experienced a dash wiring fire with my father’s 56 ford big window pickup. Memories of sparks and smoke , and the smell remain vivid.
The thing with the conversation I was having with the other person about relays was the stock headlight switch has an internal circuit breaker in it, which we all know. If you have an overload problem the breaker will trip and the lights will go out for a second or 2/3 seconds, then on again and you can get to the side of the road safely or at least get home. With a relay if they go out, they are out period. If the connections are corroded and in bad shape, wires have issues, bad grounds, old wires, old switch, melted plug from neglect, other things tapped into the circuit there will be spikes in amperage and why I feel that relays are a band aid for bad electrical systems. He said relays don't go out ever, I said BS because if they get wet or humidity gets to the contacts they will burn out and leave you with no light at all. Seems like a 50/50 to me as far as relay or not lol But, like I said I have stock replacement bulbs, all new wiring, new switches and have no hot anything anywhere and no dimming, no breaker tripping and people flash their hi beams at me if I forget to dim mine. I'm leaving it the way it was designed but just wanted other opinions. BIG thank you to all you guys!!!
Circuit breakers don’t always trip, fuses are more reliable. Brighter than stock headlights are better than stock. On my kids OT Jeep XJ I ran a plug&play relay kit, no surgery required. With all that being said, I still like driving at night with just enough light to see. I can hit the high beams whenever I need.
There are multiple reasons as to why relays became a 'thing', primarily because of inadequacy in the aftermarket harness kits sold to us. But that's another story... However, headlights present a few unique issues. Pretty much all US-built vehicles from the '50s through at least the '80s used a headlight switch with a built-in 15 amp (more or less) circuit breaker protecting the headlight wiring. The 6V cars used a 40 watt high beam, so amp load was about 13 amps. That's pushing the limit on that breaker. When the conversion to 12V arrived, wattage was bumped up to 55 watts on high for a load a bit over 9 amps, reducing load. If you use a 'modern' road-legal 55/60 watt 7" halogen headlamp, max load only goes up to 10 amps, still well within the breaker's capacity. However, if you step up to an 'off road' lamp with a much higher high beam wattage, you will need a relay for high beam to protect the switch. Quad light cars do present some issues. When Detroit adopted 5.25" quad lights in '58, they retained the 50 watt low beam rating but lowered the high beams to only 35 watts. The improvement in lighting performance was due to better optics in the now-dedicated high beam lamp; the compromises needed for low beam were gone. Total high beam load was now 11.6 amps, still well within the breaker capacity. As long as you stick with OEM-wattage lamps, no problems. But if you decide to step up to a full set of modern halogen 55/60 watt low/high and 60 watt highs, high beam current will to go to 20 amps, exceeding the breaker's capacity. I prefer to relay only the dedicated high beams, the low/high lamps still going through the switch. You only need one relay that way, and in the event of a relay failure you don't lose all of your lights. FWIW, the best headlights I ever had were on a four-light car with 'legal' 60 watt high beams. A full set of Cibie lens assemblies carefully adjusted, they would light road signs out to nearly a mile. A premium reflector/lens design makes a very large difference.
After the second time explaining to a cop why I was flashing my headlights, I put one in my OT 96 XJ. The headlight switch breaker, no matter how many times that I replaced it, even with an OEM one, would overheat and trip with off-the-shelf DOT approved Sylvania Silver Star headlamps. I prefer to drive at night with all the light that I am legally allowed. Having access to simple and easy to use safety equipment, and refusing to use it seems like a bad idea to me. I can assure everyone who has not experienced it that having your headlights turn off, on a cloudy night, on a freeway in the middle-of-nowhere where there are no lights, at 75mph, is a less than reassuring experience. Relays are exceedingly inexpensive, and are a proven solution. Why anyone would resist using them is quite beyond my comprehension.
I don't know if all Mopars from that era were like this but at least one I worked on didn't use a relay so the knob-type lightswitch in the dash had too much power through the contacts causing arching and early death of the switch(s). Fellow I knew was replacing switches about every 18 & 1/2 months because he drove at night once in a while.
50s/60s OEM switches usually work pretty well....at least, those from some OEMs. Mopars...Fords...Jeep....not so much If it's broke, fix it. If it ain't broke, you might think twice before fixing it, because you might make it worse.
If I'm building the wiring from scratch, I like to use switches to control relays, where practical. Sized properly for the current draw of the item they're controlling, relays are able to handle higher current loads and less voltage drop than a typical switch. Proper layout of the relay/s will enable keeping positive wiring confined to central areas, instead of running back and forth through the body and frame, using less wire and safer. Most times, relays can be controlled/switched using the negative side of the holding coil, eliminating more positive wires running back and forth and over.
Just went out and scavenged some wiring from one of the vans out back the other day. Factory equipped quad rectangular headlights. You should be able to guess what decade. The one circuit I found that had got hot was the ground circuit for the headlights. We can guess how it was used/abused during it's life, who's to blame, and even explain how a relay wouldn't fix this. I will say the engineers may know better, but the bean counters may not. I understand the KISS principle of direct wiring, least number of connectors and properly sized switches. I also know that many here moan about component quality not being up to expectations. I'd say it's a 50/50 with each side having good points. I will say I do not like the modern driver input being a request to some controller. Give me a switch that makes and breaks a circuit (demand, not request).
As I recall, installing relays in the headlight circuits was commonly done in the '70s and '80s when higher wattage Halogen headlights were installed in the car.
In my OT truck(71 GMC) I got tired of replacing the foot operated dimmer switch every few months because it had burned out. I run 55/100 H-4 halogens in it because of the roads around here and when I was working I was either going to work in the dark or coming home in the dark and we have a lot of walkarounds that walk down the shoulder and some times middle of the road at night in totally dark clothes and often as not are impaired by alcohol or drugs. One got hit and killed by a hit and run driver 200 ft from my driveway. He wasn't found for several weeks. That is the main reason I run lights that work. Funny thing is that I ran the same lights in my 48 for years in Cibie bulbs and never had a switch problem. Possibly 20 years difference made a huge difference in the quality of the switches. For me running lights that I can see with and see the walkarounds with is important and the relays protect the system. If you don't have bulbs that put a higher load on the switches you don't have a problem from the start.
Two reasons (with a new harness), higher wattage headlights and/or NOS/NORS switches. With an old harness there are more reasons. I have them in 2 vehicles, because I like to see at night.
Just my opinion, but I think relays became so common in modern cars because they can be run through switches that are cheaper, and use much smaller wiring to control the relays. The relays and wiring are much cheaper than larger 12awg wiring and heavy switches that used to be common in cars without a relay. If your wiring and switches are all new, and sized the same as direct wired headlamps used to be, then there's no savings or improvement by adding a relay to the system.
And you can do the math and figure out what the voltage drop will be, for different lengths of different sizes of wire, and different currents. It can be significant. But the addition of relays will only "fix" part of this problem.
Think of relays as HP for electrics, more power at the light more HP (light) if your 12 volt system has 10-11 volts at the bulb supercharge it with a relay switching all the available to the bulb. Just dyno (measure) the HP(voltage) at the bulb and you’ll know what’s up.
In heavy trucks, the headlights are on relays and type I circuit breakers. They are also split from side to side. That way if you lose one circuit, you still have the other headlamp. Newer heavy trucks have multiplexed circuits but the headlights are mostly controlled by relays. However, some trucks use feild effect transistors in place of the relays.
I had an OT older mercedes that had a fuse for each of the four headlights. The fuse for the driver side low beam would always burn out after a while. Great system...sort of....I ended up driving with high beams on most of the time!
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