Headlamp Relays vs. New Headlamp Wiring Harness

[SpacerM]

I’m interested in upgrading my headlamps to make them brighter, and perhaps move to halogens if I don’t get the illumination I’m looking for out of just upgrading to a relay. I run low/high beams only- no fog or driving lamps.

From reviewing the threads, there are three ways to I see to add the relay:

1. The “Moss Kit” method (https://www.mossmotors.com/graphics/products/PDF/117-515.pdf ) which involves routing the relays at the bullet connectors by the firewall but leaving the harness otherwise intact.
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2. The “healey 6” method (https://healey6.com/Technical/Let there be REAL Light.pdf ) that involves a completely new harness, including re-wiring of the toggle switch.​

3. The “New Harness” method which involves installing the relays, using existing wiring for the relay-to-switch connection, but running a new harness from the relays to the headlamps.​

I’m interested in keeping my car as close to stock as possible and try to avoid “replacing just because it is old”whenever it’s safe to do so.Therefore, the complete reversibility of the moss method has appeal; however I don’t want to jeopardize safety if the load for the new halogens will overpower the old harness run from the relays. It seems most of the halogens are 60W, so that’s a significant bump over the existing 40-50W draw the original harness was built for.

Will installing relays but using the existing wiring for the relay-to-lamp run present a safety risk?

 

[RAC68]

The conclusions you’ve drawn after reading “Let There beReal Light” are concerning and I am afraid I may not have done a good job inwriting the article. The approachpresented is a full do-it-yourself and not a kit so, if you are not up tobuilding your own, I would recommend following another path.

Good luck,
Ray (64BJ8P1)

 

[SpacerM]

Ray- thanks for the note. I apologize if my quick summary mis-characterized your article in any way- I have read it several times and appreciate the effort you put into it and believe I fully understand you points. I am fully capable of the wiring and soldering needed to implement the relays whether via kit or from scratch. My personal preference is that "time is money" so a pre-wired harness ( such as https://www.lmctruck.com/icatalog/cc/full.aspx?Page=72 ) seems like a good timesaver for $30. Also, again, purely personal preference, but my goal is to keep it as original as possible while still being reasonably safe (after all, all old cars present some heightened risks).

My only question to the group was whether relying on the original wiring harness to carry power from the relays to the two headlamps was an unwise choice and that I should install completely new wiring (aside from the trigger line) if I was contemplating relays.

Sorry again if I was unclear (either about my goals or your article) in any way.

 

[RAC68]

If retained, your primary electrical choke, and greatest fault risk, will be this wiring from the relays to the headlight plugs. You will be installing relays that are probably capable of delivering more than 20 amps to the lights and, although you will not be drawing all this power, the original gauge wiring is not sufficient to carry anywhere near that much amperage. I would strongly recommend that this wiring be replaced with lower gauge (higher capacity) wiring to allow your new Halogens deliver full lighting power.

Last, by changing the original source of power to the light switch from the ignition switch, you will reduce the risk of loosing both ignition and lighting from a single fault. The original lighting circuit has no fault protection (not fused) with all lighting power delivered through the switch. Switch power draw was further increased by many who had installed driving lights. Although you will be significantly diminishing switch power draw with the installation of your new relay setup, light activation will still be dependant upon this central unit. I considered it a good idea to separate lights from ignition to reduce this risk and to further protect my new lighting arrangement with the installation of in-line fuses from the relays to the headlights and/or a circuit-breaker covering the power feed to the relays.

Hope this helps,
Ray (64BJ8P1)

 

[Leo_Speichinger]

I installed the moss kit and installed a fused wire from the soleniod to the relays. It was a simple install. A 65W bulb only draws 5 amps so the Moss Kit's wire is plenty heavey if only running the headlights off them, as is the original harness wires. I also cleaned all the bullet connectors and applied NoOx to eleminate future corrosion at the bullet connects (a dirty connection is a high resistance area)

Leo

 

[GregW]

Last, by changing the original source of power to the light switch from the ignition switch, you will reduce the risk of loosing both ignition and lighting from a single fault.

Hi Ray,
I've seen you post correctly in the past, but the light switch gets its power from the regulator, not the ignition switch. The brown (or brown/blue) wire from the regulator to the light switch is pretty beefy. Probably wouldn't need to replace it as you mention in your PDF.

 

[RAC68]

Greg, you are absolutely correct, the power to the headlight switch does come from the regulator and I was both incorrect and incomplete in my explanation.

When converting my BJ8 to an alternator, I used the regulator as a power distribution point and, although stripping the regulator internals, the original large and small brown feeds remained in place. Inside the regulator, these 2 spades are hard-connected so, in effect, all components fed by these 2 lines (ignition switch, fuse block, and light switch) form a single circuit. As a result, a solid fault emanating from any unprotected component connected to this circuit can, and has, caused total electrical failure.

When installing my relays, I drew main power from the alternator through a circuit breaker. However, activation of the relays remained through the original path from light switch through dip switch which gained power from the brown wire connected to the regulator. As a result, loosing activation power meant no lights and was open to failure initiated from other components on the same circuits.

By separating light switch power from this central distribution point and pulling it, along with relay power, directly from the alternator (connected through a circuit breaker), you will have, “for the most part”, separated ignition from lighting (now including both the powering as well as the activation of the relays). Further, by also installing a circuit breaker on the feed to the regulator from the solenoid, additional protection and separation will have also been gained.

However, I said “for the most part” since a point of catastrophic power failure remains. Since the car’s main power line from battery, through starter solenoid, to alternator remains the car’s main power backbone, a solid fault along this path can still cause total power interruption. But, then again, this is a Healey and you must accept some risk.

It is true that all will work without these changes and even the wiring from the relays to the lights will work. But, as I see it, if you are installing relays to off load old wiring and components while providing power for updated lighting, why retain old wiring never designed to carry the amperage (with safety margin) needed to fully power these new components?

Again, thanks Greg for pointing out my error, I really appreciate the correction as I do not want to mislead.

All the best,
Ray (64BJ8P1)