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  • 1 Post By patrickt
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Old 12-16-2018, 03:07 PM
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Default Headlight Wiring Upgrade

In another thread I wrote about measuring voltage drop, with the headlights on, across the left screw of the #1 fuse and the #7 and #8 fuses to see how efficient the under dash connections are. ERA cars have a Lucas toggle switch, a VW dimmer relay, and some connections under there. When I did that on my car the voltage drop was .7 volts, which is a little high. In a dark garage, if I jumpered across the same connections (thus bypassing all the under dash connections) the increase in light was noticeable, but not earth shattering -- but any increase in light is welcome. When I measured the amperage on the under dash circuit it came in at 13 amps, with about 2.8 amps of that going to the parking lights -- but all of that current passes through the Lucas toggle switch. The setup is probably just fine the way it is. But, with all of that current going through the Lucas dash switch, it would be helpful to know the rating of the switch itself. Now, the Lucas #31788 OFF-ON-ON switches have about five flavors of re-pops. The original OEM switch was only rated for 10 amps, but some of the aftermarket clones are supposedly rated at 15 amps and a couple even say 20 amps (but in the same literature they then also say 15 amps). The video put out by Holden-UK on Lucas toggle switches says they're all only rated for 10 amps, including the really nice ones that are licensed by Lucas and that cost more. So, I don't know what the rating of my switch is but, after looking at it all, it's so darn easy to do an upgrade that I just decided to change the headlight wiring to incorporate two SPST relays, with built-in fuses, that connect in tandem. I bought five of them off Amazon for about $15. ERA's wiring makes the upgrade about as easy as it gets. The skinny little BLUE/WHITE and BLUE/RED feeder wires to the headlights are readily visible from the engine compartment. Just cut them, run 12 AWG wires from each to the passenger side fender well, use the wires that originally ran to the headlights at either of the two cuts that you just made as trigger wires at the relays. Then run a nice fat 10 AWG wire from the #1 fuse connection around to the relays, add a ground, and mount them on the passenger side aluminum wall. Clean it all up so it looks nice and that's pretty much it. The lights are noticeably brighter and there is now only 3 amps going through the Lucas toggle switch -- surely it can handle three amps. Here's a pic of the dual relays. I had upgraded the bulbs years ago and the next time I take the headlights apart to clean the glass I'll upgrade the last little bit of wiring at the lights, which look to be pretty skinny. They're only about 18" long though. Other than the dual relays on the wall, you'd never spot the installation.

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Old 12-16-2018, 09:16 PM
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That's a no-brainer upgrade, Patrick, to have dual relays wired as a redundancy setup. We should all do that!

Cheers,
Glen
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Old 12-17-2018, 04:34 AM
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Well it's easy to tell whether you'd benefit or not. Just touch a jumper wire from fuse #1 to fuse #7 with the high beams on and if the lights get noticeably brighter then you do. And it really is easy. You'll have it roughed in and working in about 15 minutes, seriously. Done and cleaned up in less than an hour. Relays, wire, and butt crimp connectors will total less than $25. And you won't have to worry about that crappy Lucas toggle switch overheating either (although Bob's parts are generally pretty good). Here's a link to the relays off of Amazon. They're rated for 30 amps, I have a 20 amp fuse in each, and they're running at 10 amps. https://www.amazon.com/gp/product/B01NBAO1SA
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Old 12-17-2018, 07:09 AM
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That Amazon relay assembly is pretty slick (and cheap). It even includes integrated fuses. The only downside is you would normally get their power directly from the battery, and that doesn't show on the ammeter - but that is not necessarily a bad thing.
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Old 12-17-2018, 07:56 AM
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...doesn't show on the ammeter - but that is not necessarily a bad thing.
No, but would show up on a voltmeter.
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Old 12-17-2018, 08:41 AM
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Not having to screw around with the under-dash wiring makes this a pretty simple tweak. I've never been a fan of the traditional 60's "everything through the light switch" design that Detroit used on pretty much everything. I don't recall seeing any Lucas switch failures on this forum, but it's pretty common on some of the British car forums.
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Old 12-17-2018, 09:47 AM
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Quote:
Originally Posted by patrickt View Post
Not having to screw around with the under-dash wiring makes this a pretty simple tweak. I've never been a fan of the traditional 60's "everything through the light switch" design that Detroit used on pretty much everything. I don't recall seeing any Lucas switch failures on this forum, but it's pretty common on some of the British car forums.

Many years ago, when I was young and didn't know better, I installed a pair of fog lights and a switch to control them. It wasn't very long before the fog lights no longer worked and the culprit, of course, was the switch.



I learned then a switch is a good way to control a low current circuit or relay, but use relays whenever it's necessary to handle a higher current. That's not only more reliable, but safer as well.
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Old 12-17-2018, 11:08 AM
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Patrick,
Nice mod. That's a pretty big current draw. I'm leaning toward LED headlamps and tail/brake lights (I know not DOT rated yada yada) and tail lights. I'm guessing the lower current of the LEDs would eliminate the risk of too much current on the switch?
Evan
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Old 12-17-2018, 12:29 PM
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Patrick,
Nice mod. That's a pretty big current draw. I'm leaning toward LED headlamps and tail/brake lights (I know not DOT rated yada yada) and tail lights. I'm guessing the lower current of the LEDs would eliminate the risk of too much current on the switch?
Evan
Yes, LEDs draw less current. For instance this nice headlight Complex Reflector, 7" Round LED, 2 Diodes Headlight, Polycarbonate Lens, E-Coat Aluminum, 12-24V | Truck-Lite only draws 3 amps, which is roughly half of what we're used to seeing. Now I have the LED brake/tail lights, and the brake lights run on a different circuit than the Lucas toggle switch anyway. But my two LED tail lights in the back, and the two running lights in the front, all pull down 2.8 amps including whatever resistance happens to be on the circuit as well. So if you went with LED headlights, which will eat up about six amps, plus two and a half for the LED running/tail lights, you're still crowding ten amps for the circuit, but it's certainly less than normal headlights and tail lights. A decent switch can handle that current pretty easily, but anything that even looks like an authentic Lucas piece of equipment is suspect.
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Old 12-17-2018, 02:36 PM
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Yes, LEDs draw less current. For instance this nice headlight Complex Reflector, 7" Round LED, 2 Diodes Headlight, Polycarbonate Lens, E-Coat Aluminum, 12-24V | Truck-Lite only draws 3 amps, which is roughly half of what we're used to seeing. Now I have the LED brake/tail lights, and the brake lights run on a different circuit than the Lucas toggle switch anyway. But my two LED tail lights in the back, and the two running lights in the front, all pull down 2.8 amps including whatever resistance happens to be on the circuit as well. So if you went with LED headlights, which will eat up about six amps, plus two and a half for the LED running/tail lights, you're still crowding ten amps for the circuit, but it's certainly less than normal headlights and tail lights. A decent switch can handle that current pretty easily, but anything that even looks like an authentic Lucas piece of equipment is suspect.
Yes, that's it.

Any vehicle that hard wires headlight current from the battery to the cabin switch WITHOUT relays is asking for trouble.

One of mine eventually burnt the headlight switch, 30 mph at night, gave me time, thank god it was not a 60mph on an unlit road.

Gary
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Old 12-17-2018, 02:56 PM
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I had an Olds 442 back in the 70's that if you jiggled the light switch, because it pulled out towards you to turn on the lights, you could get the lights brighter or dimmer. I remember that at the time I thought that was kind of cool.
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Old 12-18-2018, 04:47 AM
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Quote:
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Yes, that's it.

Any vehicle that hard wires headlight current from the battery to the cabin switch WITHOUT relays is asking for trouble.
Gary
That would include most British cars built before 1970. Even VW didn't use a relay until about 1968.
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Old 12-18-2018, 05:23 PM
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Quote:
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That would include most British cars built before 1970. Even VW didn't use a relay until about 1968.
Yes, exactly.

How there weren't even more fires in the early days.

Gary
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Old 12-18-2018, 05:45 PM
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Electricity wasn't as hot in the 60's as it is today.
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