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Old 07-01-2010, 08:00 AM
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Headlight conversion question.

Hello again, I'm back with another question for all you geniuses out there...

I have a 1978 Caddy Coupe DeVille and my headlights absolutely suck! The sealed beams are just not bright enough for my liking. (I'm used to driving newer cars without sealed beams) So I was wondering how well the conversion kits work for the 4x6 lights. The car has a separate high and low beam, so I would need 2 of the kits (4 lenses/bulbs total).

So my question is, do these kits just plug right in and work? I mean, in my experience, nothing is "plug and play" as it says. Would my current wiring/power be able to handle brighter bulbs?

Another thing is, when my brights are turned on, my low beams stay on as well, I don't see a problem with this as it stands, but would that put more strain on the system with brighter bulbs installed?

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Old 07-01-2010, 08:41 AM
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You first need to make sure you have the proper electrical requirements. By that I mean wire sized accordingly, and all grounds in place and in good condition. If any of those are not up to par you will be disappointed in the conversions. I would first upgrade your existing headlamp system with relays and heavier wire. You will see a dramatic improvement in brightness with that inexpensive modification. See this site for a description
Here is but one schematic.


Vince
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Old 07-01-2010, 08:57 AM
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That was definitely a cool read!

But wouldn't a 78 Caddy already have relays such as those installed from factory? I would think that a car that was at the top of the game in the day (as far as options and luxury goes) would have something similar installed already.
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Old 07-01-2010, 10:24 AM
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basically agreeing with Vince....

2010-1978=32 year old wiring harness's and parts and connections (corrosion)!!!!

with age and use ohm's resistance goes up "starving" the lamps for energy over the whole circuit/system...

energy "flow" on a DC neg system is from the batt neg to the device so it is critical that there is no resistance on the neg ground "supply" side of the circuit starving the lamp for energy...

"shade tree" mechanic quicky tests:

check to see that the lamp socket itself is not corroded and then hook up a #10 jumper from one of the lamp socket ground wires direct to the batt neg terminal and see if the jumper-ed lamp is brighter than the other lamp....
(much brighter!=clean the socket grounds connect's and make/add permanent grounds wire's to the batt neg for a "belt and suspenders" worth of energy supply to the lamps)
"hopefully!!!" that is the cure!!!

no improvement with just the ground jumper???

make a second jumper with #10 wire and a 15A fuse in series on the jumper...
"carefully" hot wire test just the lamp itself with the motor running hooking the second jumper to batt pos and with the ground jumper connected and compare to the opposite lamp....

if it is much brighter with the pos jumper,,,there is ohm's resistance "somewhere" in the positive side harnesses/switch/connectors/relay/etc causing voltage drop...
(if no improvement then the lamps do suck )

trying to make a long story short:

if the fault is not just corrosion in the firewall connect and/or lamp socket and/or ground,,,it can help everything electrical in the car operate better by making a new heavy duty "independent" lamps power supply circuit as Vince suggests...

that takes alt amps load demand off the (worn) original wiring harnesses to better supply everything from the ign to the power windows (so they can live longer)....

got time and patience and feel lucky?:
you can measure the alt output V versus the voltage drop/loss with a meter at each point in the lamps circuit to find the resistance sources and correct them,,,,
a healthy circuit from the alt to the device will have less than .2V total loss (alt reads say 14.2V at the stud,,,should be 14.0V at the lamp socket)

Last edited by red65mustang; 07-01-2010 at 10:31 AM.
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Old 07-01-2010, 01:02 PM
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And this is why I said "geniuses" in the original post!

A quick fix is my best bet at the moment, as my funds are, shall we say... Lacking at the moment.

Eventually, I would like to do the conversion. I'm sure the newer bulbs will give me a lot better range. However, all of this new info is just that, stuff I didn't know. But now I do, and I'm glad I asked before I spent the $100+ to upgrade the lights.

I'd still like to know if the conversion lights are just "plug and play", though. And if anyone can point me to a little more in depth walk-through on how to wire the relays, it would be appreciated. I'm good with learning new things, and following tutorials, but I am a total newbie when it comes to electrical wiring. (except for stereo's, amps and a few lighting setups... Yeah, I used to "rice" up my cars a bit in the past. lol)
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Old 07-01-2010, 01:15 PM
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Quote:
Originally Posted by Rodillac
That was definitely a cool read!

But wouldn't a 78 Caddy already have relays such as those installed from factory? I would think that a car that was at the top of the game in the day (as far as options and luxury goes) would have something similar installed already.
Nope. "...at the top of the game in the day..."

You don't remember the late 70s, do you? Probably NOT GM's finest hour.

First, contrary to advertising puffery, these cars were mechanically and electrically no different than their GM siblings. Second, the headlight circuit runs directly through the switch - no relay used.
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Old 07-01-2010, 01:38 PM
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The relay conversion can be accomplished for less than $50 if you shop around. Two 12 volt 30-40 amp relays and 20 feet of #10 wire will do it. The improvement in lighting even with the old bulbs will astound you.

Vince
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Old 07-01-2010, 03:21 PM
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It was not unusual for the low and high beams to be on together in the older cars.
Vince is 100% correct, you most likely have poor ground connections, a lot of the older cars used the core support to ground the front lights and the core support relied on a mechanical connection to the rest of the body. Those connections go bad over time and you loose brightness of the lights. A similar scenario is true of the hot feed for the lights, dimmer switch contacts start to fail, headlight switch contacts start to show some resistance. The relay setup and a good dedicated wired ground will make a huge difference.
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Old 07-02-2010, 09:15 AM
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the "economy budget" way to improve your lamps lumens output by 25%+ is switch over to the Sylvania Halogen sealed beams,,,,they only cost roughly $10 to maybe $20 each and are just swap in....

"BUT"

Halogens do burn/operate hotter (more watts) than standard lamps and must have a very good ground and power side circuit wiring to keep the wires cool...

there are other kinds of brighter bulbs that are not such a energy power hog per lumen but my quick look up only showed Halogens for a 78 caddy????....
.................................

once you understand the relay amp rating and purpose for a relay then the wiring pretty much explains itself...

every time you turn on and/or off a electrical switch there is a hot electrical arc which attacks/burns/corrodes the conductive metal contact surfaces...

even though each headlamp operates at only around 5 amps (ex: 60Watts Halogen/14Volts=4.2Amps x 2 lamps on high beams) the HUGE physical contacts surface area in a 30-40 amp rated relay could/can be turned on/off a million times (???) before the 8.4 amp arcing eats enough surface to cause resistance/voltage loss/more amps needed....

combined with #10 wire which is rated to handle 30-40 amps safely (=stay cool for no resistance/no voltage drop),,,,you have made a "overkill" capable circuit for the positive side of the circuit (fuse at the batt power connect point to protect the wires/#10 to the 30-40 amp relay lug/#10 from the second relay lug to the lamp lug)

right now your "huge power contacts" are the very worn/burned/corroded huge contacts inside the dash switch itself!!!!
(and the wires are likely #14? which are constantly hotter due to more amps thru the switch which degrades them)

there is a wire wound coil in the relay which only needs around <1 amp to "pull in" those huge power contacts in the relay (which are held apart by a small spring with the power off)

by connecting the dash switch lamp(s) output power wire(s) to the relay coil(s) input lug(s) and ground lug,,,the dash switch contacts never see another major arc from high amps (and free's up energy to supply the brakes lamps/turnsignals/whatever so they will/can be brighter and everything live longer)...
.....................

step #1 is do the "shade tree" tests,,,,determine if the problem is on the neg or positive side of the circuit....

very very common on old cars that more than half the "dim" problem is resistance on the ground "supply" side which can be cured with just a ground wire added..
(the same is true for any other high amps devices like the heater blower or wipers motor,,,often just adding a copper ground wire from the device wire ground lug to the batt neg will improve how they operate)

PS;
I haven't seen a old car in along time where the power origination source (alt/batt/cables) didn't need some TLC!!!

the starter motor pulls a gazzillion amps and stresses the hell out of the cables and connect points....

if they are not all clean/tight/perfect then power to everything suffers (due to resistance) when the car/motor is running...

edit:
wise to go buy a new dimmer switch,,,,they are plenty cheap and easy to install,,,,it's the most probable "dim" problem source on the positive wiring side of the circuit (due to worn contacts and/or spring)

Last edited by red65mustang; 07-02-2010 at 09:25 AM.
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Old 07-02-2010, 09:32 AM
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I checked the connections on the actual lamps themselves, and they were a bit corroded and dirty, a cleaned them up nice, but it made no difference. So that's one slim possibility down.

Where exactly would I run this ground wire from, Red65? I do a lot of night driving, and a temp fix would be awesome until I can get the relays put in.
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Old 07-02-2010, 09:43 AM
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Quote:
Originally Posted by Rodillac
I checked the connections on the actual lamps themselves, and they were a bit corroded and dirty, a cleaned them up nice, but it made no difference. So that's one slim possibility down.

Where exactly would I run this ground wire from, Red65? I do a lot of night driving, and a temp fix would be awesome until I can get the relays put in.
A good place to run the ground would be from where the battery ground is connected to where the current headlight ground is connected to see if it makes a difference.

If you have a meter, you can check for voltage from the headlight ground point to the negative battery terminal with the lights on. It should be 0 or very close to it. The most you should see if everything it ok is maybe .25 volts.

Another good test would be with the lights on, check the voltage across the battery then check the voltage across the headlight connector while still connected. Again you should have less than .25 volt difference.
If the difference is high, you need to find the source of the problem.

The relay setup is a great idea but if the problem is on the ground side you will still need to fix that as well.
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Old 07-02-2010, 11:07 AM
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I just checked the ground, and it looks as if someone had already tried to fix the problem, as the lights are grounded to a metal piece right above the drivers headlight with just bare wires bolted to the metal. I took the bolt out and the connection couldn't have been very good because they didn't bother to take the paint off around the bolt (I'm new to this, and even I know to do that. lol) so I did that.

I also left the wires disconnected to make sure they were for the lights, and the lights didn't work, so I know it's for the headlights. I think there may have been an improvement, but the sun is bright and shining today, so I can't really tell until tonight.

The guy at NAPA suggested I put the battery on a charger over night (at least 12 hours) to give it a full charge. I told him I had a dead battery the other day and had to get a jump, and he said that the alternator won't charge the battery to full power, it will just keep it at whatever power level it is at when the car is started. However, that doesn't make sense to me, if that were the case, wouldn't it be running on extremely low voltage all the time after I got a jump?
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Old 07-02-2010, 11:58 AM
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the socket is only 2 wires (terminals),,,one is plus coming from the firewall/lamp switch,,,the other ground/negative socket wire is connected with a terminal and screw to the steel body (usually at/near the corners of the rad support,,,might have both lamps sockets grounds wires terminals on one grounding screw?)

step #1 is carefully clean those ground connections/terminals on "both" sides of the car (driver and passenger side)!!!
lamps are plenty bright=problem solved....

the ground supply wires if needed/helps will be connected at the ground screws direct back to the batt neg post cable connect....
(first try to just somehow connect it securely at the batt neg post and just somehow secure it to the cleaned ground screw to see if it is going to help)
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Old 07-02-2010, 12:32 PM
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Alright. The bolt that has the ground wires currently attached has two ground wires on it, and if I take them off, none of the lights work. If they were grounded individually (such as drivers side lights all grounded together, and passenger all grounded together, but not passenger AND drivers all grounded together) would the drivers side still work if I disconnected the ground for the passenger side, or would the whole circuit be down? I would assume thats the case, it makes sense to me. I don't see any ground wires on the passenger side, so I would think they are all grounded together on that one bolt.

Next question is, would I replace the entire ground setup that is on the lights now? from the back of the bulbs on?

Sorry about all the stupid questions, just trying to make sure I have things correct before I dive into this and take the whole front end apart.
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Old 07-02-2010, 03:26 PM
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Quote:
Originally Posted by Rodillac
Alright. The bolt that has the ground wires currently attached has two ground wires on it, and if I take them off, none of the lights work. If they were grounded individually (such as drivers side lights all grounded together, and passenger all grounded together, but not passenger AND drivers all grounded together) would the drivers side still work if I disconnected the ground for the passenger side, or would the whole circuit be down? I would assume thats the case, it makes sense to me. I don't see any ground wires on the passenger side, so I would think they are all grounded together on that one bolt..
Probably the whole circuit would be down.


Quote:
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Next question is, would I replace the entire ground setup that is on the lights now? from the back of the bulbs on?..


That would be the best way to do it, just splice on new heavier wires as close to the back of the bulb socket as you can get.



Quote:
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Sorry about all the stupid questions, just trying to make sure I have things correct before I dive into this and take the whole front end apart.
So I take it your going to with relays on your headlamps? Just come back if you have any more questions.

Vince
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