Headlight loom upgrade

Submitted: Thursday, Jun 17, 2010 at 21:15
ThreadID: 79435 Views:6904 Replies:2 FollowUps:10
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Howdy partners,

I am in a little dilemma and might need to enlist the help of someone in the know. I am rewiring my headlights with thicker wiring and dual relays and the rest. I have it all in the vehicle and set up, but i just cant get high beam to work, it just stays on low beam.

See i cant work out what wire i take as high and what one is low on the headlight plug. H4 plug by the way, vehicle is Mazda BT50.

When i test it i get,
No power when lights are off or on park lights.

2 outside plugs have power when low beam is on.

Middle plug and one outside wire has power when high beam is on.

Sorry but i dont understand it, is that negative or positive switched or is it a mixture of the two? It seems that the outside terminal that has power regardless is the low beam wire, and its earth is the middle wire, but when switched to high beam the other side of the plug becomes the high beam power and low beam becomes its earth?

Im a little lost, so i've probably just confused the hell out of you too. I just need to know what kind of positive/negative switched system it is and then which wires i would take to trigger the relay for them.

Thanks for any help that can be offered. I always thought it was positive switched so i could just run 2 trigger wires from the 2 outside terminals on the plug, but this isnt the case.

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Reply By: Member - Phil G (SA) - Thursday, Jun 17, 2010 at 21:25

Thursday, Jun 17, 2010 at 21:25
Is it worth rethinking this? What was the voltage drop in your wiring before you started?

Upgrading the headlight wiring was something we used to do on vehicles that were 15-20 years old and we wanted to fit high wattage globes. These days you can buy more efficient globes, and vehicle wiring is better. I measured the voltage drop on my last Prado and on my 2002 Landcruiser and in both cases figured there was no advantage to upgrading the wiring - just fitted the plus50 globes, or I have a mate who got a great improvement out of the ARB Fatboy globes.
AnswerID: 421249

Follow Up By: Muntoo - Friday, Jun 18, 2010 at 15:07

Friday, Jun 18, 2010 at 15:07
Yeah thought about that, but i wanna run bigger globes so will need bigger wiring. I think the voltage drop was .4v or something, which i was told was significant to a halogen globe which is designed to run at max temp.
FollowupID: 691647

Reply By: Ozhumvee - Friday, Jun 18, 2010 at 07:28

Friday, Jun 18, 2010 at 07:28
You don't say what the vehicle is, some have a weird way of wiring things.
If it is a Toyota then they switch both ground and power.
The easiest way to upgrade the loom is for the original wiring to activate the new one. Use one of the three pin headlight sockets to drive the new loom/relays.
You will also lose the dash indicator for high beam. Piranha, ARB etc sell upgrade harnesses.
Some vehicles like 80 series have plastic reflectors so fitting higher wattage lights will lead to reflector meltdown due to heat. So you need to fit aftermarket metal reflectors with glass lenses.
While they are technically illegal a set of correctly adjusted HID's will provide a huge increase in light and have a much lower current draw and the standard harness will be all that is necessary.
AnswerID: 421252

Follow Up By: Mark Howlett - Friday, Jun 18, 2010 at 10:03

Friday, Jun 18, 2010 at 10:03
He mentioned it was a BT50. As for the rest, I just drop in Plus50 globes with good (cheap) results and will do so with the Plus80 when they drop in price.

FollowupID: 691592

Follow Up By: Ozhumvee - Friday, Jun 18, 2010 at 10:45

Friday, Jun 18, 2010 at 10:45
Sorry missed the bit about the vehicle.
FollowupID: 691600

Follow Up By: Muntoo - Friday, Jun 18, 2010 at 15:05

Friday, Jun 18, 2010 at 15:05
Yeah Bt50, and i will be using the existing wiring as a trigger for the new relays. I had HIDs in my old Landcruiser and they were overkill. There is a reason why there illegal, too bloody bright.
FollowupID: 691646

Follow Up By: ben_gv3 - Friday, Jun 18, 2010 at 15:13

Friday, Jun 18, 2010 at 15:13
WRT to the +50/80/90 series of globes, be careful with them. To get the higher output they wind the wire tighter (I'm not sure if the wire diameter is smaller to compensate) and I think use a different gas, which makes them more fragile.

I used +50's but they died after a few years. I then tried Osram (or Phillips I think) +90's and they lasted about 3 months. I now use +30's as they are cheap.

I've also upgraded my headlight wiring just because I can (I have the tools and knowledge to do it myself).

Even Osram/Phillips tell you that the + globes don't last as long as their normal globes.
FollowupID: 691651

Follow Up By: Member - Phil G (SA) - Friday, Jun 18, 2010 at 15:35

Friday, Jun 18, 2010 at 15:35
Gday Ben,
The other factor is that increasing the voltage delivered to the globes will shorten their life.
FollowupID: 691655

Follow Up By: Muntoo - Friday, Jun 18, 2010 at 15:44

Friday, Jun 18, 2010 at 15:44
I read somewhere that increasing the voltage will increase their life. The more volts, the hotter they can get and the better it is for the globe.

But aside from that, my headlights are plastic jobbies, so i guess using larger wattage globes wouldnt be smart would it?
FollowupID: 691658

Follow Up By: ben_gv3 - Friday, Jun 18, 2010 at 15:48

Friday, Jun 18, 2010 at 15:48
Hi Phil,

Yes I have considered the increased voltage to be factor in the shortened life of the +90's, but I've read that lights like to have full voltage to function optimally.

My reasoning is also that I would rather get full voltage to the lights and then only using +30's as opposed to using OEM wiring (which is very thin BTW) and using +90's which may or may not stress the undersized wiring.

FWIW it wasn't much of a hassle to upgrade the wiring
FollowupID: 691660

Follow Up By: ben_gv3 - Friday, Jun 18, 2010 at 15:51

Friday, Jun 18, 2010 at 15:51

My headlights are plastic as well. Using +90 H4's is still using 55/60W so shouldn't get any hotter then OEM.

My headlights are H4's as well and I didn't have any problem with upgrading the wiring. I used 2 relays (hi/lo).
FollowupID: 691662

Follow Up By: Member - Phil G (SA) - Friday, Jun 18, 2010 at 16:50

Friday, Jun 18, 2010 at 16:50
Muntoo, I think you've been led astray regarding bulb life. I pulled the following from Wiki regarding halogen globes:
"The normal relationship regarding the lifetime is that it is proportional to voltage to the power of -14. For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the efficacy would be about 6.5% higher, but would be expected to have only half the rated life."
FollowupID: 691671

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