H4 wiring harness upgrade

[NightKids]

I just tested the voltage from the headlight (with factory wiring) socket and I got 11.9V and 12.6V. Then i tested it with the engine on and both sockets came back with 14V. is this correct? The voltage seems too high for factory harness. Am I measuring it wrong?

[02gzm]

This was at idle yea? That's fine, your alternator should be charging at around 14.5V with no load

[NightKids]

11.8V or 12.6V are idle and 14V Is with car running. I thought the voltage was a bit high and the harness wouldn't make much difference.

[riruiz_88]

thats perfect man. the harness is able to handle it, cause it is tested from factory for an insulation breakdown of 30V (im quite sure). reason being is because as the alternator is spinning at a faster rate while running (not idle) it is able to to create a jump in voltage.

sorry if its not clear, its easiest i can explain it.

[NightKids]

Oh ok I was expecting lower voltage so then after I install the aftermarket relay, I can see the increase.

[riruiz_88]

the relay wouldnt really affect the voltage.

i must say that the kit is very different to what i would have imagined. i for one dont like the way the kit has to be to attached to the battery. would look much neater if the kit would go to the fuse box instead. but i do hope it is working out for you man.

[02gzm]

It's because they're pulling current directly from the battery now instead of running through metres of wiring. Your alternator supplies voltage at slightly above 12V to compensate for the 12V that the battery is supplying the rest of the car. This makes sure there is more power going in than coming out so the battery doesn't go flat.

If you wanna check your alternators condition while you're in fix-it mode, turn the high beams on, the fan on, rev the car to 2000rpm and check the voltage at the battery. If it's over 12.5V with all that load then you're car is handling it fine

[dahondr98]

I just tested the voltage from the headlight (with factory wiring) socket and I got 11.9V and 12.6V. Then i tested it with the engine on and both sockets came back with 14V. is this correct? The voltage seems too high for factory harness. Am I measuring it wrong?

Were the headlights on? If they weren't, you'll just get the battery voltage with the engine off, or the alternator voltage with the engine on. To test for voltage drop, you need to turn the headlights on, and then compare the difference between the voltage at the plug with that directly across the battery. There will be no voltage drop if the headlights aren't on, as they won't be drawing current.

[riruiz_88]

you can still get voltage even with the headlights off, should get battery voltage. but since he said he is getting 14V, the engine would be on.

[NightKids]

OK I popped the relay and overwattage bulbs in last night. I'm not sure if the relay really did much cause I couldn't even tell the difference. After I put in the overwattage bulbs and turned them on, I was quite dissapointed as well.

I was driving along the street with the street lights on & feeling pretty down that I wasted $100. Then I turned into a dark side street and that's when things got interesting. The light was so good! Everything was just so much clearer than before it was amazing! These 100/80 Osram bulbs are rated around 1700 lumens on low beams and it looked the goods. I compared it to a Corolla with Vision Plus (H7 bulb base) which should have been rated around 1500-1600 lumens and my lights were indeed brighter.

Can't wait to take this to the mountains or something in the rain. Pictures can be supplied if requested.

P.S. Tried to give you all rep points but doesn't seem to work here in the noob forum?

[dahondr98]

Glad you noticed some difference. It's sometimes hard to notice any difference in brightly lit areas, but you definitely should be able to get some benefit from the new loom, even with old globes. On a different note, halogen globes do gradually get duller over time, so it pays to replace them after a few years of use with new ones. No, I don't work for Philips or Osram, or anywhere that sells globes.

[NightKids]

Glad you noticed some difference. It's sometimes hard to notice any difference in brightly lit areas, but you definitely should be able to get some benefit from the new loom, even with old globes. On a different note, halogen globes do gradually get duller over time, so it pays to replace them after a few years of use with new ones. No, I don't work for Philips or Osram, or anywhere that sells globes.

Thanks you've been a great help. Your knowledge on harnesses and halogens is kinda freaky. I reckon I've got prob the best halogen bulb for the H4 (Osram Rallye) so don't know what I'll buy next. Prob the Philips NightGuide which looks kinda cool with the 3 colours. LOL