h4 Headlight Upgrade-- What relay do I need to get?

[VW Addict]

I am upgrading my H4 Headlights, to a higher wattage. Maybe something around 80, instead of 55. Can someone help and tell me what upgrade I need to get for a headlight relay? Thank you!

[Meiang]

More importantly what voltage are you getting at the bulb socket plug so that you will get the full output of the 80/80W bulb. I would recommend powering the bulbs directly off the battery and use the existing wiring setup as a switching circuit. Upgrade wiring looms are readily available for H4 systems.

Also you will not be putting any stress on an old wiring system.

[VW Addict]

Hmmm... OK, So another question...f I just get 60/55 H4's, can I use the same relay I have and wiring harness?

[Meiang]

I thought you wanted to upgrade the headlights. The factory wiring for 1968 models onwards was designed for 60/55W bulbs. Upgrading to 80/80W bulbs will make a huge difference if you can get the voltage to the bulb.

I would recommend PIAA H-89 bulbs as they were the best H4 performance bulbs made.

[Starbucket]

Buy a dual headlight relay at your local FLAPS (under $10). You use the existing car headlight wiring to the relay you mount under the hood and run a #8 or 10 wire from the pos. terminal of battery (put a inline fuse near battery incase the wire gets a short) to the relay, that way there is only a few amps through the car switches and relays and the bulbs get full power from battery. I ran 55-100 H-4 bulbs with this setup with no problems but a blinding glare to any driver coming at you with their high beams on when you blast them.

[Meiang]

A 55w low beam 100W high beam bulb does not give you any benefit over a standard 60/55W bulb at low beam which is where most people want the upgrade.

[bluebus86]

55 W /12 V = 4.6 amps

80 W / 12 : = 6.7 amps

Thus you will need a relay sized bigger than 6.7 amps.

the 2.5 mm sq wires used in the Bug is marginal for this current if the run is more than 10 feet, if you want to have low voltage drop.

See below chart link...

https://www.google.com/search?q=wire+capacity+char...QMB_JdZ2M:


Bug On, See The Light!
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[Meiang]

Automotive headlight bulbs are rated using a nominal 13.6v not 12v. An 80w bulb @ 13.6v should only be drawing 5.9A not 6.7A. Splitting hairs I know but the basis of calculation should be correct.

[bluebus86]

[74 Thing]

First check the voltage at your headlights with your current set up as suggested. Voltage drops here really effect light output. Fix whatever the problem is.

I added two Bosch relays (one for low beam and the other for high beam-the same Bosch relays sold for the hard start kits). Anyways bring a wire up from the battery with a fuseable link to the relays then connect them to switch on and off and replace your H4 bulbs.

There is a good selection on Rallylights.com

[Boble]

[bluebus86]

[Starbucket]

[Boble]

Bluebus86, thanks a lot for your very good description! Appreciated.

[ashman40]

First, start with the stock wiring. This diagram from Speedy Jim's site will show how the headlight switch, dimmer relay and fuse box are wired.

Notice that the dimmer relay controls the flow of current to either the high or low beams. The fuse box fuses only protect the part of the wiring that runs from the fuse box to the headlights.

Inspect all the old wiring you plan to use. After 30-40years the wire ends will oxidize and increase resistance; reducing the current flow that makes it to the headlights. If you are still using the original white and yellow wires to the headlights, consider snipping the ends off and re-terminating. Strip back the insulation until you get new clean copper. Or, replace all the old wires with new 12AWG wires as suggested below.

Combine this headlight relay circuit with the above.

Insert the pair of relays between the dimmer relay and the fuse box. Each new relay is powered by a separate 20A fuse from the battery (fuses located near the battery)... triggered by either the high or low beam output from the dimmer relay (white and yellow wires)... and each relay powers two fuses in the fuse box.

This arrangement reduces the current flow thru the headlight switch and dimmer relay; extending their lives. Use generic Bosch-style 20 or 30A SPDT relays you can get for as little as $3/each and they are easily replaced if they fail. Each individual headlight circuit is protected by an 8A fuse. If the circuit is shorted anywhere the 20A fuses near the battery will protect the long runs thru the chassis to the relays up front.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[bluebus86]

pictures worth a thousand words.

Bug On!
_________________
Help Prevent VW Engine Fires, see this link.....Engine safety wire information

Stop introducing dirt into your oil when adjusting valves ... https://www.thesamba.com/vw/forum/viewtopic.php?t=683022

[DurocShark]

And now I feel dumb for dropping H4's on my busses... both my 73 and my 78 had them. No relays or any of that. Worked fine and the light pattern from the Hella lenses was WAY better than from any sealed beam garbage.


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No boom today. Boom tomorrow. There's always a boom tomorrow.

[AlmostHeavenWV_VW]

Two above wiring diagrams combined (with the help of Ashman)

Complete wiring diagram for adding power relays to the headlight system

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1973 Standard Beetle
1600DP AK case
Solex 34PICT3 Carb
Bosch DVDA 205AJ Distributor

[heimlich]

Drop some LED's in there.
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[Dake]