72T Headlight Wiring

The Dude · 12-28-2023, 04:18 PM

Doing some cleanup after a major body/paint restoration job.

Upgrading the fuse box (w/built in headlight relay) and headlights (H4 conversion kit).

Current status: headlights work but are typically dim (thus the conversion). The hi-lo beam switch on the stalk seems to work backwards. Push it away and it fires the lo-beams BUT the little blue hi-beam indicator/light on the tach comes on. Pull it towards me and the high beams are on. Maybe the hi-beam indicator goes out but it's really hard to tell cause it's really dim too.

In my prep, I pulled the driver side headlight off to see what I had to work with.

Mostly white/splotchy wire on top prong. Yellow/splotchy on left (outboard driver) side. Brown/ground on right (inboard/driver) side. (I have other pics but didn't want to overload this post.)

I came across this diagram of an H4 pigtail. Note the "standard" at the top.

Here's my current (pre-upgraded) fuse box wiring. Those top ones are fuses 1-4 on the "bottom-8" fuse box. Left is aft; right is fwd.

Looking at the official 72 Wiring Diagram (not pasted here -- too large):

Going down the right/switched side, I'm a match (White at 1/2; Yellow at 3/4). Going down the left/loaded side, it's mostly a match (White and White w/Blue at 1 vice mine which has the White and White w/Blue at 2). Yes, I know I need to get the right fuses in there -- later though.

So, if fuse locations 1 and 2 are for the hi-beam (White and White w/Blue)...and if fuse locations 3 and 4 are for the lo-beam (Yellow)...then I should have a Yellow wire on the top prong in the std H4 wiring scheme. Does this sound correct? Obviously I have something amiss OR the std H4 wiring is non-std on these old cars.

Anyone know the answer to how the H4 bulbs should be wired? Do I have an mis-wired stalk switch or are the wires simply in the wrong prongs at the back of the lamp?

P.s. Auto electronics are not my specialty.

PeteKz · PeteKz's Garage

Per my 1973 wiring diagram, and my actual car, the white wires are the high beams, and the yellow are the low beams. The fact that the blue high beam indicator comes on when you push the light stalk away indicates that the switch is wired correctly. I noted that you do not have the plastic plug that holds those spade connectors. It looks like the PO removed them. Maybe they melted due to high resistance connections. It happens.

I would do 2 things:
1. connect the wires to an actual headlight and arrange them so that the high beam comes on when you push the stalk, and goes off when you pull it towards you. Make sure you get the ground wire in the correct place first, or you will light both the high beam and low beam and they will be dimmer than they should be.
2. Get those plastic plugs and install the spades in the correct orientation based on your headlight test.

ed mayo · 12-28-2023, 06:01 PM

Order of wires on plug from the left is white yellow b r own.

The Dude · 12-28-2023, 09:53 PM

Quote:

Originally Posted by PeteKz

I noted that you do not have the plastic plug that holds those spade connectors. It looks like the PO removed them. Maybe they melted due to high resistance connections. It happens.

2. Get those plastic plugs and install the spades in the correct orientation based on your headlight test.

What plugs? Do you have a picture?

The Dude · 12-28-2023, 10:08 PM

Quote:

Originally Posted by ed mayo

Order of wires on plug from the left is white yellow b r own.

Right. Thanks. But do I start from the left side and go clockwise or vice versa? Looking at the back of the bulb?

https://forums.pelicanparts.com/porsche-911-technical-forum/827485-headlight-wiring-h4s-pics.html

Post #2 e.g.

I have found some further info saying the order should be ground/low/high (proceeding cw) when looking at the back of the bulb. See another post below (#10) below. Can't swear to its accuracy but its from Pelican so likely correct.

If so, then all my wires are wrong [yellow/white/brown] and ground should be the outboard connection on the driver's side.

https://forums.pelicanparts.com/porsche-911-technical-forum/156303-im-upgrading-euro-h4-s-yippie.html

PeteKz · PeteKz's Garage

Our sponsor sells them:
https://www.pelicanparts.com/More_Info/91163110800.htm?pn=911-631-108-00-OEM&bc=c&SVSVSI=4247

The Dude · 12-29-2023, 04:59 AM

^^^^^^
Thank you!

donporfi · 12-29-2023, 11:51 AM

The connections should look like this.

donporfi · 12-29-2023, 12:06 PM

The connections in your case should be changed to

The Dude · 12-29-2023, 03:21 PM

Yep. That's what it's looking like.

Same on the pax side too? The brown/ground wire on the left (inboard) post?

New problem -- slowly decreasing voltage at the hi-beam link.

donporfi · 12-29-2023, 04:35 PM

Both sides should be the same.
Left post brown, middle post yellow, right post white.

The Dude · 12-29-2023, 07:28 PM

yep. that's it. thx.

E Sully · E Sully's Garage

Make sure your lighting ground by the battery box is clean.

The Dude · 02:19 PM

Ed,
To what lighting ground do you refer? The normal ground for the driver side battery (-)?

The Dude · 12-31-2023, 02:19 PM

Break-Break

New question/direction -- how does everyone drop in higher gauge wires downstream from the headlight relays? Do you tear into the existing wire harness and replace the old ones or something else?

HarryD · 12-31-2023, 02:40 PM

Quote:

Originally Posted by The Dude

Break-Break

New question/direction -- how does everyone drop in higher gauge wires downstream from the headlight relays? Do you tear into the existing wire harness and replace the old ones or something else?

You can use the existing wiring for standard wattage bulbs (55 or 65) but it is prudent to go larger if you might ever want more wattage.

The two high beams will draw 130 watts (11 amps), the two low beams 110 watts (9 amps). If you go with 100 watt bulbs, total power is 200 watts (16 amps).

As far as wire sizing (https://www.stateelectric.com/resources/allowable-ampacities-of-conductors for capacity of various wire sizes and THHN type:

10 gauge - 480 watt (40 amps) capacity
12 gauge - 360 watt (30 amps) capacity
14 gauge - 300 watt (25 amps) capacity
16 gauge - 216 watt (18 amps) capacity

Wire size should always be at least expected demand plus 10% for safety. You fuses should NEVER exceed the ampacity of the wires.

The Dude · 12-31-2023, 04:04 PM

Thanks Harry. Seen plenty of your inputs on this topic over the years and appreciate your response.

I'm trying to figure out how people are running their new 14ga wire to the headlight. I really don't want to dissect my harnesses but can't see a way into the headlight bucket without going through those 6-point connectors.

Happy New Year to you.

HarryD · 12-31-2023, 04:18 PM

Quote:

Originally Posted by The Dude

Thanks Harry. Seen plenty of your inputs on this topic over the years and appreciate your response.

I'm trying to figure out how people are running their new 14ga wire to the headlight. I really don't want to dissect my harnesses but can't see a way into the headlight bucket without going through those 6-point connectors.

Happy New Year to you.

Best of 2024 to you as well.

I drilled a new hole and ran the wire through it with a grommet to protect the wires and seal the opening

E Sully · E Sully's Garage

Check out this video. 5 minutes in.
https://youtu.be/UK9dGyL9oEU?si=GKVfEXPEKCGtJP--

The Dude · 01:41 PM

That video just told me I needed a 4-post lift. Ha.

Seriously, that guy's editing is really well done. Good video. Thx.

I don't think I have a ground problem. Getting a solid 11+ volts at the lo-beam wire both sides (engine off). I think it's a problem with the hi-beam power at the fuse box. Once I get my new fuse box in, I should know more. It has those relays built in.