What route for new headlight wire?

[SGB]

Time to upgrade lighting, and it has been made clear on this BB that I must run a new hot lead (with inline fuse no more than 18' from batt terminal I think) from the battery through the center tunnel, up to the front trunk, to the relay board I must make. The question is: What are the suggested entry/ exit points? I figure its gotta go in to the firewall near the shift linkage. Drill a hole or ? What about at the front? Drill another hole? What guage wire? Are you sleeving it in any additional insulation? Should I have additional individual fuses on each relay (I guess on the hot feed to the bulb), or just one near the battery? 30 amps? Hep me fellers!

[914GT]

It would be good to have a fusible link or fuse near the battery terminal, then smaller amp fuses before the relays to each headlight. Give me the max. current draw and length and I can give you a wire size. You're probably ok going with a #10, maybe #12, but the heavier the better to give you less voltage drop. Ideally you want the full 12v right across the filaments.

[Dave at Pelican Parts]

What power rating on the bulbs? Power == current X voltage, so two 100 watt bulbs (200W) on a car (nominally 12V) draw 200/12 = 16.667 amps, steady-state. They can probably suck double that when they first light up.

--DD

[pbanders]

Here's an alternative. IMO, the lead from the battery to the positive junction terminal that's on the side of the fuse box mounting tab (a brown phenolic thing with a terminal junction on it) is capable of carrying the current for most standard light upgrades (e.g., going from stock or std H4 55/60's up to 55/80's or 55/100's, or using 100W driving lights instead of the std 35W fogs). I would consider running 10 ga. on a new terminal attached to this junction, inline fused, as the source. A lot less pulling and it should have minimal voltage drop.

Note that I'm assuming that you're NOT running the main/highs through the ignition, as is done with the stock setup, and that you're using an appropriate relay instead. God only knows what those bozos were thinking when they designed it that way.

[Dave at Pelican Parts]

The 73+ cars do not have that junction terminal. I'm not sure if new wire is needed or not on the later ones... Depends on how much current you're pulling and how long the wire run is. (And I mean total current through that wire, not just the "extra" you put through because of the lights.)

--DD

[pbanders]

DD, do the later cars have some other junction point?

[SGB]

Well OK....

Here are the pertnant details-
I'm replacing the stock sealed beams with some cool units from brazil that I connected to on this board a few weeks ago- they take H4 bulbs (I'm goin hella "super-white" or something in 55/60w), have built in H3 driving lights (50 w) and a third socket for a phillips t4w marker light (i'm guessin 4 w). Guess I could run the math, but there are just a few standard sizes, so I'm thnking 10 gauge wire. Is a 30 A fuse right for the lead near the battery? 10 A for others? Brad- I confess that my headlight circuit wiring is unchanged from stock, on my '73, but part of my light improvement project is to provide a new positive source for those H4 bulbs. In order to prevent the potential problem with the ignition switch, don't you have to run a new 10 or 12 guage wire anyway? So, follow up questions:
-proper fuse rating?
-entry exit points to center tunnnel
-possible alternate locations/ approaces to meet the load I propose?

Thanks all!

[pbanders]

I have a similar setup, H4 55/60's, H3 50W driving lights. I used the stock wiring, even the crappy part that runs the H4's supply through the ignition switch. Works fine, I've been through it with my DMM and there's little drop from battery voltage. I agree that a dedicated wire for supply from the battery would be better, especially with a power relay for isolation, but the stock setup is also workable. As for fusing, I = P/V, so for a single wire supplying all of your lights, with brights on, you're talking about something like 26 amps for a system voltage of 13 V, so I'd use a 40 A fuse inline.

[Dave at Pelican Parts]

There is no single junction point for the later cars. Several of the fuses are linked together on the supply side, and that all comes through one single battery wire, but there are a couple of other battery wires that also go to the fuse box.

As for where to run a new wire, I would run it along the existing wiring harness. I was able to pull the rubber boot off of the firewall inside the engine bay, and poke a coat-hanger through there to the back of the boot, which is at the engine shelf. I taped some wires to it, then pulled them back through the boot. Then I used that same coat-hanger to thread the wires through the firewall holes (note the firewall is two panels near the bottom and the holes do not completely line up!!). You can use the access panel on top of the center tunnel to help you fish things through.

Pull a lot more wire than you think you need, as it is difficult to pull more after you start laying the wires down along the harness....

Then lay the new wires in alongside the main harness. The harness is held by bent metal tabs, which are easy to un-bend and then bend back again after you put the new wires in there.

--DD

[914GT]

-entry exit points to center tunnnel

Can you drill a hole near the existing harness entry point in the engine compartment? I have no engine in my car so hard for me to judge the usual accessibility to this area. If you can get a hole big enough for the wire and a grommet, run the wire into the tunnel alongside the stock wire harness. Then bring it through the front firewall somewhere under the dash above the tunnel or over to the left side where the harness exits behind the fuse panel. Another possibility is to put a hole through the rear firewall below the battery, then run it under the carpet alongside the inner rocker, then maybe through a hole in the forward wall near the heat duct. Probably a few ways to do it, all of them a pain in the butt.

[Dave at Pelican Parts]

I don't like the idea of putting any more holes in my 914 than I absolutely have to. I think running the new wires with the existing wiring harness is a much cleaner approach.

If you do drill, remember to paint the edges of the holes to keep Our Worst Enemy from forming.

--DD

[SGB]

I agree Dave, but I am confused. Where is the original "harness". There is the relay board behind driver in engine compartment, and fuse panal at drivers left knee. Neither of these is near the center tunnel. I guess the "harness" is just the biggest sheath of wires running from the relay board to the fuse panel. Izzat right? So, do you recommend tapping into the positive lead near the battery, or is there a big enough feed going over to the relay board to sister onto it there? You just sqeezed the wire between the grommet and existing "harness? Is that where the metal is double? The harness has to zig-zag a little to make it through these holes, or are these different?

[914GT]

You also have to be careful with that 30 year old rubber boot around the harness by trying to thread a new wire through it or around it. But if it's in good condition it's neater to route everything in the same bundle, just more work. Whichever way you do it, just make sure your wire is well protected so it's not rubbing against sharp edges. You might look for wire with PVC THWN 600V insulation for better abrasion resistance and gas/oil resistant. Some of the wire I've seen is poor quality, and the insulation melts easy.

[Tidybuoy]

I ran a dedicated, fused wire for my front trunk amplifier. I used monster cable wheich is about the size of battery cable & is bright red. When I eventually upgraded to the Hella H4's I tapped into this cable.

It was a pain to install but after a couple of hours, I had a very neat & stock looking job. I started from the fron of the car & drilled a hole on the front wall (infront of the gas tank). The wire passes thru the hole & then meets up with the regular wiring harness that's near the steering wheel. I was able to pass the wire thru the existing rubber grommet (tight squeeze) and then I followed the wiring harness all the way to the fire wall (I taped the new wire to the existing harness). once thru the fire wall, you can try & get the wire thru the rubber tubes but it's very tough. I eventually just ran the wire along the outside of the rubber tubes and then up to the battery.

[Dave at Pelican Parts]

Originally posted by SGB
I agree Dave, but I am confused. Where is the original "harness".

A "wiring harness" is simply a bundle of wires. They usually have some kind of sheath or something wrapped around them, but not always. The main wiring harness runs in a channel on the top of the center tunnel. That is what I was referring to.

So, do you recommend tapping into the positive lead near the battery, or is there a big enough feed going over to the relay board to sister onto it there? You just sqeezed the wire between the grommet and existing "harness? Is that where the metal is double? The harness has to zig-zag a little to make it through these holes, or are these different?

Yes, from the battery. Yes, I squeezed some extra wires in. Yes, the lower firewall is double. Yes, the harness has to zig-zag slightly to get through those holes.

--DD

[SGB]

Well, I've got these new headlights.....
Built in H3 foglamps, and cool little "bling-bling" 4 watt marker bulbs too.
The housing is bigger than the removed sealed beam. I've been wanting that Dremel tool... So, after I got 'em mounted, it turns out the HL doors won't close all the way. Yeah. Disassemble, dremel more. They fit now, but I haven't even pondered aim. I don't wanna think about that yet. Then I connect the first new relay to the wire between the HL motor and the HL motor relay. Surprise! It's hot. All the time. Hmmmmm. OK. Re-evaluate. Here is the right (?) wire. Surprise. (well, not really, no surprise to me) Its hot except when the HL is closed. Hey wait. I'll wire the bling lights between these two. Off when closed, on when open. Connect...connect...whirrr Hey! the HL motor is going! And now the bulb is caught! Expletive! OK. Power going through bling light back to relay? Study wiring diagram more. The new plan is to wire between the motor drive circuit (which cycles -, +, - each time HL doors open or close) and the side marker bulb +. At least last night this made sense. Now I'm not so certain. The more I think about it..... I don't think the HL motor circuit will do, because it is neg in both open and closed positions. I haven't powered any other line. The initiation of my wiring mods started at this HL motor power take-off. I expected + when up, which would close and allow + from foglight switch (if fog lights on) to the coil of another relay powering new fog lights with lead taken off new 10 gage to high beam (the H and L beam replacement is not the problem, I got new relays in for those too). I want the bling lights to stay off until HL doors are up and on whenever the doors are up. Right now the PL will come on without the HL doors up, so I guess my new plan won't work. I could run 'em parallel to the low beams, but I would lose 'em at high beam. Feel free to study the wiring diagram at PP (1973, part 1). I know it can be done, I am just all crossed up now. Anybody got any ideas?

[914GT]

SGB, I'm a little confused with what you've got and are trying to do so don't know how much help I can be. But when you said 'I could run 'em parallel to the low beams, but I would lose 'em at high beam' what you can do is use some diodes to steer the current to your bulb or relay coil. This will let either the high or low beam circuit power what it is you want but without affecting either one (as long as you're not drawing too much current of course). This is basically an 'OR' logic gate.

[SGB]

Your confused? Not 'smuch as me! Uh, sounds like you understand circiutry alot more than I. Yeah- I need an "or" switch. Is there such a thing? A relay that stays at the position it is set to after power is off? There is prob some correct name for this..... Seems like I've seen these kinda things.

[914GT]

Here's an 'OR' circuit using a couple of diodes.

Either will power the relay depending on wich side is hot. There will be a voltage drop across the diode (< 1V) but that shouldn't be a problem for a 12V coil. You can get 6A diodes from R.S. for a couple bucks, actually a 1A rated diode is plenty for a relay coil. If you were to power lights directly without a relay then use higher amp rated diodes or parallel them. A Schottky diode would be preferred as it has only about .5V drop so you get more voltage to the lights. The relay you're describing is called a 'latching' type relay.

[SGB]

Gotta show off my final HL upgrade results. Everyones help was instrumental in getting this done. There were several intervening activities that kept me off the road (shift bushings and rear brakes) that I discovered while the car was up getting wires run for HL and MP3 player. Here it is with markers (bling-bling, eh?), H4 low beams, then high beams plus built in H3 driving lights. Also set up so stalk activates original (bumper) fog lights when lights are off