wiring routing and front clearance lights

Picked up the ezwiring harness for my jeep last week and I am trying to decided on which route I should use to run the wires to the back of the jeep. Should I go inside the body along the edge and drop down right above the tailights and run the wires inside a wireloom or should I go thru the firewall and drop down inside the frame. I have enough wire to go either route but I keep thinking running the wiring inside the frame will cause the wires to go bad earlier from exposure to water and road derbis. Plus I have headers and will have to do extra work to keep the wires away from them when routing the wires to the frame. Inside the body I am thinking they will be in the way. What have you done?

Second, I am trying to decide if I should run the front clearance lights as marker lights or use them as turn signals when I wire the jeep. I don't want to add additional lights to the front so I am trying to decide what would be most benificial. Turn signals would make other drives much happier and would be a safer. Marker lights would be the factory setup. Again any thoughts on this?

This is for my 58 CJ6 with v6 and outside frame headers.

 

Jeep started running the wires inside the body for the '75 model year. The aft wiring goes along the underside of the body edge to above the left rear taillight, then goes down through the top of the fender well to serve the lights and fuel tank. Staying inside the body till you get to the rear seems to be a good idea, if your fuse panel is located under the dash (it is in a '75 or newer). You'll lack the metal tabs Jeep added to the body to keep the harness up in the edge of the body - you'd have to figure out something like that to run the wires inside.

You can convert the 1156 style sockets to 1157 type with two filaments. Then you'd have the modern running/signal combo that newer Jeeps have. I'm sure your harness would accommodate that.

 

Never thought about running the 1157 with dual elements but that is what I will do. For some reason I had it stuck in my head that I needed to run either running lights or signal lights. The wiring harness has both lines. Thanks.

My fuse panel is going to be mounted inside the body to the left of the steering column. I haven't mounted the fuse panel yet until I have everything layed out and am sure of the location of the hole I need to drill into the firewall for the engine compartment wires. I am leaning towards running the wires inside the body. Won't be hard to weld some tabs in place to hold the wiring in place.

 

If you wire the clearance light between the running light circuit and the turn signal circuit, it will serve both purposes.

When the running lights are off and the turn signal is on, the lamp will be "grounded" through the un-energized filaments in the running light circuit, so the clearance light will flash on when the turn signal flashes on.

When the running lights are on, the other side of the lamp will be "grounded" through the un-energized turn signal. If you then turn on the turn signal, both sides of the lamp will be "on", so the lamp will extinguish. The result will be that the clearance light will be on when the running lights are on, and flash off when the turn signal flashes on.

If you're using LED lamps, it gets more complicated.

If you're talking about putting 1157's in the clearance light, beware that one filament is much brighter than the other. I don't know if there are legality issues with having such a bright light on the side.

 

Don't think "too bright" is a problem. The later Jeeps use a 1157NA in the turn signals in this manner.

Also, if you want to try what CO64CJ5 suggests, double check that the turn signal circuit is grounded and not floating when not energized. If grounded, it will be ok, but I suspect that when "off" the turn signal circuit simply floats and is not grounded.

 

I thought the turn signal and running lights would be open when not in use. One side of the bulb is grounded to the frame and the other would be connected to both the turn signal swich and running light switch or essentually a parallel circuit. But when the switches are both in the closed position the turn signal wouldn't work because the electricity would follow the constant 12v power and not the flashing 12v. Am I correct or am I missing something.

 

Open is floating, ie no circuit. You can have hot (+12V), ground potential, or floating.

I think you're right - but I can't tell if what's I'm understanding from CO64CJ5 is what you're thinking ...

I believe what is being suggested by CO64CJ5 is to route the ground of the running lights through the turn signal switch. To do this, you would have to isolate the shell of the single filament bulb and run a wire from the bulb shell back to the turn signal switch. This will only work if the "off" position of the turn signals is grounded. Then when the turn signals flash, they switch between ground (running lights grounded and lit) and hot (12V connected to 12V, lamp is off because there's no circuit).

But I suspect the turn signal switch switches between floating and hot, not hot and ground.

 

I know the fuse panel on my 71' was under dash. Looking back at it now wish I would have mounted it in the engine compartment instead of the original location when I did my rewire.

 

That is correct. Floating and hot.

 

Ok now I understand by running the ground circuit of the running lights thru the turn signal switch to where the turn signal switch is in a normally closed position. When the turn signal is activated the ground is broken (open circuit) and the lights flash. So basically running the circuit in series where the light switch is the on/off switch for power and then thru the light bulb and back thru the turn signal (as a ground). Good idea.


Mounting the fuse panel in the engine compartment, wouldn't the fuse panel end up getting dirtier mounted in there? Convience wise it would be nice. I did think about mounting the fuse panel inside of a pelican box and running the wires out thru a hole in the back of the box but couldn't think of a easy way to seal the wires coming out. Plus if I add/change the wiring I would have more to deal with.

 

Not quite:
There is no ground in the side lights other than through one of the filaments in the combination Turn signal/ running light. There is no "breaking of ground" connections so to say. The current needed to illuminate the clearance light is minuscule. this acts as a restriction to the current passing through the circuit so the unlit filament doesn't have enough current to light up but passes enough current to light the clearance light. The filament is acting like a ground connection at this time. But if both the turnsignal and running lights are lit, there is no ground path and the clearance light remains off.

Here is a little animation that might explain it. At the end of the animation, there is a description of what happens when you do loose ground to the turn signal parking light.

 

That diagram represents a lot of effort - I hope you didn't make it just for this thread. It runs so fast on my computer that I can't read it though.

Here it is in static form:



Assume all the filaments have the same resistance.

You have to think about which filaments are in series and which are in parallel, and consider the voltage drop across all of them to understand the circuit.

If the PL and TS are both floating, no lights will light.

Let the PL circuit be hot and the TS circuit floating. So there's a 12V drop across PL filament: full brightness. Current also travels through the FM and to ground thought the TI and TS, making a 2/3-1/3 voltage divider. The TI and TS are in parallel so they are both running at 4V potential, 1/3 brightness. The FM is in series with the TI/TS, so it's running at 8V, 2/3 brightness.

If the PL circuit is floating and the TS circuit is hot, both the TS and TI have a full 12V drop across them: full brightness. The FM is connected in series to ground through the PL, so both of those are at 6V potential: half brightness.

If both the TS and PL are hot, the PL, TS and TI all are connected directly to ground, with 12V across them, and are lit with full brightness. The FM is connected between two 12V potentials, so there's no current flowing and it's dark.

If you break any of the grounds, you'll again have 4 different cases (2x2 combinations) of performance of the circuit.

I think this just repeats much of what's in John's diagram, which I had a hard time following (just looking at the circuit is much easier IMO).

 

John,
Very nice diagram! Way better computer talent than I have. If I am thinking correctly your diagram is wired using a duel element 1157 bulb correct?

Timgr,
Now that my curiosity is awakened. At which voltage level will the light bulb begin to light?

Lynn,
After some overnight thought and opinions from other people I am going to go with the wireloom inside the tub. Thanks for all your input.

 

Good question. I think you'd have to test some bulbs to find out for certain.

In my post, I assumed that a light bulb is a constant resistance - but it's not. They change resistance a lot when the filament gets hot, so typically you have a turn-on surge of current until the filament heats up, and then they stabilize at a much lower current. Unlike a plain resistor, they have a non-linear resistance with voltage.

I'd guess that the bulb brightness will be roughly proportional to the voltage across it - but the only way to know for certain is to test some bulbs.

 

Interesting discussion, but it's not so complicated. I didn't make this up -- this is the way side marker lights are wired on a lot of vehicles.

It works because the side marker is "grounding" through several parallel filaments. When it's "grounding" through the running light filaments, there are at least 4 running lights in parallel (one at each corner). When it's "grounding" through the turn signal filaments, there are at least 2 turn signal lights in parallel (front and back). Also, the turn signal filaments are brighter, which means they have a lower resistance. The side marker filament will incandesce well before the filaments in series with it.

 

I saw in a magazine where they installed the panel in a tupperware type item with a lid in the engine compartment. It sealed well and kept water and dirt out

 

You've got the right idea, but your reasoning about putting multiple parking lights or turn signal lights in parallel is faulty. The parallel circuits are all connected to the 12V source (the battery), which has effectively zero impedance (an ideal voltage source, where current does not affect voltage). It does not matter how many circuits you line up in parallel - one will not affect the other.

You're right about the brightness of the filament though ... for a given voltage, a bright filament will pass more current and thus must have a lower resistance. Thus the less-bright side marker light in series with the more-bright turn signal light will not each have an equal voltage drop. Additionally the filament resistance is non-linear with current (resistance depends on filament temperature in a bulb), and this affects the voltage drop across each too. But assigning equal resistance to each bulb is instructive as to how the circuit works.

Sorry if I'm splitting hairs here, but I think this is interesting, and it was fun to evaluate the circuit.

 

Except that the parallel filaments are not connected to the battery. On the bottom side, they're all connected to ground. On the top side, they're all connected to the battery through a switch. If the switch is closed, it's effectively connected to the battery, but as you noted earlier, if the switch is open it's not connected to anything.

If you then connect a filament (marker light) to this open top end and connect the other end of that filament to +12V, current will flow through the filament into the open top end of the parallel filaments, through those filaments, to ground.

So you have this new filament connected between the open-top-end running light circuit and the open-top-end turn signal circuit, if neither the running lights nor the turn signals are "on", both sides of this filament will be pulled to ground through the parallel filaments on each circuit. If you then close a switch on one of the circuits, that side is pulled up "hard" to +12V while the other side is still pulled to ground. If both switches are closed, both top ends are energized, so no current flows through the new filament.

The paralleled "cold" filaments have a much lower impedance than the hot filament, as you've noted. As a result, most of the voltage drops across the hot filament so there's not enough power (voltage * current) to heat up the cold filaments. Most (almost all) of the power is dissipated through the hot filament as heat and light.

See if this makes sense:



Obviously, the turn signal switch is more complex than shown here, but it does boil down to this.

I hope this isn't getting too close to hijacking -- I think it's a useful discussion.