Understanding the running light switch

[jonathan-m]

I've been battling rear light issues for years now. I'm off this week, so I'm determined to kick them in the butt once and for all. I've run 10 gauge wire from the tail light housing to a grounding point on the frame, which itself is connected via a 10 gauge wire to a grounding point on the on the frame in the engine bay that is then ground with a zero gauge wire to the engine block ground. (Thanks to Markeb01 for the grounding idea)

I messed around with it a lot today and got the brake lights working and signals working properly. I replaced the flasher and I bought a new rear harness as well, which I will install tomorrow.
The one thing that I still have not gotten worked out is the running lights. As soon as I pull the headlight/running light switch the headlights function but nothing happens with the tail lights. If I hit the brakes with the switch pulled the brake lights function as normal, as do the turn signals.
I haven't been able to isolate what would cause this, so I was hoping someone would be able to point me in the right direction.

Thanks guys!

Jon

[jonathan-m]

Okay, I'm testing the switch right now, but the one diagram describing these wires here in the faq is for GMC and does not seem to match Chevy trucks. I know obviously the red is power, the brown I believe should be the one to the tail lights, and the light blue I believe runs to the dimmer switch for the front headlights (its the only one with power when the knob is pulled fully out, and the headlights are the only lights that work, so makes sense) .

Here's how it read when I tested each line:

Red- continuous power
White- none
Light blue- Power when knob pulled all the way out
Drk green- none
Brown- none
purple-Power when knob pulled half-way out
orange- None
orange2- none

Lines with none had no power in any knob position.
visually, none of the dash/guage lights come on, the dome light will work, but the fuse for it will blow after a few seconds of use. headlights work, running lights do not.

I completely dissembled the running light switch and cleaned it out, polishing all the interior contacts (they didn't look that corroded actually).

Anyone care to help me figure this out?

[jonathan-m]

okay, I found another diagram in the FAQ that seems to be a direct match for the chevy instrument panel. I color coded all the wires relevant to the light switch.



again here's how it read when I tested each line:

Red- continuous power
White- none
Light blue- Power when knob pulled all the way out
Drk green- none
Brown- none
purple-Power when knob pulled half-way out
orange- None
orange2- none

Lines with none had no power in any knob position.

[jimmyboi082]

are you checking for power with the switch bolted up to the dash? on mine the switch housing grounds itself when bolted up.

[jonathan-m]

hmmm I thought the white and purple neutral lines would be the grounds for the switch, not the housing itself?

[jimmyboi082]

I don't think none of those wires are grounds they all get power threw the switch depending on the position sending it to different circuits.

[protrash64]

This may be stupid, but you didnt mention it. Do you have 1157's installed in the taillites? They have two filaments.

Also, this whole problem could be in the turn signal switch.

[jonathan-m]

Originally Posted by protrash64

This may be stupid, but you didnt mention it. Do you have 1157's installed in the taillites? They have two filaments.

Also, this whole problem could be in the turn signal switch.

Yep, definitely the two filament bulbs. The turn signal could be faulty even if the turn signals themselves are working properly?

[Blue Heeler]

turn signal switch...solved my problem. it was worth the 40 bucks!! drove me nuts.

[fleetsidelarry]

Jonathan-m, one trick I use is a short jumper wire to supply power to each curcuit I want to test. Often this doesn't have to be anything fancier than a short piece of wire with the ends stripped (although a better way is to use an in-line fuse holder).

the brown wire for the tail lights should have nothing to do with turn signal curcuit and they should come on as soon as the knob is pulled one notch out, and should stay on when you pull to the headlight -on position.

try this quick test, unplug the light switch and jump between the red and the brown. this by-passes the switch and tells you if you have broken wire (not at uncommon) in the tail light curcuit, or a bad connection at the firewall plug (also, not uncommon)

I thinkthat my switch works out of the dash. the only light that this switch operates that isn't self-grounded may be the dome light, and it could be that the green wire that runs to the fuse panel is the ground for that lamp, but I don't know that for sure

it bothers me that your dome light blows a fuse, you may have wiring issues further into the harness, but do the simple jumper test first to eliminate the HL switch.

[jonathan-m]

Thanks Larry, I'll try that right now and see what happens.

[jonathan-m]

okay, the running lights do work when I run a jumper from the power to the brown wire. So that confirms there are no issues in the wiring beyond the headlight switch.

For some reason I have lost power to the orange wire that supplies power to the stop light switch, so stop lights do not work now.

What I did notice is that if I reinstall the headlight switch, and then run a jumper from the red(power) to the brown(running lights) the orange(stop light) gets power again if I pull the headlight switch knob either half way or all the way out (since the brown and orange wires are both activated by the switch in the half or full position).

I completely dissembled the headlamp switch again, and like I said everything inside of it is well cleaned and in working order. I could replace it, but there isn't anything out of order about it. I just don't understand why the brown( running light) wire does not activate when the switch is pulled, unless it is a grounding issue with the switch or somewhere else in that circuit.

[jimmyboi082]

When my running lights didn't work on the rear I had a bad turn signal switch. The running lights in the front didn't come on because they weren't required for those years so I relocated the wires on the switch to make them come on when the headlights come on.
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[jonathan-m]

Originally Posted by Blue Heeler

turn signal switch...solved my problem. it was worth the 40 bucks!! drove me nuts.

Originally Posted by jimmyboi082

When my running lights didn't work on the rear I had a bad turn signal switch. The running lights in the front didn't come on because they weren't required for those years so I relocated the wires on the switch to make them come on when the headlights come on.
Posted via Mobile Device

I've been staring at this diagram though, and I'm not sure how the turn signal switch could be the problem in this case since the turn signals themselves are working properly.

looking at this, it shows that the brown running from the headlight switch supplies power to the tail light harness, just as the orange supplies the power to the stoplight switch, which makes since as both orange and brown terminals are powered simultaneously inside the headlight switch when the knob is pulled out.

[fleetsidelarry]

Jon, I'm still confused too and thinking about it.

But, I will say that the orange wire to the brake switch SHOULD be hot all the time, regardless of the switch position. Brake lights are supposed to work regardless of the switch position. in the case of the brake light switch, the orange wire is simply using the head light switch as its source of power.

also, the brake light switch (which is being powered by the orange wire) feeds directly to the turn signals via the white wire.

BTW, there is simply no reason for the headlight switch to be grounded. think about it.

[fleetsidelarry]

Jon, here's an example of how sneaky this stuff is.

http://www.chevytalk.org/fusionbb/sh...rch/1/#2037863

not exacly the same problem as you're experiencing, I know.

Is the wiring to your headlight switch plug original?

[jonathan-m]

Okay, update number 2:
I realized that the headlight switches are interchangeable all the way up to '72, and they're cheap, so I went to the local store and just bought a new one just in case. Installed it, and the results were the same. No power to orange(stop light) and no power to brown (running light). headlights (blue) work, and then the turn signals also work. As I mentioned earlier, if I run a jumper from the red (power) to the brown then running lights do function, same goes for the stop lights, so the wiring itself is good.
Is there another ground point for the head light switch that I'm overlooking or something, the problem seems to begin at the switch.