Tail lights / Marker lights

[Hevychev76]

New wiring harness installed, new headlight switch, dimmer switch and turn signal switch. I have headlights Hi/low beam, turn signals and 4 ways and brake lights all work but no running lights. I have removed the plug to the headlight switch  and run a jumper wire from the main red power wire for the switch to the brown wire for the running lights and then they work but not at all through the switch.... sure could use some advice, Jeff

[bd]

Using a test light, check both sides of the "TAIL LPS  CTSY" fuse.  The tail/courtesy fuse feeds the orange wire to the headlamp switch, which in turn powers the tail lights and dash lights.

[flips87c30]

Im having the exact same problem. No tails or running lights. checked the fuse and its fine. going to check the orange wire bd described this evening. I will post anything I find and check back here for any other ideas.

[bd]

@ Both...

Even when a fuse looks and checks good, minor corrosion between the fuse and its terminals in the fuse box can prevent power flow.  So, always check fuses by probing the fuse box terminals with your test light, as well as the accessible ends of the fuses.  Make sure that wire connections to the headlamp switch are clean and tight and that there's no visual evidence of heat stress or damage to the switch, its wire connections, or the plastic harness connector.  If the dash lights aren't illuminating either, read Diagnosing dash lights that don't work for supplemental information.


@ Hevychev76...

Refer to the 1976 Wiring Manual in our Technical Pages.  Allow a few minutes for download and save to your hard drive for faster access in the future.


@ flips87c30...

Refer to the 1987 Wiring Manual.  Do the running lights work when you temporarily jumper battery to the brown wire at the headlamp switch? 

[flips87c30]

I actually jumped from the brown wire that comes out of my firewall to make the lights work. I stripped away just enough to make a connection. I know thats not the best way to do things but I had to use the truck for work. I used my multimeter to check voltage at the fuse block, it all checks out, the fuse was fine as well but I put in a brand new one anyway. Im leaning towards a bad ground somewhere.

[bd]

@ flips87c30...

Think about what you just posted.  The lights work when you bypass the headlamp switch and under-dash wiring....

Your truck has a power feed problem!

By all means verify the vehicle grounds.  Since they are a common source of grief, grounds should be checked periodically and maintained.  But, focus on the headlamp switch and under-dash wiring to solve the existing running lamp problem.

     ...And, you will need to do something about that bare wire at the firewall to prevent moisture intrusion and subsequent corrosion, especially if you drive salted roads!

[flips87c30]

Lol I have been thinking about what I posted since I posted it. Im just not very knowledgeable about wiring. Its good to talk it out with someone who knows what theyre talking about. Thanks for the input I will let you know what I find

[bd]

That wiring manual I linked is your friend!  Become familiar with it and refer to it often. 

...Learning the nomenclature of schematic diagrams will electrify your life....   

[flips87c30]

Another question... I used my multi meter in the fuse block, in place of the tail/ctsy fuse, when I pull the headlight switch I get 12 volts. Im guessing that's how it should work. So Im thinking my problem is between the fuse block and the firewall. but I don't see anything obviously wrong, I guess I will have to dig deeper

[bd]

DON'T USE YOUR VOLTMETER AS AN AMMETER ! ! ! ! ! !

Use your voltmeter as a VOLTMETER!

Although the exact amount of current is dependent on the impedance of your particular meter, incredibly small current flow through a voltmeter will drive the meter to indicate full system voltage.  Based on what you've posted so far, there could be (and probably is) a burned/poor connection with excessive resistance sufficient to prevent the running lights from illuminating, yet still allow your voltmeter to read 12 volts.  Many people make this mistake when using meters.  That's why I generally recommend using an incandescent test light for diagnosing simple power and/or ground problems.

Voltmeters are intended to be connected in parallel... hence, you measure voltage across a circuit or component, never through the circuit or component.  Connecting a voltmeter in series will totally misrepresent what is occurring within the circuit.

Do this:  Focus on the headlamp switch and its connections.  With the wiring harness plugged into the headlamp switch, turn the switch ON and connect your voltmeter between the orange wire feeding power to the switch and the brown wire going to the running lights.  What's the voltage reading?

[Hevychev76]

Thank You BD for your response, I have solved my issues with the lights thanks to you. I've installed an after market wiring harness to save a little bit of cash (should have just ponied up the cash for the correct one but oh well) anyway my thoughts on what the orange wires were for the dome light but when I fed power to them like you described everything works like it should.... now off to the a/c and wipers :-)

[bd]

Happy to help!