The circuit for park/ marker lights does indeed go "thru" the light switch.

 

Here,
__read this.

Odd Electrical Behavior, Blinking Lights, Dim bulbs, Flashing Lights, Bad Gauges etc.
By: Torque1st
--------------------------------------------------------------------------------

For many of the crazy electrical problems on these old trucks the problem can be traced to bad grounds. Remember it takes a complete circuit in order for electricity to flow. A bulb or socket may no longer be grounded due to corrosion. An entire fender may not be grounded due to rust. Check the body and frame ground points and cables, Many aftermarket battery cables do not have a ground tab on them that was used to ground the body and frame like the OEM cables did. Clean all connections to bare metal and coat them with silicone dielectric grease. Use internal or external tooth lockwashers as appropriate to help maintain electrical contact. The lockwasher provides a little "spring" to the connection that will help maintain electrical contact during heat/cool cycles. Make sure the body panels, cab, frame, and engine are grounded.

A battery cable that looks good can have corrosion between the cable wire strands and the terminal body. I have been making all of my old battery cables from those lead free terminals and welding cable or standard battery cables. I cut the factory ends off cables and make my own connections. Most replacement battery cables have very thin crimped terminals on the end with a larger hole designed to go over the typical 3/8" Chevy style terminal studs. There is very little wire left when that large hole is punched thru. Proper terminals with a 5/16" hole can be purchased from hardware stores, welding shops, or even "home box" stores. The good terminals can be crimped on and soldered properly. Some electrical or welding shops will crimp on terminals for a fee.

Most of the wire terminals and connections in these trucks are crimped at the factory. Factory crimping is a good process but failures can occur. The electrical systems in these trucks were designed to last about 5 years, maybe 10 at the outside. -Or maybe just thru the warranty period. Those crimped terminals have been exposed to thousands, perhaps millions, of temperature changes and heatings due to current flow and ambient temperature changes. Every time current flows or the metal heats up they expand and contract and the wire expands and contracts at a different rate than the connector body. This tends to loosen the connection which creates a higher resistance and more heat. The higher the temperature the more the metals expand and react with atmospheric and environmental contaminants which produces corrosion. Corrosion causes an increase in resistance which produces more heat in a vicious cycle. These electrical systems are OLD! Tiny amounts of corrosion can cause the engine gages to malfunction. The voltage drops in wiring connections cause the headlights, turn signals, and other lights to be dim.

The only "cure" for this aging process is to disassemble the connectors and wiring harnesses. Every crimp and connection has to be examined, cleaned, re-crimped, and soldered. Some may have to be replaced. Solder any replacements. When the wiring connectors are reassembled coat the contact surfaces with silicone dielectric grease, the same stuff that is used on spark plug boots. This helps to seal out environmental contaminants, moisture, and oxygen from the connections. They will still make metal to metal contact. Very dilute muriatic acid will clean electrical connections just rinse very well. Even toilet bowl cleaner etc will work if it has acid in it.

For high temperature connections like headlights and blower motor resistor connections use high temperature connectors available from appliance repair shops. They use them for wire connections to heating elements. The standard crimp connections found in stores will not last long with the heat exposure in these connections. You can solder those crimp terminals with silver solder also. Silicone dielectric will boil off of these connections but I sometimes use it anyway.

Crazy Dash Gages:
--------------------
I do believe that we must realize these instrument systems are 25-30 years old and were never designed to operate more than 10 years at the outside. The instruments operate on a very small amount of current and low average voltages so any amount of oxidation on any of the connections will cause them to read wrong. To make the Ford gages read properly for many years to come all you have to do is clean ALL of the connections and protect them from corrosion and oxidation with a little silicone dielectric grease. Once you have done this they will operate great!

The Instrument Panel Voltage Regulator (IPVR) is hard to check since it is just a thermal "flasher" unit just like a HD turn signal flasher. The output voltage goes to 12V and ground in a pulse fashion. Supposedly it averages out to 5V but it takes an O-scope to see the pulses and average the voltage. If the IPVR has a bad ground it will supply full battery voltage to the gages causing them to peg to the right at times, sometimes continuously. This is the most common failure mode. Clean the connection as described below and use a star washer under the IPVR retaining screw to help maintain pressure on the joint. Eventually the plastic will creep and the joint will lose contact again tho.

The flex circuit on the back of the instrument cluster can be cleaned with a variety of methods. Remove the flex circuit and very gently brush the contact surfaces with a fiberglass spot abrasive brush found with the touch up paint at the parts store or some people use a regular #2 pencil eraser. Very gentle cleaning is required, if you remove too much copper the circuit is ruined. Use a damp paper towel to clean up the dust afterward. Coat the contact surfaces with a thin layer of silicone dielectric grease and reassemble the panel.

Ordinary crimp connections can be cleaned with brake cleaner then dipped in a dilute (1 part in 10) solution of muriatic acid available from the hardware store. Rinse the connector thoroughly in running tap water. Blow out with compressed air or blot dry with a paper towel. Solder the connection. If the connection has been properly cleaned solder will wick into the joint. This will not work with a connection that is obviously overheated or corroded. Replace those connectors.

--------------------------------------------------------------------------------

 

Go to your steering column where the color of wires that I gave come out of the column. There should be a connector there also. Check there for Power with tailights on and then turn signals on. If you have power there then it's between there and the tailights and has to be a corroded connector or a ground. I would then go through the above process checking each connector, and then again the grounds. I would take each ground loose if necessary clean both contact points good and reconnect.

 

Does the rear side marker lights work? This is the brown wire, i.e. running lights...and it does goes straight from headlight switch as quoted above.

Do you have brake lights when you press the brake?

I am just trying to narrow down and make sure I am giving you the right colors and understand your problem 100%.

 

Also should have asked...

Do you have front side marker lights and park lights?

Do you have rear regular park/tailights with headlight switch on?

Sorry as I may have misunderstood the original problem....reading again it looks to be no taillight, and then no rear turn signals, but please answer all of the above questions to help. Also if I am correct in understanding the problem then it will require 2 separate fixes.

All of these (marker and park light/taillights, front and rear) are controlled by the BROWN wires directly from the headlight switch. Check the Brown wire with the headlight switch on, right before the wire enters the tailight. If you have no power there, check for power on the two Brown wires coming out of the back of the headlight switch on the dash. Do you have 12v there with the headlight switch on? Sorry I may have misunderstood the original problem....reading again it looks to be no taillight, and then no rear turn signals. If that is the case should be two separate fixes. The running lights do not run through the turn signal switch in the column, all other turn signal/brake lights do. To check the REAR turn signals, check the green wire, and the yellow/black wire with the turn signals activated. You should be getting a pulse on / off on you circuit tester, and with brakes applied you should be getting a solid light. If you are getting nothing, do the same check at the base of the steering column where the green and yellow/black wires exit the column. Activate the signals and check for voltage. If you have none, I would say bad turn signal switch in steering column.

The front turn signals are controlled by a different color wire, green/wht and wht/blk or wht/blue.

 

I've had the same problem recently...my brake and turn signals quit working.

I searched for a bad ground and followed schematics for a while before I realized it was pretty hopeless...after 35 years of owners messing with the wiring harness, this thing is rat f*^$ed!

Here's a crazy idea but I thought I'd mention it cause it was the simplest fix for me....

I took the brute force method and ran new wires with bulbs to the front and rear lights I needed and installed a switch panel on the bottom of the steering wheel column. The panel has three switches, left is left turn, middle is brake and right is right turn signal. It works great and was easy to install! This is just a temporary fix though, I'm going to replace the entire harness in the next few years after I finish school and get the chance to tear my truck down...and rebuild

Its just an idea

 

It could cause the taillamps to go out yes. (IE: headlamp switch)

Check to see if your other marker lamps are working. Side marker, licence lamps, and front markers. If none of these work, the it's pointing directly to the light switch.

Coupled with the fact that your instrument cluster illumination used to be intermittant at best, before it quit, I'd replace that light switch anyway. Seems to be worn out.


As for hazards and brake lamps working, but no turn signals, this points to either the turn signal switch, turn signal fuse, or turn signal flasher. The hazard lamps, brakes and turn signal lamps are on the same circuts when they leave the turn signal switch, so if you have brake and hazards you still have a connection from the column back to the lamps.

Do these steps...


1: check the fuse to the turn signal switch, make sure it's not blown. Don't just look at the fuse, test and make sure with a tester. If the fuse is good, go on to the next step.

2: check the turn signal flasher, Remember there are two flashers, one for turn and one for hazards. remove the hazard flasher and put it in the turn signal flashers place to test. if your turn signals start to work, replace the flasher.

3: check for power at the turn signal switch with the ignition key in the on position. You can check at the horseshoe connector at the bottom of the column.

If you have power at the blue wire at the switch, then the turn signal switch needs replacing.

There is a metal piece inside the switch that connects the lever to the other connections inside the switch. This piece likes to break off causing this type of failure.

It sounds like you have multiple problems that are not connected to each other.


EDIT: ------------------------

Just read that you have working front turn signals, brake lights and hazards but no rear turn signals. This definately means your turn signal switch is defective and must be replaced.

------------------------------

Hope this helps

 

Agreed as I stated above. High probability bad headlight switch and turn signal switch, especially with him having dash light problems also as they are on a different circuit.