A little late to the party I see. I’ll address the issues as well as I can in the order that you expressed them.
1) You need to, at least, narrow down the area from where the “clicking” noise under the dash is emanating. Try unplugging the blower motor to see if the noise stops.
2) What are the circumstances surrounding the right front turn/marker lamp wiring, such that you need to touch wires together?
3) The rear lights feed through the narrow 7-cavity plug along the left side of the bulkhead connector. Only four of the cavities are used for the yellow (left turn/brake), dark green (right turn/brake), brown (tail/marker), and light green (backup) rear lamp wires. Probe the connector with your test light from the engine compartment side to see if power is passing through the bulkhead to the rear lamp harness as the associated circuits are energized. If power passes through the bulkhead connector, move to the rear of the truck and probe the rear lamp connector(s) for power. Proceed from there.
As a matter of standard routine, inspect the full length of the rear lamp harness from the bulkhead all the way rearward for obvious physical damage. Be especially alert to the condition of the harness where it passes close to the exhaust and over the top of the rear axle tube. It’s common for the rear harness to melt from exhaust heat and/or chafe and sever from rubbing against the top of the axle tube if the plastic clips that retain the harness to the inside of the frame rail have broken.
4) The current through the 5-amp INST LPS fuse is adjusted by the dash lamp dimmer rheostat. As the rheostat is rotated from stop to stop, power to the fuse will vary from near zero to near battery voltage. Rotate the headlamp switch knob fully CCW and the test light should illuminate to near full brightness.
5) An incandescent test light will illuminate only if there is a suitable voltage to do so. Probing an otherwise good circuit will not illuminate the test light if the circuit is switched off, or if the test light is not properly grounded. If a circuit doesn’t illuminate the test light, work your way back toward the switch that controls power to the circuit. Continue to the power source feeding that switch, if necessary. As long as you remain systematic and methodical, you will accurately determine where/why power is interrupted.
6) When it comes to wiring repairs, you first need to ascertain the full extent of damage. Mike81K10 provided sound guidance. Expanding his counsel, your approach to a viable repair strategy (e.g., sectioning and splicing of wires vs wire run replacement vs a complete service harness swap) depends on multiple factors, foremost among them are the extent of existing damage, comparative repair/replacement costs, the urgency in returning the vehicle to service, availability of the proper materials, and personal expertise (or the willingness and finances to gain experience in its absence). Needless to say, the more experience you gain, the more accurate your evaluations and the easier your choice of repair strategy will become.
Replacing/repairing a few wires can be straightforward or tedious, depending on location and accessibility. Unless you are only 18" tall (in which case you might need a ladder), it’s not fun to contort under a dash, especially for extended periods. Nonetheless, a properly spliced or replaced wire, using good technique, is as effective and durable as factory new. On the other hand, repairing/replacing a bundle of wires, one-at-a-time, can be time consuming and both physically and mentally trying. Constructing a 20-plus-wire harness with many exit points and complex routing, without the use of a wiring jig, can outright test your patience by presenting confounding configuration challenges and redoes, not-to-mention surprise you with the outrageous cost of materials and tooling for a proper outcome. Yet, for contrast, a brand new service harness can be initially expensive and not without hidden challenges. Often, service wiring harnesses must be custom tailored to specific circumstances because of mismatched connectors and/or missing circuits. Essentially, you have to work within the confines of your budget, skill, and comfort zone.
But, don’t let my blog-like rambling dissuade you. DIY electrical work, properly and thoughtfully executed, can bring a well earned feeling of great satisfaction and increased ability. It only seems difficult in the beginning before you prove to yourself it is both understandable and doable.
7) You asked,
“Am I wrong in assuming that if the truck starts, the bulkhead should all be working and should get electricity to where it needs to go once grounds and proper connections are checked/fixed?” That assumption is incorrect. There are many wires that pass through the bulkhead plug that have no connection to or bearing on engine startup and running. Windshield wipers, B+ feed for lights, brake warning, charge indicator, horn, forward lamps ... all pass through the bulkhead plug. If you peruse the factory wiring diagram for your specific truck year and model it should become evident.
8) In closing, electrical effects are not magical. Electricity appears mysterious only when one is missing the very few fundamental concepts that define it. Three fundamental elements of automotive electricity that are crucial to grasp are voltage, current and resistance.
- Voltage represents an accumulation of electrically charged subatomic particles at a specified location.
- Current represents a migration of electrically charged subatomic particles from one location to another.
- Resistance represents a physical restriction that limits the migration of electrically charged subatomic particles.
In different words, voltage is the amount or density of electric charge, current is the migration of electric charge from one point to another, and resistance is a limiting effect that impedes the migration of electric charge.
For example, imagine that each electrically charged subatomic particle is modeled by a small round BB. By adjusting the number of ‘BB’s’ at any given location, you can control the voltage at that location. Now, imagine transferring a spoonful of BB’s from a location of high BB concentration, across a distance, to a different location with low BB concentration. The activity of moving the BB’s from one location to the other in the manner described represents a pulse of current flow. Next, move that same spoonful of BB’s to a third location by funneling them through a straw. The small diameter of the straw is analogous to resistance that limits the transfer rate of the BB’s. Ponder the gist of this paragraph for a few moments.
Using your mind’s eye, mock up BB’s amassing in a region. Move the BB’s (discrete electrical charges) through various sized resistances to new regions, always from higher charge concentration (high charge density) to lower charge concentration (low charge density), with the end goal of equalizing the charge density across all regions. This mental exercise gives you a crude analogy to the mechanics and interplay of voltage, current, and resistance.
Referring to the example just provided, in any useful circuit, voltage, current and resistance are intimately and unavoidably related and interactive. Each affects the remaining two in a precise balance. Effectively, voltage and current are two manifestations of the same thing (charge), while resistance is the bridge between them.
Of course, there are other analogies that can be used to demonstrate voltage, current and resistance. Some that are more representative. But BB's will suffice as long as you don't scrutinize.
Due to the nature of charge, voltage is compelled to distribute laterally such that charge becomes uniform (the same) everywhere, establishing an equilibrium of charge density. It’s this property of charge that makes electricity useful. Charge always flows from a point of high accumulation (high voltage) to a point of low accumulation (low voltage). The rate of charge flow or redistribution is the current. Therefore, voltage and current are two means to quantify the condition of charge, whether static (simply accumulating) or moving (actively redistributing).
The relationship between voltage, current, and resistance is exactly and precisely described by Ohm’s Law, which mathematically states that
Voltage (in volts) equals
Current (in amperes) times
Resistance (in ohms):
V = CR.
Ohm’s Law assures that:
- If voltage increases (decreases), then current and/or resistance must also increase (decrease), maintaining a precise proportional balance.
- If current increases (decreases), then voltage must simultaneously increase (decrease) and/or resistance must simultaneously decrease (increase), always in proportional balance.
- If resistance increases (decreases), then voltage must simultaneously increase (decrease) and/or current must simultaneously decrease (increase), again, always in a precise proportional balance.
The key relationship to grasp from all of this is that
voltage is directly proportional to current and resistance, whereas current and resistance are inversely proportional to each other. That is, if voltage is held constant and current increases, it is only because the resistance decreases proportionally. Similarly, if circuit resistance is constant and voltage decreases, the current flow also decreases in proportion to the drop in voltage. And, so on. Get the idea?
Rarely will you use Ohm’s Law for actual calculations in routine practice. BUT, understanding the relationship between voltage, current and resistance and how they interact and affect one another is invaluable to electrical diagnoses and correctly interpreting symptoms!
There is a caveat, however. If there is an error in the ground path, all manner of chaos will result and logic will disintegrate! GROUND MUST BE PERFECT AND AT ZERO for proper circuit function to occur! So what
is ground? For convenience and by convention, the point of lowest charge accumulation (lowest charge density) in any circuit is defined as ground, which is normalized to a “zero” value. Assigning ‘zero’ to ground creates a stable frame of reference for managing predictable circuit operation. Consequently, all voltages in any given circuit are measured with respect to ground (zero). Electrical ‘ground’ borrows its name from the ground of Earth, which is assumed to exhibit zero voltage.
Voltage, current, resistance, and ground are four fundamental circuit elements that MUST be understood. In addition, a working knowledge of two of the fundamental laws of electricity will benefit you greatly.
- Kirchhoff’s Current Law states that CURRENT IS ALWAYS CONSERVED AND NEVER CONSUMED. However much current enters a circuit or junction must simultaneously exit that circuit or junction. Current in always equals current out.
- Kirchhoff’s Voltage Law states that 100% OF THE VOLTAGE APPLIED ACROSS A CIRCUIT IS CONSUMED BY THAT CIRCUIT. However much voltage that is applied to a circuit is proportionately consumed by every component of that circuit that exhibits resistance. Voltage is used such that the supply voltage proportionally drops across each component in turn, eventually reaching zero at ground.
So there you have it. The six basic concepts that are fundamental to understanding automotive electrical circuitry. Of course there are definitions, corollaries, lemmas, and such that fill in the minor voids and inconsistencies for a perfect understanding, though I’ve never met the individual who knows them all. They are the types of data that you learn as you need to know them
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