Why the 1987 Toyota Pickup Wiring Diagram is a Pain
I spent a solid morning last year tracing a no-crank condition on a '87 4Runner that turned out to be a ground strap corroded to nothing. Three hours. Three hours because the only diagram I had was a faded photocopy from a $40 shop manual that showed the circuit but not which splice point under the dash was the actual failure location. The 1987 Toyota Pickup Wiring Diagram exists in multiple forms and none of them are particularly cooperative. You need to know which one you're actually looking at before you start pulling panels. The factory repair manual CD-ROM from Toyota is the closest thing to an authoritative source. It covers every system, every variant, and the legends are color-coded. The problem is it's dated and some connector views don't match the aftermarket harnesses that got slapped into these trucks over the decades. The diagram below will reference the factory layout. 
Free sources like forums and scanned PDFs float around, but most are from the 22R engine variant and won't account for the 22RE or the 3.4L V6. If you're working on an RE with fuel injection, a diesel diagram will send you down the wrong path for an hour. Don't trust a diagram until you've cross-referenced the connector pinout with an actual multimeter reading.
How to Actually Read These Diagrams
Toyota's wiring diagrams from this era use a system where the wire color abbreviation appears along the line. R means red, Bl means blue, W means white, G means green, Br means brown. Yellow is Y, Black is B, Orange is O, Pink is Pk, Green is Gr. They stack combinations like BR/W which is brown with a white stripe. The legend is usually on the first page of each system section. Pay attention to it because they switched conventions between 1985 and 1989. Ground points are marked with a G and a number. G100 through G115 or thereabouts. These are real physical locations. G100 on a 1987 22R is typically near the battery negative on the driver's side frame rail. G101 is usually at the firewall near the horn. G103 is behind the dash on the steering column bracket. When the diagram says "GND" it's pointing to one of these. Not a chassis ground you make yourself with a screw. The factory grounds are specific and the locations matter for resistance across the circuit. The connector numbers like C10, C20, etc. correspond to actual connectors in the harness. The diagram will show pin numbers 1, 2, 3, 4 going from one end of the connector to the other. Some connectors have locks and tabs that need to be depressed before you can back out the terminals. Pulling on the wires directly will break the terminal lock and then you'll be fishing for a 2mm tab with a dental tool at 11pm.
Get the Full Details
A Practical Example: Tracing the Charging System
Let's say your battery light comes on and you're measuring 12.6 volts at the battery but the alternator isn't charging. The diagram shows the B terminal on the alternator going through a 30-amp fuse to the battery positive. Then there's an I terminal that goes through a resistor and a warning lamp to the ignition switch. That I terminal is the field excitation path. If that circuit is open, the alternator won't self-excite. On my '87, the problem turned out to be a frayed brown wire at connector C13 under the dash, right where the harness bends against the steering column bracket. The insulation had rubbed through from steering vibration. The brown wire was the I-terminal feed from the ignition switch. I traced it by disconnecting the connector and probing each pin with the key on, looking for 12 volts at pin 2. No voltage there meant the break was upstream. I followed the wire back through the loom and found the damage two inches from the connector. Stripped the old section, soldered in a new length of 18-gauge wire, heat-shrunk it, and re-routed the harness away from the bracket with a zip tie about three inches forward of the bend. Charged within seconds. This is why the diagram is necessary. Without it, you're guessing which brown wire to test. With it, you know C13 pin 2 is the I-terminal feed and you go straight to it.
Common Pitfalls That Waste Time
The biggest issue with the 1987 Toyota Pickup Wiring Diagram is that many of these trucks have had their harnesses modified. Previous owners splice in alarm systems, stereo rewires, auxiliary switch installations, and LED light replacements without marking anything. A factory diagram will show a clean circuit. Your truck will have a crimp connector with electrical tape wrapped around it in a location the diagram doesn't acknowledge. Another trap is the variation between models. The SR5, the base model, the 4WD versus 2WD, the 22R versus 22RE versus the diesel 2C versus the V6 3VZ-E. Each has different circuits. The diesel has a glow plug system that doesn't exist on the gas models. The 4WD has an extra switch and relay for the engage solenoid. If your diagram doesn't match your exact engine and drivetrain, certain circuits will look different or be entirely absent. A third issue is the year-to-year changes within the generation. Toyota updated the charging system wiring between 1985 and 1987. The earlier diagrams use a different regulator setup. If you're reading a 1985 diagram on a 1987 truck, the alternator connector pinout might be wrong. Always verify the model year on the diagram matches your truck's VIN.
Tools That Make This Easier
A basic digital multimeter is non-negotiable. Something like a uni-t UT61E or even a cheap auto-range meter will work. You need voltage, resistance, and continuity modes. A test light is faster for quick checks but it doesn't tell you anything about resistance or intermittent opens. Pinout tools are worth the five dollars. Any hardware store sells a set of 1-millimeter and 0.5-millimeter probing pins. You insert these into the connector back side while the connector is plugged in. This lets you measure voltage at the terminal without damaging the connector. Using a multimeter probe to poke through the insulation is a shortcut that creates more problems than it solves. Eventually you'll push the terminal out of the lock and the connector will be loose on the part it's connected to. A harness light circuit tester can save you hours on ground faults. It's a device that sends a signal through the harness and tells you which circuit has a short to ground. For a total no-go situation where nothing works, this is faster than tracing every wire by hand. I got one on Amazon for about $25 and it's paid for itself three times over.
When the Diagram Isn't Enough
Sometimes the diagram is correct and the truck still doesn't behave. This happens when the wiring has been modified so thoroughly that the factory diagram no longer represents reality. In those cases you have two options. You can trace the actual wiring with a multimeter and build your own reference, or you can replace the entire harness with an aftermarket reproduction. Aftermarket harnesses from companies like Toto's or American Auto Wire exist for these trucks. They're not cheap but they come with updated connectors and better insulation. The downside is they may not match the factory color code exactly, so you still need the diagram to identify which wire does what. The upside is you eliminate decades of previous owner modifications from the equation. There's also the option of taking photos of every connector in your current harness, labeling them, and building a personal reference document. It takes a few hours of stripped-down dashboard work but it becomes invaluable the next time something goes wrong. The factory diagrams are static. Your truck's actual wiring is dynamic and evolves with every repair.
Quick Reference: Common Ground Locations on a 1987 Toyota Pickup
G100: Driver's side frame rail, near battery negative G101: Firewall, passenger side, near horn G103: Steering column bracket, behind dash
G104: Behind left kick panel G105: Under dash, center near brake pedal G106: Frame rail, passenger side, forward of firewall
G107: Transmission tunnel, near starter G108: Engine block, passenger side Clean these connections. A corroded ground at G103 can cause intermittent dashboard lights, erratic gauge behavior, and charging system complaints that have nothing to do with the alternator. Sand the contact point on the frame, apply dielectric grease, and retorque to spec. This alone fixes a surprising number of electrical gremlins on these trucks.
Download Resources
The full factory repair manual PDFs circulate on Toyota forums. The 1987 model year documentation is split between the 22R section and the 22RE section. Make sure you download the correct one. Some hosts require registration. Archive.org has copies of the original printed manuals scanned at decent resolution. A printout of just the wiring pages at 100% scale is often more usable than a screen because you can lay it across the engine bay and match wires visually. If you're looking for a single comprehensive 1987 Toyota Pickup Wiring Diagram file, search for "Toyota Repair Manual 1987-1995 PDF" on the official Toyota owner portal or licensed manual vendors. Third-party sites often have outdated or incomplete versions. The factory manual will show every circuit in the truck, not just the engine wiring. That matters when you're dealing with accessories like the air conditioning clutch circuit, the fuel pump relay, or the immobilizer system that varies by trim level. The diagrams are technical by nature. They're not designed to be read like a novel. Pick a specific problem, find the relevant system section, and trace the circuit from power source through switches and relays to the load and back to ground. That's the process. Nothing about it is fast on the first attempt, but it gets faster once you learn where everything lives in the harness and which connectors tend to fail on this platform.
