Okay, let's troubleshoot your trailer brake issue systematically. You've done some good initial checks, but we need to dig deeper. Given the symptoms you're describing, here's a breakdown of potential problems and troubleshooting steps

Understanding the System
Factory Integrated Trailer Brake Controller (ITBC)

Your Silverado's ITBC is a sophisticated system. It doesn't just apply a fixed voltage. It senses the truck's deceleration and dynamically adjusts the voltage to the trailer brakes. This modulation is crucial for smooth and controlled braking.

Pulse-Width Modulation (PWM)

The ITBC likely uses PWM to control the brake voltage. This means it's rapidly switching the voltage on and off. A simple multimeter might not give you a steady, easily readable voltage unless you're specifically set to measure duty cycle or you have a scope.

Communication

Modern systems often have communication protocols (like CAN bus) involved with the ITBC. The truck's computer needs to know the trailer is connected and how it's braking.

Troubleshooting Steps1. Confirm Trailer Connection



Trailer Type

Ensure the truck is configured to recognize a trailer and not just a lighting connection. In the truck's settings, there's usually a menu for trailer settings where you can select the trailer type (electric brakes).

'Trailer Connected' Message

Verify the dash display shows that a trailer is connected when the trailer plug is inserted. If it doesn't, the truck doesn't know to activate the ITBC. Clean the pins on the truck and trailer connectors thoroughly. Use electrical contact cleaner. A small amount of corrosion can cause significant problems.2.

Ground Issues - Critical



Isolate the Ground

Disconnect the trailer. Now measure the resistance between the truck's trailer connector ground pin and the truck's frame. This should be very close to zero (less than 1 ohm). If it's high, you have a bad ground. The frame is the best ground point, not just a random spot on the body.

Ground Wire Inspection

Trace the ground wire from the trailer connector to its grounding point on the truck frame. Look for corrosion, loose connections, or breaks in the wire. Clean and tighten the grounding point.

Multiple Ground Points

It's possible the trailer has a separate ground connection to the truck's frame (in addition to the one through the connector). Check for this and ensure it's also clean and tight.3.

Fuse Verification - Deeper



Voltage Drop Test

While you've confirmed 12V at the fuse, perform a voltage drop test under load. Connect a test light or a small load to the trailer brake circuit (at the connector, with the trailer disconnected to avoid damaging the trailer brakes). Measure the voltage at the fuse while the load is active. If the voltage drops significantly (more than 0.5V), the fuse or the wiring to the fuse may be corroded or have high resistance.

Fuse Type

Double-check that you have the correct amperage fuse installed. Refer to your owner's manual.4.

Connector Inspection and Cleaning



All Pins

Inspect all pins on both the truck and trailer connectors for corrosion, bent pins, or damage. Use a small pick to gently straighten any bent pins. Clean the pins thoroughly with electrical contact cleaner.

Connector Body

Check the connector body itself for cracks or damage that could allow moisture to enter.5.

ITBC Gain and Output Check



Gain Setting

Make sure the ITBC gain is set appropriately. Start with a low gain setting and gradually increase it. A gain of "0" will produce no output.

Hand Controller Voltage

With the trailer connected and the truck recognizing the trailer connection, use a multimeter to measure the voltage at the trailer brake pin (with respect to ground) while slowly applying the manual override (hand controller). The voltage should increase as you apply the hand controller. If you get no voltage, even with the hand controller fully applied, the ITBC itself may be faulty.

Monitor the Display

Pay close attention to the truck's instrument panel display while using the hand controller. It should show the braking output increasing. If it shows "Check Trailer Wiring" or a similar error, that's a strong indication of a wiring or connector problem.6.

Brake Controller Calibration

Some ITBC systems require a calibration procedure when a new trailer is connected. Consult your owner's manual for the specific procedure. This usually involves driving at a certain speed and applying the manual brake controller.7.

Trailer Wiring (If Possible to Test)



Direct Connection

If you have access to the trailer wiring, try applying 12V directly to the trailer brake wires (with the trailer disconnected from the truck, of course). This will confirm whether the trailer brakes themselves are functioning. Use caution and start with a low voltage to avoid overpowering the brakes.

Trailer Connector Check

Use a multimeter to check for continuity between the trailer brake wire at the connector and the brake magnets themselves.8.

Scan for Codes

Use an OBD-II scanner that can read body control module (BCM) codes. There may be codes related to the ITBC or trailer wiring even if the dash doesn't show a warning light.

Addressing Your Specific Observations 100 Ohms Resistance on Ground

This is definitely a problem. A good ground should have very low resistance (ideally close to 0 ohms). This is the most likely cause of your issues.

No Continuity From Fuse to Plug (With Hand Brake Engaged)

This could be normal if the ITBC is not active (i.e., the truck doesn't think a trailer is connected). It's also possible the ITBC is faulty and not outputting voltage. The lack of continuity could also be that the ITBC needs some kind of signal to output voltage, or is using PWM which makes testing difficult with a standard multimeter.

Important Safety Notes



Disconnect Battery

Whenever working on electrical systems, disconnect the negative battery terminal to prevent accidental shorts.

Proper Tools

Use appropriate tools for electrical testing, including a multimeter, test light, and wire strippers/crimpers.

Consult Manuals

Refer to your truck's owner's manual and any available wiring diagrams for the trailer brake system.

In Summary:

Start by thoroughly cleaning and inspecting all connectors and ground points. Fix the high ground resistance first. Then, verify the truck is recognizing the trailer connection, and test the ITBC output while applying the hand controller. If you're still having trouble, consider having a qualified technician diagnose the system. A shop with the proper scan tools can see what the computer thinks is going on and might even be able to perform tests on the brake controller. Flag for review