Bugging Vehicles

Instructor’s Guide to Bugging Vehicles


Having well thought out and properly prepared vehicles is the key to a successful hands-on field exercise. This guide will provide the basic instructions to install simple bugs in most makes and models of vehicles.

Training Concept 1

Learn how to properly test and swap a relay, check for blown fuses, and to test circuits and components with a DVOM and logical diagnostic routines. These exercises are intended to reinforce electrical circuit knowledge, test equipment usage, and relay operation and pin identification. Application of diagnostic steps and on-the-go solutions for the fuel, ignition, cranking and charging systems also will be reinforced using these same bugging techniques.

Methodology to Reinforce:

Create an open circuit inside the relay to be tested, or in the external circuit that switches the relay on and off. Have the trainees perform appropriate diagnostic tests according to the RPST Participant’s Guide troubleshooting chart. Bugs of these types may be used to create a variety of “no-crank/slow crank” or “cranks, no start” scenarios, depending on what components are available and accessible on the vehicle one is working with.

Tests and fixes include:

• Basic visual checks
• Check for blown fuses with a test light or DVOM
• Check for voltage to the relay with a DVOM
• Check for relay “click” when turned On
• Identify relay pins connected to the operating circuit according to the Participant’s Guide or Quick Reference Guide charts. Test for power to the relay with the DVOM, swap relays to operate the component temporarily.
• Identify identical, non-critical relays and swap with the suspect relay.
• Identify relays that should not be swapped and left installed in a different location, such as the cooling fan and horn relays.

Bugging options:

• If using a spare relay, gently pry off the cover and cut one wire leading to the hold-in coil. Reinstall the cover so it cannot be seen that the relay was disturbed. The relay will not “click” when it is turned “On” and both the control circuit and operating circuit will remain open.

• If the relay must be returned to service, gently pry off the cover and place a small piece of thin cardboard, such as from a matchbook cover or business card, between the contact points. Reinstall the cover so it cannot be seen that the relay was disturbed. The relay will now “click” when it is turned on, but the operating circuit will remain open. The component being operated by the relay (fuel pump, starter solenoid, etc.) will not work.

• Using a wiring diagram and/or the vehicle owner’s manual, determine if there is a fuse that will disable the control circuit for a given relay. For example, the “Crank” fuse found on some GM models will disable the starter relay, causing a no-crank condition. The “Ignition” fuse on some Ford models will interrupt several circuits, including the starter relay, warning lights and other functions wired through the ignition switch. Using jumper wires, short a spare fuse across the battery to blow it. Then, install the blown fuse in place of the good fuse in the vehicle fuse panel.

• Disconnect the Neutral Safety Switch (Range Selector) on the automatic transmission or clutch pedal on a manual-shift vehicle. The starter will not crank and the starter relay will not click, but a jumper, such as a screwdriver blade, may be used to bypass directly at the starter solenoid, if accessible. This bug may also be used to demonstrate shift interlock override techniques, as the shifter will not release from Park on most models. Depending on the exact vehicle model, it may or may not be driveable with this malfunction, even if the engine is started.

Training Concept 2

Learn how to identify poor connections and open circuits at the vehicle battery connections. These exercises are intended to reinforce electrical circuit knowledge, test equipment usage and visual/tactile inspection techniques.

Methodology to Reinforce:

Create an invisible open circuit at one of the main battery connections or a main fuse. Have the trainees perform the “Slow Crank/No Crank” series of diagnostic tests according to the Participant’s Guide troubleshooting chart.

CAUTION: This bugging procedure may erase stored memory codes for the radio, some accessories and possibly the PCM as well. It should not turn on the MIL, however. If you are bugging a vehicle that is to be returned to service, be sure to capture and record any radio or other security codes. Also, write down the preset radio stations on all bands. At the conclusion of training, reset the clock and radio presets before returning the vehicle to its owner. Offer to assist in reprogramming sliding doors, sunroof, etc. Double check to make sure the MIL is not on when the vehicle is running. If it is, reset the trouble codes using a scan tool/code reader or offer to have it done at a local repair facility.

Tests and fixes include:

• Basic visual checks
• Testing for blown main fuses or fuse links with a DVOM
• Voltage Drop testing with a DVOM to identify an open or weak connection
• Testing for battery power to starter, fuses, and battery cable clamps with a test light
• Retrieve and reset radio presets and security code(s)
• Reprogram electronic accessories

Bugging options:

• Using a vehicle with a post-type battery. Disconnect one battery terminal. Then, place a layer of Scotch tape around the exposed battery post. Gently reinstall the cable clamp over the tape. In most cases, this will provide a completely open battery connection. Occasionally, a very small connection may exist, which will provide even more fun, as the instrument panel lights may light when the key is switched on, but everything will go “dead” as soon as cranking is attempted. This situation actually happens quite commonly in the field, but not usually with what appear to be clean and tight terminal connections!

• Identify a main fuse that supplies power to numerous circuits including the cranking system. Blow a spare fuse as described previously in Training Concept 1 and place it in the fuse panel in place of the identified main fuse.

• Identify and disconnect a main “feeder” connection leading from the battery to a fuse/relay panel. A good example is the in-line connector found near the battery on older model Chrysler products, which leads straight to Battery Positive. These connectors can be backed out just enough to open the circuit, but still appear as though they are connected.

Training Concept 3

Learn to check ignition system operation on designs with distributor, coil packs with wires, and coil-over-plug.

Methodology to reinforce:

Create no-spark conditions on a variety of vehicles to allow trainees to experience as many design variations and problem causes as possible. If possible, include at least one vehicle of each basic ignition system design: single coil with distributor, coil packs with no distributor, and coil-over-plug.

Tests and fixes include:

• Basic visual checks
• Testing for spark into and out of a distributor cap
• Visual test for distributor shaft rotation
• Determining the order of ignition system tests, depending on accessibility of components
• Testing for blown fuses, open circuits, disconnected components
• Temporary electrical “short to ground” repair with nail polish

Bugging options:

• With a single coil and distributor ignition system, drill a hole in a spare rotor underneath the center contact to simulate a rotor that is shorted from burning through to the distributor shaft. Have the trainees use an inductive timing light and/or spark tester to check for spark “in” and “out” of the distributor cap. Disassemble the distributor and use nail polish under the rotor to effect a temporary repair. The same spare rotor may be used repeatedly by scraping off the dab of nail polish and re-drilling the hole.

• With a single coil and distributor ignition system, disconnect the ignition module or install a blown fuse in the PCM circuits to “kill” the coil’s ability to trigger and fire the plugs, but still have power supplied to the coil positive (+) terminal. Have the trainees use a DVOM check for power to the coil.

• On a vehicle having a distributorless ignition system with plug wires, disconnect the crankshaft and/or camshaft position sensor. Have the trainees test for spark with the inductive timing light or spark tester and follow diagnostic steps shown on the Participant’s Guide troubleshooting chart.

• On a vehicle with coil-over-plug ignition, install a blown fuse or bugged relay to disable power to the ignition coils. Have the trainees use the inductive timing light to check for spark, and follow general electrical troubleshooting procedures to find the bad fuse or relay as in Training Concept 1 above.