In a tractor of the type having a cab, an internal combustion engine, an electrical system, an ignition switch, a fuel pump, one or a plurality of door light switches, and an electrical power supply, a tractor-trailer alarm system comprising:
- at least one arming switch which is positioned to arm said alarm system;
- at least one sensing switch associated with a portion of the tractor, said switch being normally in a first, electrically non-conducive position indicating that the corresponding portion of the tractor is undisturbed and being actuable to a second, electrically conducive position when the corresponding portion of the tractor is disturbed;
- a proximate electromagnetic relay electrically connected to said sensing switch, said proximate relay comprising an input pole connected in series to an output pole through a solenoid and thence to ground, and further comprising an armature pole electrically connected to a contact pole through an armature when said proximate relay is activated;
- a medial electromagnetic relay electrically connected to said proximate relay, said medial relay comprising an input pole connected in series to an output pole through a solenoid and thence to ground, and further comprising an armature pole electrically connected to a contact pole through an armature when said medial relay is activated;
- a distal electromagnetic relay electrically connected to said medial relay, said distal relay comprising an input pole connected in series to an output pole through a solenoid and thence to ground, and further comprising an armature pole electrically connected to a contact pole through an armature when said distal relay is inactive;
- at least one warning device electrically connected to said medial relay;
- a first circuit comprising said electrical power supply connected in series to the input pole of said proximate relay through said sensing switch when said sensing switch is actuated, the output pole of said proximate relay being electrically grounded such that said proximate relay becomes activated when said sensing switch is actuated;
- said activated proximate relay forming a medial relay circuit comprising said electrical power supply connected to the armature pole of said proximate relay through said arming switch when said arming switch is in an "on" position, said armature pole of said proximate relay being further electrically connected to the contact pole of said proximate relay when said proximate relay is in an activated mode, said contact pole of said proximate relay being further electrically connected in series to the input pole of said medial relay, said input pole of said medial relay being connected in series to the contact pole of said medial relay through said medial solenoid, said output pole of said medial relay being electrically grounded such that when said arming switch is in an "on" position and said proximate relay is activated, said medial relay circuit is grounded and said medial relay activated;
- said activated medial relay forming a locking circuit comprising said electrical power supply connected to the armature pole of said medial relay through said arming switch when said arming switch is in an "on" position, said armature pole of said medial relay being further electrically connected to the contact pole of said medial relay when said medial relay in is an activated mode, said contact pole of said medial relay being electrically connected to said input pole of said medial relay, said input pole of said medial relay being connected in series to the contact pole of said medial relay through said medial solenoid, said contact pole of said medial relay being electrically grounded such that when said medial relay is activated said armature of said medial relay electrically connects said electrical power supply to said input pole of said medial relay grounding said locking circuit such that said medial relay remains activated irrespective of the actuated status of said sensing switch;
- said activated medial relay forming a warning circuit comprising said electrical power supply connected to the armature pole of said medial relay through said arming switch when said arming switch is in an "on" position, said armature pole of said medial relay being further electrically connected to the contact pole of said medial relay when said medial relay in is an activated mode, said contact pole of said medial relay being electrically connected to said warning device and thence to ground such that when said medial relay is activated said armature of said medial relay electrically connects said electrical power supply to said warning device, grounding the warning circuit such that the warning device is powered to an operative mode;
- said activated medial relay forming a distal relay circuit comprising said electrical power supply connected to the armature pole of said medial relay through said arming switch when said arming switch is in an "on" position, said armature pole of said medial relay being further electrically connected to the contact pole of said medial relay when said medial relay in is an activated mode, said contact pole of said medial relay being electrically connected to said input pole of said distal relay, said input pole of said distal relay being further connected in series to the contact pole of said distal relay through said distal solenoid, said contact pole of said distal relay being electrically grounded such that when said medial relay is activated, said armature of said medial relay electrically connects said electrical power supply to said input pole of said distal relay, grounding the distal relay circuit such that the distal relay is activated;
- a third circuit comprising said electrical power supply connected to the armature pole of said distal relay, said armature pole of said distal relay being further electrically connected to the contact pole of said distal relay by the armature of said distal relay, said contact pole being further electrically connected to a critical electrical component of the engine of said tractor such that the critical electrical component is powered to an operative mode when said ignition switch is in an operable mode and said distal relay is not activated, the activation of said distal relay electrically disconnecting said critical electrical component from said electrical power supply.