[ 0017 ] fig1 illustrates in perspective a truck 10 comprising a combination of a tractor 12 and a trailer 14 . tractor 12 includes the conventional major systems of a vehicle , including an engine , a starter system for the engine , brakes , a transmission and identification lights . tractor 12 and trailer 14 mount several exterior lamps by which the vehicle provides light for its driver to see by and means to be seen , particularly at night , by others . on the front of tractor 12 are headlights 16 , front corner turn signal lamps 17 , and fog lamps 18 . several identification lights 21 are installed on the roof of tractor 12 . a lamp box 19 installed on the rear end of tractor 12 carries additional turn signal lights , reverse lights and brake lights . as is common , the forward and tail end turn signal lights have a hazard function and can be cycled on and off together ( generally the forward pair together and then the tail end pair together ) to provide warning to passing motorists . a pair of electrically activated horns 22 are installed on the roof of tractor 12 . trailer 14 also carries various lights , including tail end brake and turn signal lamps ( not shown ), as well as identification lights 23 which may be positioned any where on the trailer , but are commonly found on upper and lower edges of the trailer . operation of all lamps in all of their possible operational modes is best verified by visual inspection of the lamps in operation . referring now to fig2 tractor 12 includes a network 11 based on an electrical system controller ( esc ) 30 and including a shielded twisted pair bus 60 over which data communications between esc 30 and other controllers occur . an electronic gauge controller 40 and esc 30 are of primary interest to the invention . among other vocational controllers and sensor interface modules which may be connected to bus 60 are an automatic transmission controller 50 , an engine controller 20 and an antilock brake system 120 . collectively , bus 60 and the various nodes attached thereto form a controller area network ( can ). active vehicle components are typically controlled by one of a group of autonomous , vocational controllers . however , most lamps are powered directly from esc 30 , which includes a number of power field effect transistors ( fets ) for that purpose . a switch set 42 for the lamps is attached to egc 40 , which communicates requests to esc 30 over bus 60 . less usually , switches 32 may be directly connected to esc 30 to provide the same control . a panel display including a plurality of warning leds 44 is connected to and under the control of egc 40 . esc 30 additionally drives horn transducers 36 mounted in the horns 22 on top of tractor 12 . esc 30 includes a programmable computer including conventional memory ( both volatile and non - volatile ) and program execution capacities ( cpu 31 , see fig3 ). [ 0020 ] fig3 is a high level circuit schematic of egc 40 , esc 30 , and a plurality of lamps energized under the control of the esc as configured for a preferred embodiment of the invention . esc 30 is a programmable body systems computer used to control many vehicle electrical system functions . in the past , many of these functions were controlled by switches , relays and other independently wired and powered devices . esc 30 is based on a microprocessor 31 which executes programs and which controls switching of a plurality of power fets used to actuate vehicle exterior lights and the horn . egc 40 communicates with esc 30 over an sae j1939 data link ( bus 60 ) and can controllers 43 and 143 . egc 40 is based on a microprocessor 41 but includes only limited and typically fixed programming . egc 40 handles switch 45 inputs providing manual control over headlights and enablement of the headlights 16 . another source of switch inputs may by provided by a switch pack 38 which is connected to microprocessor over an sae j1708 bus and controller 39 or through switches associated with brake pedals , turn signal levers and other similar systems . activation of a lamp test routine begins with movement of the ignition to the “ on ” position , detected by microprocessor 41 of egc 40 , and with an arbitrary sequence of inputs from other switches connected to microprocessor 31 , including a set of cruise control switches in a voltage divider network 220 , park brake set switch 140 and horn switch 138 . a sequence of actuation of these switches trigger the lamp test cycle . alternatively , a switch mounted in switch pack 38 may be used to start the lamp test cycle . a preferred trigger sequence of switches is to move the ignition key to the start position , set the parking brake and then simultaneously press cruise on and cruise resume switches followed by depressing the horn button . cancellation of the cycle comes on a time out condition , or by meeting any number of other conditions , such as moving the ignition to the “ off ” position , tapping the brakes , turning on the headlights , etc . some of these signals , such as the brake signal may be communicated from esc 30 . microprocessor 31 can apply activation signals to all of the lamps subject to inspection as well as to a horn coil 36 . in the case of headlights 16 , this may also involve pulling high a headlight enable line by instruction to egc 40 . microprocessor 31 is connected to provide an activation signal to a horn power fet 51 which in turn drives a horn coil 36 . another signal line from microprocessor 31 is connected to drive a park light fet 52 which in turn drives park / tail / marker light bulbs 37 , a license plate id and mirror light bulbs 38 . yet another signal line from microprocessor 31 drives a low beam fet 53 , which in turn drives filaments in headlight bulbs 41 and 48 . low beam fet 53 and park light fet 52 further require an input on the headlight enable line to operate . still another pin on microprocessor 31 controls a high beam fet 54 which drives high beam filaments in bulbs 41 and 42 . lastly , a set of four pins on microprocessor 31 are used to control the turn signal lights at each corner of the vehicle . four fets 55 , 56 , 57 and 58 are connected to receive the signals and , in turn , to power bulbs 43 , 44 , 45 , and 46 mounted in turn signal fixtures at the four corners of the vehicle . fets 55 , 56 , 57 and 58 can be activated together or separately to provide turn indications and emergency flasher operation . [ 0023 ] fig4 is a high level flow chart which illustrates the testing cycle for the lamps and drive circuitry beginning with turning the ignition on and setting the park brake ( step 90 ). if the test conditions are not met at step 91 the cycle is never initiated ( end step 92 ). however , if the cruise control on and resume buttons are simultaneously hit and the horn activated as determined at step 91 , the testing cycle begins with activating output fets for the marker lights and work light ( if so equipped ) for two seconds ( step 93 ). then , the fets for the marker lights are left on , the fet for the brake lights is activated for two seconds and the work light turned off ( step 94 ). next , at step 95 , the fet for the marker lights are left on , the brake lights turned off , the left turn signal is cycled on and off , the low beams , the work light and fog lamps are activated for two seconds . next , at step 96 , the left turn signal is canceled , the work light turned off and the right turn signal is turned on . the high beams are turned on . at step 97 all of the lights on at step 96 are turned off and the four bulbs constituting the corner turn lights are flashed in unison ( or front to back ) to test flasher operation . the work light is turn on again . finally , at step 98 all of the lights are turned off and the horn is sounded . next , at step 99 it is checked to determine if the operator has canceled the operation of the test system . this step can occur after each functional step . if operation has not been canceled it may be determined if the process has timed out ( step 101 ). following the yes branch from either of steps 99 or 101 cancels the procedure . the no branch restarts the cycle . the test loops , causing each set of power fets to be repeated in the same sequence until cancellation . while in theory the sequence could be varied , a fixed sequence is simpler to implement and use . the time out period is preferably set to about five minutes to provide ample time for the user the view the entire vehicle . the present invention enables a vehicle operator to perform a light check of a vehicle with the assistance of a second person . this in turn saves both time and helps insure completeness of the inspection . the test feature can also be used during vehicle manufacture to ensure that electrical connections to exterior bulbs have been correctly made . while the invention is shown in only one of its forms , it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention .