Light Problems - Freightliner fld120 wiring

ok guys i have a 97 freightliner fld120 and its a dump truck.. the truck has sit for about 1/2 mths with alot of rain..now when i parked the truck all the lights was working fine with no problems.... now i start to use the truck more i have light problems....i have 2 lights on each side 1 on the top and 1 on the bottom, the both have there own wires from the terminal block....so i start to use the truck and the bottom light will not work when brake is applied, but all other lights work.....i take the light out and put a new light in and the top light stop working.....long story short i go through all the wires and all is well(been working since i got the truck 5 years ago) take all the wires off and clean the terminals sand and oil and now the rev. lights come on when i touch the brakes... i think its a relay problem but not sure.. what do you guys think i need to do??? i worked on this thing all day today with a volt. meter( i use to be a forman at the power comp. ) but dont know everything... i think some water has go into the relay panel or something like that since all was good when parked and the problem seems to move when checked.. please help me and give what you think....thanks mike

 

ther is a box at the back of my truck ..fleetspec on the top that all the wires run to..it has 6/7 bolts in it that conn. all the wires, rev,stop,turn,and park ...i took all of them of and sanded them clean and spayed them with pb blast thats when they started to act really funny.. went from the pass side brake light at the bottom not working to the rev. lights coming on when brake is pressed, now press brakes and no bottom light and all the others work...they get go from low to bright some times and i thought ground but found nothing...at the back.. took the plug loose from the front(the main 4 wires) and still nothing.. i guess i will have to oam all of them out from the front to the back and see if there is anything broken or rusted...man this is killing me truck sit with no work now i have work and worried about the dot ...where does it end???? lol mike

 

thanks guys i will give the test lighta try and clean the p b off as well..i gotta fix this as i dont need a ticket..

 

i think dave is on to something about the ground...i took all the wires loose and cleaned them again,put them all back and now the rev. light comes on when i press the brake..got cold outside and had to give up for he night and then it snowed here last night...so i will keep at it and fine it soon i hope...also i just use the volt. meter to see if i was getting volt. to the wires..but i am going to pick up a test light to use on the box,and inside the trucks relay panel...thanks mike

 

ok guys still not working...i took the day and checked everything i could think of...i took ever 1 of the relays out clean and greased the ends,i took all the wires out and brushed them...what is getting me is that i have 2 lights on each side 1 up top and 1 down low...now the 1 up top works ,and if i change the bottom light out the top will stop working....i have leds up to and the normal round lights at the bottom..leds have been in the truck over a year so i dont think that has anything to do with it...i pulled the wire harness from the back all the way to the front under the truck and then found it up to so i could follow it inside the truck...the harness has some green corrosion on them so i brushed and clean them and blow them out with air, then i put in a little grease (electrical grease with a grit in it) ...am i missing something here??? anybody have any suggestion as to what i may need to try ????i am at a loss now and just starting to get back to work (dump truck) this is killing me....i used a test light to verify that i had volt. at all points...thanks mike

 

well guys i think i have found the problem...i checked every wire i could and relay that i could,then i started to mess with the turn signal switch that the brake lights also go through and that s my problem.. the turn signal switch is bad...now i feel stupid lol..but anyway i took the switch out the truck took it apart and cleaned it out full of dirt and junk, reinstalled it and all the lights work with no problem..i did call the dealership and order me a new switch cause i think this 1 is the orig. for the truck 97..so there you have it the turn signal switch was is the problem...i did learn alot working on it and alot about wiring....thanks for all the help and ideas guys..hope this helps somebody else down the road.. cause i would never thought that the switch would control the brake lights as well..going by the diagram they run right into the switch and i found the wire(they are all #ed) that run the brake lights, thats what mad me remove it and check it out...mike