Isuzu Repair: tail light/running light malfunction, voltage drop test, high beams

Question
QUESTION: i have confirmed all lamps and fuses. i changed the light system relay. all lights work except my taillights (1157)and front sidemarkers (194). is this in the switch on my turn signal lever? i have traced the 3 wires. white, red and yellow to a mass connector under the column. the white meters to ground. in the middle switch position the red meters 12VDC. in the headlight position, both meter between .25 to.37 VDC. the instrument cluster light also does not come on. this scenario has occured intermittently over the past year. that led me to think the relay (heat factors under the hood). any suggestions?

ANSWER: So just the taillights do not work or both your running lights and turn signals?

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QUESTION: reverse lights ok
brake lights ok
turn signals ok
hazard flashers ok
headlights & high beams ok

Answer
So if the front markers do not work that could be the hazard and turn signal cansiter(relay) under the dash I believe or it could also be in the wiring somewhere. As for the taillights it could be that the panel is bad on your taillight assembly or the connections are corroded or loose. A voltage drop test on that particular harness will tell you alot as well.