Medium and Heavy Trucks
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Hi Ryan, My name is***** will be glad to try to help. Diagrams for the 1987 models are tougher to come by as all of them are on the older systems in the archives now. What you will want to do is test for power on both sides of all fuses with a test light with the key switch on. Replace any fuses with power only on one side. For your relays you will swap them one at a time with a known good one for test purposes. Once confirmed okay you will test for power in and out of the multifunction turn signal switch for a possible failed switch which is most common if all the wiring checks out okay to the light assemblies, and you have confirmed all bulbs, grounds, etc. are good. Let me know
Also check the wiring in the dash and test your switches and connections at the switches for damaged connector pins.