GMC Repair: Rt Turn signals ano working, turn signal switch, side blinkers

Question
Hi I have a 2000 gmc truck 1/2 ton and the rt side blinkers and flashers are not working. The blinker on the inside is flashing like it should(not fast). I do have a after market plug i that is tappped into the back of the wires for a trailer. They were working before. i have noticed that in the past I had some problems with the trailer lights not working on the rt side also. Then they would work. I checked all the bulbs and am getting no fire at them. Front and rear rt. Do u have any ideas? Thanks you very much in advance for your time. Jimmy

Answer
Hi
Check the large 4 way junction block, under the left side rear, where  the 4 wire harnesses meet.
That junction block is pretty common fault point.
Put the turn signals on, and check for blinking signal on DARK BLUE wire (C1 term. H) coming from front of truck.
If it blinks, check for blink on DARK BLUE wire going to right taillamp assy (C4 term. F). If no blink, the junction block is at fault.
If there is no blink on the C1 term H, check the RT TURN fuse in underhood fuse box.
It should blink, you can testit with a test lamp also.
If it DOES blink and no blink at rear block, you have a broken wire somewhere.
If it DOES NOT blink, I would suspect the multi function/turn signal switch (on steering column).
I Hope this helps.
Good luck
Pawl