1999 Yukon Denali Rear Brake and Turn signal on Drivers side Not working

[U2Desire]

As the says I have a 1999 Yukon Denali that the Rear Brake and Turn signal on Drivers side are not working. Also brake light on trailer DOES work but not the turn signal on that side.
I tested the Tail light circuit by plugging it into the passenger side and it works so that rules out that.
Anyone know what wires to test under the dash to test the combo / multi switch?
Also the tail lights or park light do work (both top and middle bulb lights up when the vehicle is running) its just brighter filament does not light up when breaks are pressed or turn signal is on.
Thanks,

U2Desire

[aleekat]

Did you swap the bulb to the passenger side to eliminate a bad bulb?

[U2Desire]

Bulbs are all good. Like I said I plugged the whole tail light circuit into the passenger side to test that and everything works so that rules out the bulbs. I started having the problem or first noticed it when I had to replace the bulbs. I replaced all 3 bulbs 1 (the middle) was blown blown however.
Google searches for this problem tells me it may be the multi-function switch or the tail circuit. Since I ruled out the latter I now need to rule out the switch unless their is a relay or some other circuit that could need to be replaced??? This is my dad's vehicle and he thinks it could be the wiring underneath but I doubt it as the parking lights do work that is both the top and middle bulbs are light up.
I don't know, I just know I need to rule out the switch before messing around with the wiring underneath.

U2Desire

I checked to make sure that when the turn signal is on that it makes the clicking sound which it is so to me that would if I am correct rule out both the multi-function switch and the Flasher module. So looks like we have to look at the wiring underneath for a bad connection.

[aleekat]

I would be looking at where the trailer wiring is spliced into the car's wiring.

[U2Desire]

Must be where the problem is. I also ruled out the Flasher module by switching the 2 modules around it made no difference. Will check out the connections underneath hopefully tomorrow.

U2Desire

[harleyguy]

Originally Posted by aleekat

I would be looking at where the trailer wiring is spliced into the car's wiring.

This is most likely the problem. I have seen and fixed it several times if it's a hack job just splicing trailer wires into truck wiring cut them all and replace with heat shrink connectors. If it's the Correct way with the box that plugs into the lights check connections are clean and external ground is good.

[U2Desire]

Update. So I tested everything on the connector coming from the front (before it spits off to the trailer connector and splits going to the left and right tail light and have no voltage on the Yellow wire which is the turn and brake wire for the drivers side so I am back to it possibly being the combo switch unfortunately I can't find any good info on testing it easily. If I knew what contact and which of the Flasher modules is for that side I should be able to test at that spot to determine if their is voltage coming from the Combo switch.
I would like to be sure that the problem is definitely the combo switch because it is an expensive part to replace. I was hoping that the fact the Flasher is making the flasher sound meant that the combo switch was good but it could be getting just enough voltage to it.
Also I must have been mistaken about the break light on the trailer working on that side. I think I was seeing the tail light lit up.
I have to apologize for any bad grammar in my posts. I have been out of school a long time and typically do very little writing not to mention my grammar wasn't very good before either.


U2Desire