Skyrim:Compelling Tribute (Stormcloaks)

Quick Walkthrough
# Find evidence.
# Blackmail Raerek.
# Report to Galmar Stone-Fist.
# Meet the men.
# Take over the caravan.
# Report to Ralof.

Detailed Walkthrough
Blackmail
After reporting to Galmar Stone-Fist, you will be told that Raerek, the steward of Markarth, is secretly a worshipper of Talos and that you will need to find some evidence of this, and then convince him to help the Stormcloaks. Head to Markarth and go into the Understone Keep. Find Raerek's quarters, located to the right as you walk towards the throne. There is a guard there who may or may not talk to you. Don't go up the stairs; instead, take a right and look left. Guards frequently patrol the halls at all hours, however Raerek will be attending to the Jarl throughout most of the day. Sneak in the room, you need to pick the lock, so make sure you have some lockpicks with you. In the dresser against the wall, directly in sight from the doorway, you will find an inscribed amulet of Talos. 

Show the amulet to Raerek and he will tell you to follow him, leading you to his quarters. When you get in his quarters he will immediately start dialogue, assuming you want to extort something from him. Asking him if you could come to some sort of agreement will have him mention a shipment of silver and weapons; selecting any topic except the "All right, it's a deal" one will give you the chance to use speech to gain a leveled amount of gold. After he tells you where the wagon is, he will take his amulet back and you will have to return to Galmar.
 

Ambush
Return to Galmar Stone-Fist at the Reach camp. After telling him that there is a shipment of coin heading to Solitude, he will tell you to meet with some of his scouts that are situated along the road and ambush the wagon. Once you find them, speak with their leader Ralof. He will inform you that the wagon had an accident and is stranded up the road. He will then tell you that he and his men will eliminate the sentry on top of the hill and that you should go in and distract the Imperials so that the Stormcloaks can shoot them. You can also tell them to stay there while you just go in and slaughter.

If you decide to go with Ralof's plan, tell him you're ready and then creep along with him and his men until he stops at a rock. He will then command his men to fire, and they will kill the guard on the ledge and take up positions along it. Now you have to head down to the Imperials. When you approach them, they will pull out their swords and tell you to move along. Simply attack them and Ralof's men will begin shooting the Imperials. Kill all the Imperials and talk to Ralof. That will complete the quest and you will have to head back to Galmar.

Notes
If Season Unending has been completed before starting this quest and Markarth is given to the Stormcloaks, then this quest is skipped and you proceed to A False Front.
The chest on the wagon is locked, but you are free to loot it.
This quest and Compelling Tribute (Imperial) are different radiant versions of the same quest.

Bugs
 
 
 
Using the Unrelenting Force shout on Ralof may work to resolve this.
The horse in the camp may be being treated as an enemy, causing Ralof to be in a combat state. Killing the horse or making it friendly by riding it may solve this.
 
You are able to still do this quest if your bounty is too high. Hopefully if you have already been to the keep, you can fast travel there. Once inside you can kill the guards at the front and then sneak around and hope you aren't found by Faleen, since she can't die. Just reload if she finds you. Once you get to the door, open it and sneak over to the dresser to find the blackmail piece and the rest works like normal. Eventually, the Stormcloaks take over and your Reach bounty disappears.
 Use the console command   to turn off AI detection while talking to Raerek, otherwise wait in his room until he goes there to sleep, and confront him there.

Quest Stages