told/would tell

Re: told/would tell
This is just my opinion...

"I wish you told the truth" suggests (to me) that the speaker is wishing that the listener would tell the truth more often than he or she habitually does.

"I wish you would tell the truth." suggests that the speaker has just heard what he or she knows to be a lie from the listener, and is requesting the listener to tell the truth in the immediate situation.

I prefer the 2nd one. "I wish you told the truth" could be referring to a specific event in the past where that person lied. "I wish you would tell the truth" seems more like an ongoing/current thing.

"I wish you told the truth" to me also seems more blunt/mean.

But it also depends on the context.

If the lying had taken place in the past, IMO, the sentence should be "I wish you had told the truth."

You are correct. If the sentence were referring to a specific action in the past (one that happened before another action, such as the telling of a lie), it should be put in the past perfect tense. To my ear, "I wish you told the truth" is more suited for general or habitual actions: "You always lie. I wish you told the truth."