Can a defense attorney question a victim about a pending case where the victim is the defendant to show the victim has a bias to testify the way he is testifying? Is information pertaining to the victim's pending case "exculpatory"? Can I motion in limine all questioning having to do with victim's pending case on relevancy basis?

As he is a victim, and not merely a witness, it would be irrelevant and you should file the motion in limine. Otherwise, ALL defendants would be permanently impeachable victims of crime. The only caveat is if the crime of which he is accused is related to the crime where he is the victim.

I think you had better be careful. I'm not aware of any cases distinguishing witnesses from complaining witnesses. Read a Supreme Court case styled Davis v Alaska.

I would look at it this way: if the victim's testimony could reasonably be viewed as an attempt by the victim to curry favor with the prosecutor, then you're on thin ice trying to keep it out.

Another hypothetical might be a situation where the defense is arguing that the victim would have an impeachable conviction but for the State's failure to proceed on the victim's criminal charge while the defendant's case was pending trial. Obviously, the argument there would be that it is not fair for the State to hold off convicting someone just so the defense can't use the conviction against them.

I'm sure there are also many cases in which the victim's pending charges would be irrelevant, but I don't think it's a black and white issue.

In order to impeach a witness with evidence of pending criminal charges, "the proponent must establish some causal connection or logical relationship between the pending charges and the witness' potential bias or prejudice for the State." Carpenter v. State, 979 S.W.2d 633, 634 (Tex.Crim.App.1998). The existence of an agreement between the witness and the State is not determinative of the defendant's right to cross-examination. Carroll, 916 S.W.2d at 500.

Quoted from Navarro v. State, 2001 WL 1000712 at *2 (Tex.App.--Corpus Christi 2001 no pet.) (not designated for publication) (no error in excluding pending charges: defense argument that "She obviously has reason to lie, if she's got two pending serious felonies" didn't establish relevance).

Redmond v. State, 30 S.W.3d 692, 697 (Tex.App.-Beaumont 2000, pet. ref'd) (no showing that pending assault charge or pending MTR in DWI were relevant).

David is correct about the Carpenter language that requires a causal connection or nexus between the pending charges and the witness' trial testimony BUT Ben is correct, too, because the language of Davis v. Alaska has been liberally construed. Be aware that, in Carpenter, the pending charges were federal and the conviction on appeal was out of state court. I recently had a case where the witness in question (not the victim) had pending charges from another county, our trial attorney made a great record by firmly stating that the witness had been forewarned that our DAs ofc would not discuss the other county's charges and also that our office had had zero contact with the other county on the pending charges; the witness chimed in with similar statements. I think the fact that a different prosecuting authority is exercising control over the pending cases significantly helps to show a lack of causal connection.