2008 buick lacrosse v6 3.6l. Changed battery now won't start. Starter won't turn over no click from selenoid.. Have been messing with this for a while. Bypassed the crank relay. When I use a jumper wire to short across where the relay was plugged in the car will turn over. If I turn the key to start position when doing this the car will start and run fine. Also when the car starts tachometer speedometer fuel gauge temp gauge etc do not work.

Are you sure you got ALL connectors reconnected? Maybe one fell down somewhere.

Is there a 'security' or 'anti-theft' indicator on the dash? If so, what is it doing when you try to start?
This may not be the issue, given that it starts up, but it'* worth checking.

Also, step back to the basics. Check all cables for tightness at both ends, and for corrosion.

Well for one thing, this not your grand dad'* starting system.......two relays and the BCM and ignition switch are also involved...

First, you should check for B and P codes...for example, a bad hood ajar switch can set a code, and prevent a remote start, not sure if it prevents a manual start....

Since you removed the crank relay, and jumpered it and the car cranked over, this means either the relay is bad, you are not getting power from the Ign 1 relay, or the BCM is not grounding the crank relay......

A high end scan tool makes diagnosis easier, but not everyone has one, including moi....

So first try swapping out the crank relay......then make sure you have power from the Ign 1 relay.....then you check for a wiring problem between the BCM and the crank relay....if ok, then you check the input from the ignition switch to the BCM...if ok, you need a BCM....

I'm 99% sure it will manual-with-key-in-ignition start with the hood open. The other 1% is me not sure if GM did something odd in the early days of remote-startable cars and I just haven't stumbled across it. I've messed with GM cars from all around then (and later) and they all key-started with hood open.

Primary issue with a hood switch signaling <hood-open> is no remote start and on most of them no anti-theft, just doors locked and two toots of the horn if you press lock on the fob again. The two toots appear to intend to advise: "I have a problem locking your car completely but the doors are mechanically locked so you can continue into the mall/soccer game/movie with theft of your vehicle and contents less likely than otherwise" .

Cathedral, I wan't sure if a code was set by the switch if it would start.....but you are right, should be able to start the car with hood open....

All he did was replace a battery....two cables.....nothing to miss as far as reconnecting them....

Only thing I can think of, did he have the key in the ignition, and in the "on" position, and when he completed the circuit with the second cable, did he send a surge through there that may have affected a circuit in the BCM?

Yeah, I was thinking weird stuff like that too. If he bypasses a relay and it starts, while newly having no gauges working, I'd have to lean towards something causing multiples to burn out etc.

Hey alankennedyl , probably a good idea to check your fuses too. All of them.