2007 envoy denali tach offroadzj?

Hey there, I've not done an alarm/starter install in years but will be doing one on my 2007 envoy denali tonight. I did a quick google search to see what interesting tidbits I could find and came across this old thread: https://www.the12volt.com/installbay/forum_posts.asp?tid=129535&tpn=1&PN=1 In it offroadzj stated: "Other than the over-rev protection there really is no need for the tach on that vehicle. The drop in acc. tells the bcm to start and the bcm takes over from there. The remote start doesn't actually crank the starter. Did you connect the starter wire?" I was wondering if anyone could expand/clarify that quote. I think what it means is that once you remote start and 12v is applied to the starter wire the bcm sees voltage drop and the starter going so it takes over and starts the engine by cranking the starter as long as needed until the engine is idling (or until it's cranked too long and gives up) so the starter wire is still needed but the tach wire is really not required because the bcm is doing the cranking anyway after a certain point and will not allow the remote starter to over crank or under crank. Any input is appreciated I just want to make sure I understand fully. Thanks, Colin

No, on most vehicles, the accessory wire drops voltage when starting to keep the voltage from dipping to the main engine components when the starter draws power. On some newer GM's, the BCM is designed so that as soon as the key hits the 'start' contact of the ignition switch, it takes over the starting of the vehicle. This is different from most vehicles where you hold the key in the 'start' position until started. On these select GM's, you can just barely turn the key to start then immediately turn it back and it will continue to crank... similarly, you can hold it on crank and once started it will not over-crank. When installing the remote start, the accessory wire will drop voltage. When this happens on those select GM's, the BCM sees it as an indication to start (actual starter wire connection is not even required) and the BCM completely takes over until it is started. With that said, although tach is not 'required' on that car, it still isn't a bad idea to connect it to ensure that the remote start knows the vehicle is truly running, and if something prevented the car from starting, the remote start would re-attempt the start. The tach signal also works as an over-rev protection (on some remote starters) and shuts down if the vehicle starts to over-rev. But in a situation of trying to determine the cause of a remote start failure, you can temporarily leave it disconnected for testing. Hope that helps to clarify everything.Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

Thanks for the detailed explanation!

if you want/need to connect tach wire, there is a tach wire in the large harness under dash that is running from left to right a t the base of to ing molx, it is a white wire, there are a few white wires so you must test, but if i remember correctly it is kinda buried like towards the top rear of that harness or you can go out under hood to a non common injector wire