cogquest Posted July 31, 2015 Report Share Posted July 31, 2015 I think I've searched every forum but im not sure about which wires I need to connect to make my factory tach work with my lt1 swap. I'm pretty sure about the coil wire I should splice into on the lt1 harness (black & white on the grey side of the coil plug) but I don't no which wire on the cluster harness to tap into. I don't have the original engine harness on the car but I do still have the yellow and white connector on the driver firewall. can I run wires from the coil directly to the back of the tach if I remove the tach? can I run a wire from the yellow and white connector to the lt1 coil? can I run a wire from to the coil to to the cluster harness? if so, which wire? thanks for any help. Link to comment Share on other sites More sharing options...
scott87star Posted July 31, 2015 Report Share Posted July 31, 2015 Well you've got a couple issues, first the factory tach is set up to run off the negative terminal of the coil, that sees big voltage spikes whenever a cylinder fires and the factory tach is merely counting those. I know nothing of the LT harness so you'll have to figure out if it is correct. Second, knowing the factory tach is just counting cylinder fires for rpm you can see the bigger problem, if you DID connect it correctly it will be reading twice the actual rpm. The four banger is popping twice per engine revolution, a six would be three per, an eight four, a ten five and a twelve cylinder six. Link to comment Share on other sites More sharing options...
GINASQ Posted July 31, 2015 Report Share Posted July 31, 2015 And a 5cyl? Link to comment Share on other sites More sharing options...
scott87star Posted August 1, 2015 Report Share Posted August 1, 2015 You're on your own, I don't approve of 5 cylinders. Link to comment Share on other sites More sharing options...
wrngwae Posted August 1, 2015 Report Share Posted August 1, 2015 ^LOL Link to comment Share on other sites More sharing options...
cogquest Posted August 1, 2015 Author Report Share Posted August 1, 2015 if I can get it to work I think I can make it read correct, any one have any idea how to hardwire it? can I cut the black and red wires, bypass the circuit board and run them straight to source? again, thanks. Link to comment Share on other sites More sharing options...
ucw458 Posted August 2, 2015 Report Share Posted August 2, 2015 There should be a tach output wire for the LT1 harness. Find that and use this, http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=127/prd127.htm Link to comment Share on other sites More sharing options...
importwarrior Posted August 2, 2015 Report Share Posted August 2, 2015 I wonder if that would work rather then using the MSD setup to convert the signal??? Link to comment Share on other sites More sharing options...
ucw458 Posted August 2, 2015 Report Share Posted August 2, 2015 It might but the MSD tach adapter is cheaper. Link to comment Share on other sites More sharing options...
scott87star Posted August 2, 2015 Report Share Posted August 2, 2015 Cheapest thing is removing the power absorbing resistor from the instrument cluster, or jumpering it said better. Zacman had a write up somewhere on this site. Then you can use any old 0-12V square wave like that out of an MSD box. Link to comment Share on other sites More sharing options...
ucw458 Posted August 3, 2015 Report Share Posted August 3, 2015 Cheapest thing is removing the power absorbing resistor from the instrument cluster, or jumpering it said better. Zacman had a write up somewhere on this site. Then you can use any old 0-12V square wave like that out of an MSD box. Interesting. Does that do away with the small metal box next to the coil too? Link to comment Share on other sites More sharing options...
scott87star Posted August 3, 2015 Report Share Posted August 3, 2015 Yes sir. Just another capcitor. Link to comment Share on other sites More sharing options...
ucw458 Posted August 3, 2015 Report Share Posted August 3, 2015 Good to know. But with my setup you still need those parts. LS2 coils take a 5v trigger signal. That signal may not be enough to run the tach. So my setup uses a MSD tach adapter to convert it to a 12v signal. Link to comment Share on other sites More sharing options...
GINASQ Posted August 6, 2015 Report Share Posted August 6, 2015 You're on your own, I don't approve of 5 cylinders. Lol oh sorry. Link to comment Share on other sites More sharing options...
cogquest Posted August 7, 2015 Author Report Share Posted August 7, 2015 thanks everyone, I wound up finding a old vdo tach I had, removed the guts, transferred the stock tach face and needle to the vdo guts and after a little grinding and drilling got it to fit in the stock location. the 3 wires from the vdo wer pretty straight forward and it works great and looks stock. I didn't think to take pics but ill try to post a vid if any ones interested. Link to comment Share on other sites More sharing options...
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