St165, gen4 swap, trying to get tach to work

760gt4

New member
So I have a gen4 3s in my st165 and I'm trying to get my tach to work. Since the motor uses an ecu based tach I need to change or bypass the resistor but I'm not sure on which resistor it might be since the circuit board looks different than in the sw20 so I can't use it as a comparison My guess is this one in the picture but can anyone clarify? Or maybe one in the other picture?
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760gt4

New member
OK, that circuit board looks exactly like the one on my tach as well. So did it work perfectly fine after you put the 30k resistor?
 
Welllll I was not sure what my solution was going to be yet and I have a tac converter box so I left those wires unhooked. I did not have my computer with the diagrams to figure it out so I am not sure yet I will have to get back to you in a couple days. Also Charlie said you can remove and replace the resistor with a 15k one. I bought 2 15K and 2 30K just incase. They are super cheap at Digikey like 10 cents or something. I paralleled the 30k one on like he did I will see how that works tomorrow or Monday. I can get you the part numbers if you need let me know.
 

760gt4

New member
I dont have time today to try it out or else I would, and tomorrow morning I leave to Alaska for work. I'll be home in about a month so I'll have to wait til then to try it out. I've had 3 msd tach converters and they all worked perfectly for 5 minutes before randomly burning out so I gave up on those.
 
It worked! Unfortunately I hear a little knock in the bottom end now... looks like its coming out for new bearings and maybe replace the crank. But hey the tachometer works great! lol 1 step forward 2 steps back.
 

760gt4

New member
Did you happen to get a picture after you paralleled the resistors? And sucks to hear about that knock hopefully you get everything sorted out.
 
No I didn't but there is a pic on that thread I linked you to earlier of what it should look like. Mine is a little sloppier, I am not very good with a soldering iron I usually use a small torch for soldering wires. It is a fiddly job for sure, take your time and stay calm. lol
 

760gt4

New member
I just saw it again and now I understand it. I'll do that as soon as I get home which should be in a month or so. I will get the tach working and as soon as I do I will remove the current setup and transfer it to my new st165. Here's the picture of the 30k resister paralleled to the original for reference.
 

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