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taaron

Tach Signal Powering Ground

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Hey guys, wondering if anyone has run into this problem. I recently started rewiring my car after doing an engine out restoration. Plugging in the old MS 2 3.57 w/ relay board, and all the associated wires. I've found a problem where I was getting voltage on my ground (on the relay board). I was able to narrow it down to the Tach In terminal on the relay board. If I disconnect it, everything grounds right, if I plug it in, I can read 12V at my ground. Anyone have any idea what may be going on here? It does it even when the distributor wire is removed from the distributor. (Also I know the relay board is sacrilege, however I have it and its worked in the past, dont have the funds to upgrade past it at the moment). 

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In case anyone was curious, I solved it by unplugging all my wires and replugging them back in. I also ran the relay board ground to the battery instead of the block. Everything works and the car fired for the first time in a year!

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On 3/25/2019 at 6:18 AM, taaron said:

Hey guys, wondering if anyone has run into this problem. I recently started rewiring my car after doing an engine out restoration. Plugging in the old MS 2 3.57 w/ relay board, and all the associated wires. I've found a problem where I was getting voltage on my ground (on the relay board). I was able to narrow it down to the Tach In terminal on the relay board. If I disconnect it, everything grounds right, if I plug it in, I can read 12V at my ground. Anyone have any idea what may be going on here? It does it even when the distributor wire is removed from the distributor. (Also I know the relay board is sacrilege, however I have it and its worked in the past, dont have the funds to upgrade past it at the moment). 

 

 

So my build I used the relay board and did not wire directly to the DB37 main harness.  However, I actually had to separate the tach wire grounds (pin 1 and 2) from the sensor grounds on pin 17 or 18 cant remember which I used.  Reason being I was getting noise introduced into TPS sensor from the ground of the TACH.  It was so bad that it was always activating my AE. 

 

However, I was using the relay board and from that wiring diagram, the relay board does route them to pin 1-2 but rather with all the sensors (TPS, CLT, IAT), causing issues. 

 

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