Never tried it, but basically it wires the tach in parallel instead of series. Strange.
Here's the link-
Bypassing a Bad Tachometer - 1969 / 1970 Mustang
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Here's the link-
Bypassing a Bad Tachometer - 1969 / 1970 Mustang
1970 Tach Bypass – Flawed Schematic?
How many of you have seen this site below (also see my pictures) that proposes a bypass circuit for the 1970 Mustang tachometer?
http://1970mgr.org/_TachBypass.htm
Are there many auto electricians on this forum? Take a look at his bypass and tell me if it makes any sense to you. From my perspective, something is seriously flawed with this tach bypass circuit. Just use some common sense here: If you install that add-on trailer connecter pair that has a direct shunt between the power source and the outgoing (after the tach) line to the coil, you have effectively bypassed the tach itself. Why would any current then need to travel thru the tach with this shunt in place, not to mention it being curtailed at the very least? … which would alter your normal tach indication for sure!<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com<img src=" /><o
></o>
Remember that the 1970 tach is a Faria (FoMoCo) “series” type tachometer that is wired in series to the ignition coil. This bypass wire turns it into a parallel circuit which means it’s not all going to flow thru the tachometer anymore. For a bypass to be truly useful, this bypass shunt line would have to incorporate a switch so that it could remain off during normal operations and only be turned on (connected) if the tach had failed and the ignition cut off. I believe once this line is connected (switch on), the tach will no longer read correctly, probably abnormally low (due to a lack of normal current flow).<o></o>
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His statement: “<I>Connector 2 is wired to allow the tach to function and to receive power from a separate ignition source” </I>doesn’t make any sense to me because the factory tach can not normally operate in a parallel configuration.<o></o>
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Perhaps I’m not seeing something here, but before I wire up my car’s tach, I wanted to have some other opinions on this. Any input would be appreciated.<o></o>
http://1970mgr.org/_TachBypass.htm
Are there many auto electricians on this forum? Take a look at his bypass and tell me if it makes any sense to you. From my perspective, something is seriously flawed with this tach bypass circuit. Just use some common sense here: If you install that add-on trailer connecter pair that has a direct shunt between the power source and the outgoing (after the tach) line to the coil, you have effectively bypassed the tach itself. Why would any current then need to travel thru the tach with this shunt in place, not to mention it being curtailed at the very least? … which would alter your normal tach indication for sure!<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com<img src=" /><o
></o>Remember that the 1970 tach is a Faria (FoMoCo) “series” type tachometer that is wired in series to the ignition coil. This bypass wire turns it into a parallel circuit which means it’s not all going to flow thru the tachometer anymore. For a bypass to be truly useful, this bypass shunt line would have to incorporate a switch so that it could remain off during normal operations and only be turned on (connected) if the tach had failed and the ignition cut off. I believe once this line is connected (switch on), the tach will no longer read correctly, probably abnormally low (due to a lack of normal current flow).<o
></o><o
></o>His statement: “<I>Connector 2 is wired to allow the tach to function and to receive power from a separate ignition source” </I>doesn’t make any sense to me because the factory tach can not normally operate in a parallel configuration.<o
></o><o
></o>Perhaps I’m not seeing something here, but before I wire up my car’s tach, I wanted to have some other opinions on this. Any input would be appreciated.<o
></o>Attachments
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No, the tach is still wired in series, but the circuit it's located in is parallel to another circuit.Never tried it, but basically it wires the tach in parallel instead of series. Strange.
Here's the link-
Bypassing a Bad Tachometer - 1969 / 1970 Mustang
![]()
Let me see if I understand you correctly. I have 3 examples of a motor connected in series (like the factory tach is). The second one has a "bypass" in its power feed (like his diagram shows). Are you telling me that the motor will not spin slower with the bypass installed? What about in my last depiction?
Only in the 1st case does all the current go thru the motor. In the next two cases there is an easier alternate path for current flow and thus the motor's rpms (or tach reading) would be deminished giving way partially to this easier pathway.
Am I just not seeing something here? I'm not trying to be obstinate - just trying to learn here.
Only in the 1st case does all the current go thru the motor. In the next two cases there is an easier alternate path for current flow and thus the motor's rpms (or tach reading) would be deminished giving way partially to this easier pathway.
Am I just not seeing something here? I'm not trying to be obstinate - just trying to learn here.
Attachments
1 - 14 of 14 Posts
