Wiring Diagram Clarification

[DreamsOfA47]

When I purchased my S1 the wiring was shot and the car needed a complete rewire. I purchased the Autosparks harness for an S2 but given that it was for a Renault powered car and that I was completely swapping over the full harness there really hasn't been any issue getting the car wired and running and driving. Now that I'm at the point of swapping in an Autometer tach to replace the fired stock one, I've run into2 points needing clarification. I have been using this wiring diagram to wire the car http://www.lotus-europa.com/manuals/misc/electrical/s2-diagc.gif and it seems to have done the trick. However after looking over the tach instructions https://www.autometer.com/pub/media/manual/2650-1138.pdf I've noticed something and now need clarification: the white wire running from the tach to the coil, and the white-and-black wire running from the coil to the distributor don't have the ignition coil terminals labeled on the diagram. Currently I have white to positive and W&B from negative to the distributor. Is that correct? Or have I wired that backwards?

Secondly, I currently have the original tach out and the white wires with male and female bullet connectors that would normally connect to the tach simply connected to each other to complete the circuit. Of those 2 wires, which is from the ignition switch, the male or female ended wire? The tach I want to install has 2 separate terminals for signal pathway in and out of the gauge and I need to ensure I wire it in correctly.

Edit: It's occurring to me that it may be much simpler to run operate wires with the sole purpose of ensuring the tach is wired correctly. A wire from the fuse box to the gauge and from the gauge to the negative on the coil may be the simplest way to do it...

[jbcollier]

Yup, W to + and WB to -

To use an Autometer tach, you join the white wires (ignition feed to coil), power the tach from a green circuit feed and run a WB back to the coil negative.

[Bryan Boyle]

When I purchased my S1 the wiring was shot and the car needed a complete rewire. I purchased the Autosparks harness for an S2 but given that it was for a Renault powered car and that I was completely swapping over the full harness there really hasn't been any issue getting the car wired and running and driving. Now that I'm at the point of swapping in an Autometer tach to replace the fired stock one, I've run into2 points needing clarification. I have been using this wiring diagram to wire the car http://www.lotus-europa.com/manuals/misc/electrical/s2-diagc.gif and it seems to have done the trick. However after looking over the tach instructions https://www.autometer.com/pub/media/manual/2650-1138.pdf I've noticed something and now need clarification: the white wire running from the tach to the coil, and the white-and-black wire running from the coil to the distributor don't have the ignition coil terminals labeled on the diagram. Currently I have white to positive and W&B from negative to the distributor. Is that correct? Or have I wired that backwards?

You have an S1?  That diagram is for the S2.   There are some (minor, yet important) changes between the two. You are correct; the points switch the negative side of the coil.

Secondly, I currently have the original tach out and the white wires with male and female bullet connectors that would normally connect to the tach simply connected to each other to complete the circuit. Of those 2 wires, which is from the ignition switch, the male or female ended wire? The tach I want to install has 2 separate terminals for signal pathway in and out of the gauge and I need to ensure I wire it in correctly.

Carefully isolating (ie not touching any grounded metal under the dash) the two wires....turn on the ignition, and using your voltmeter, see which one have +12 showing.  I'm thinking (if they designed it properly), the female should be +12 (so the isolation sleeve protects the positive side).

Edit: It's occurring to me that it may be much simpler to run operate wires with the sole purpose of ensuring the tach is wired correctly. A wire from the fuse box to the gauge and from the gauge to the negative on the coil may be the simplest way to do it...

That's what I did when I installed the pertronix distributor; it was just easier to use a spare wire (on my S2, it was the lead from the brake light switch, since I removed the DB10 relay when I put in the euro tail lights with separate blinkers/stop lights, but that probably doesn't apply to your situation.

[DreamsOfA47]

Yup, W to + and WB to -

To use an Autometer tach, you join the white wires (ignition feed to coil), power the tach from a green circuit feed and run a WB back to the coil negative.

So, JB to clarify you're saying run a green wire off of the fusebox to the 12v on the new tach, run a WB from the sig terminal on the tach to the - on the coil, and then a black to a quality ground?

Bryan, yes I have an S1 but the original wiring harness was burned and destroyed so I've swapped in an Autosparks brand S2 harness so everything is wired together as if the car were an S2. When I was needing to acquire the new harness no one had an S1 available so I got what I knew would get the job done. It's taken a little figuring out but it works well! I see your logic and I may test it in the near future, but the change in wiring necessitated by the new Autometer tach may render that irrelevant. Needing new tail light wiring doesn't apply but a new wire does seem to be the easier of all the options!

It doesn't seem that installation should be too difficult but I really don't want to damage this gauge so I need to ensure the wires are correct!!

[jbcollier]

"green wire off of the fusebox to the 12v on the new tach, run a WB from the sig terminal on the tach to the - on the coil, and then a black to a quality ground?"

Green -- power to gauge

Black -- gauge ground

Join the two W wires (or leave them connected depending on the harness) -- this is power to the coil

WB gauge to coil -- coil  negative

[DreamsOfA47]

Thanks for clarifying it with me! I'll hopefully be able to get that sorted in the coming days