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Need help wiring my tach

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AHSquarebodySprt

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First off, I have a 1966 Square Body MkIII

here is the wiring diagram i am using:
https://66spridget.blogspot.com/2009/03/i-took-some-time-and-added-color-to.html


Ok now that I have the car running I am troubleshooting the tach.

Where and how do i connect the white loop wire?

In my wiring harness I have a really long white wire (I am assuming this one goes to the tach in a loop somehow (not sure how to wire that) and then goes back to the ignition switch.

Thanks!
 
If the wiring is original, and you have the correct tach, there is a short wire with a male bullet connector on one end, and a female on the other. The harness should have corresponding connectors on two white wires. It's that simple, but without photos of what you actually have in front of you, I can't offer any more than that.
 
In addition to the white wires you will of course need to connect power and an earth ground to the tach. The earth ground is typically made either to a male spade lug spot welded to the gauge case or with ring terminal attached to the mounting studs on the back of the gauge. The 12V power supply is typically a green wire that attaches to a male spade lug attached to an insulator plate on the back of the gauge. Lastly there is gauge illumination which you need to tie into the lighting for the other gauges.

As Gerard said, this all depends on which tach you have. Pictures are helpful.
 
dklawson said:
In addition to the white wires you will of course need to connect power and an earth ground to the tach. The earth ground is typically made either to a male spade lug spot welded to the gauge case or with ring terminal attached to the mounting studs on the back of the gauge. The 12V power supply is typically a green wire that attaches to a male spade lug attached to an insulator plate on the back of the gauge. Lastly there is gauge illumination which you need to tie into the lighting for the other gauges.

As Gerard said, this all depends on which tach you have. Pictures are helpful.
Click to expand...


It looks just like this one:
https://www.ebay.com/itm/Used-elect...ash=item28174d17d7:g:tIsAAOSwKfVXJl0O&vxp=mtr

My grounds are all ring terminals like this:
https://www.cycleterminal.com/Proper-battery-ring-terminal-crimp.jpg

Where is the best place to attach all of these grounds on each gauge?

I only have one white wire that has a female connection to connect to a post (male) terminal. So do i just simply loop that around that post where the current one is? How the heck does that work?
 
With the RVI tach you should have a little plastic block with two holes in it that the loop goes through. Over that is a metal bridge and the assembly gets attached to a post with a small knurled nut on it. Don't know if that is what you need to know or not. The RVI in original form must have a positive ground electrical system to work. In general the RVI is a can of worms. My RVI on my midget was working perfectly till this spring. It now vary's according to the pressure I put on the loop when I reach under the dash.

Kurt.
 
nomad said:
With the RVI tach you should have a little plastic block with two holes in it that the loop goes through. Over that is a metal bridge and the assembly gets attached to a post with a small knurled nut on it. Don't know if that is what you need to know or not. The RVI in original form must have a positive ground electrical system to work. In general the RVI is a can of worms. My RVI on my midget was working perfectly till this spring. It now vary's according to the pressure I put on the loop when I reach under the dash.

Kurt.
Click to expand...

All i have is the small metal post with that nut on it. I don't have a plastic block with any holes in it.

I have the car wired to positive ground.
 
For the record, RVI tachs do not have to be positive ground. There are both positive and negative ground versions. In general, the gauge face will tell you what the ground of the gauge needs to be... however, you can convert them and most people don't update the gauge face or make notes on the gauge to tell you its ground has been changed.

RVI tachs are sometimes called impulse tachs. They work by sensing the pulse in current flowing to/through the ignition coil. The plastic block with the loop of wire in it creates a weak magnetic pulse that is sensed by a pickup inside the gauge. You will need the plastic block and metal bridge that Nomad mentioned for the gauge to work.

Is the engine running now? If so, the easiest method for you to deal with the white loop of wire is to extend both ends of the white wire loop, passing the extension wires through the firewall and routing them to the ignition coil and distributor. Remove the white/black wire that is running between the coil and distributor. Connect one extension white wire to the coil and the other to the distributor where the white/black used to be. That will allow the coil current to flow through the white wire loop. The wiring won't look original but it will allow the tach to work.

If you don't want to run extension wires to the coil and distributor... post back and ask. There is a more "factory" way of doing this but you have to sort out the wires behind the dash.

The insulated spade terminal on the back of the gauge gets a green wire (switched, fused) feed from just about any circuit you want to tap into. The ring terminal wires simply get their other end connected to the car's chassis somewhere convenient behind the dash.
 
Last edited:
If you have the original wiring it very likely the plastic block stayed on the removed wire. Not hard to overlook.

BTW I'm running an RVI that I converted to negative ground....not hard to do.

Kurt.
 
nomad said:
If you have the original wiring it very likely the plastic block stayed on the removed wire. Not hard to overlook.

BTW I'm running an RVI that I converted to negative ground....not hard to do.

Kurt.
Click to expand...

Probably should have checked there first.

The original wiring was covered in tar as the previous owner of this car thought that would be a good way to stop leaks.....

:chargrined:
 
nomad said:
If you have the original wiring it very likely the plastic block stayed on the removed wire. Not hard to overlook.

BTW I'm running an RVI that I converted to negative ground....not hard to do.

Kurt.
Click to expand...


You were right! Everything was still on the original wiring. Glad i kept it in a garbage bag in the corner of my garage for a decade!
 
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