Smiths RVI 2417/00 tachometer

**firthy** · 01-07-2016, 09:44

Hi all hopefully someone on here can help me.
i wish to use the above tacho, let's assume I've got no loom and I'm starting a fresh.
at the moment the only wiring I've got is a live from the battery to the starter solenoid and a wire making my key switch live on number 1. My tach is negative earth and I've got a negative earth battery.

i know red is an earth
what does this require to make it work?
Was told blue Gos to coil? If so what side? - or +
This has been driving me crazy hopefully someone knows

**katana** · 01-07-2016, 10:10

Tach signal always to neg. side of a coil. Most tacho's only have 3 wires ..... +, earth and signal...... so wonder what the 4th is for on yours? Obviously lighting is separate.

**firthy** · 01-07-2016, 21:02

Anyone have an idea?

**katana** · 02-07-2016, 10:13

Just wondering if the red is just a mounting stud? Yellow and blue likely + and signal with orange as earth? See if there is continuity between the red and orange which would indicate that it is earth.

**greengoredstop** · 03-07-2016, 16:30

The stud is B- ground. The orange connector is 12v B+. The yellow and blue are where the white wire from the run position on the ignition switch loops through before going to the B+ connection on the coil. Current from the ignition to the coil is interrupted, which gives the signal to the tachometer. If, after connecting the white wires to their respective terminals, and you do not get a working tachometer, reverse the two connections.

**firthy** · 03-07-2016, 21:36

So is the orange connector a contact feed so could be connected to the wire that comes from starter solenoid that powers my key switch? And yellow is a switched live say from 2 on the key switch?

**firthy** · 03-07-2016, 22:47

Constant not contact

**greengoredstop** · 04-07-2016, 03:27

From the wiring diagram for my 1972 car, the wiring is as follows.

A White/Red wire from the number 1 terminal on the ignition switch to the soleniod. This is the starter activation wire for a car with an inertia starter. For a car with a pre-engaged starter, the White/Red wire goes to a terminal on the starter.

A Brown wire from the solenoid connects to the number 2 terminal of the ignition switch, continuing on to the fuse box.

A Yellow wire from the fuse block to the number 5 terminal on the ignition switch. This connection provides B+ to the radio in the auxiliary position on the ignition switch.

A Green wire from the fuse box to your orange terminal on the tach.

A White wire from the fuse box to the number 3 terminal of the ignition switch, continuing on to the yellow or blue terminals on your tach. The opposite terminal on tach, yellow or blue, has a white wire that goes to the B+ terminal on the coil. The white wire on the number 3 terminal gets its power from the Brown wire, when the ignition switch is in the run position. It also connects B+ to the fuse box, which provides the B+ to the Green wire to the tach when the ignition switch is in the run position, and a host of other wiring circuits.

The points in the distributor, opening and closing, provide the signal to the tach to register the RPM.

The tach is sensitive to the direction of the current flow from the ignition switch to the coil, which may require the reversal of the White wire connections on the tach to record a reading.

Hope this helps.

**firthy** · 04-07-2016, 13:47

Lovely mate that helps a lot thanks will let ya know how i get on. Think my wiring is slightly different but I'll adapt to suit. On my mk1 diagram I've got a brown wire that make key switch live on no 1 and red and white from solenoid to number 3 which activates the starter.

**greengoredstop** · 02-08-2016, 04:19

firthy, got your PM, but could't open it. Hope you got your tach working.

**greengoredstop** · 02-08-2016, 05:30

Got the PM opened, but being a newby, with only 7 posts, it wouldn't let me reply. So, I'll try here

I have RV1's in 2 cars, a 65 Lotus Elan S2 , and a 72 Lotus Elan +2, which I am converting to Zetec power. The tach in the S2 was converted to negative earth about 10 years ago and is still working, amazing. On the +2, I was playing with the wiring yesterday, and was trying to figure out why there were 2 wires to the + side of the coil. It appears the ignition switches are different from the S2 to the +2. So, I cut the harness wrap off and found there was a white/yellow wire from the starter side terminal of the solenoid to the + side of the coil. This wire would be energized when the key is in the start position, providing power to the coil. When the key is released, the power to the coil is through the white wire from the ignition, through the tach, and then to the coil.

Don't ask me if I am going to be able to make the RV1 work with the Electromotive HPV1 lost spark ignition I will be using with the Zetec on Webers. Have used an AutoMeter tach with this ignition with no problems, but with this tach?????? May require new guts. It will be another month before I try stuffing the Zetec into the +2. The chassis mods for the motor mounts are done, along with a new gearbox mount. But, with he engine out, its time to do the mods to the braking system and paint the engine compartment. The DIY aluminum radiator arrived today, so more fab work down the road.

Let me know if the additional wire works.