Frequently Asked Questions

  • Will my sensors work with my gauges?

    Unfortunately, the short answer is probably not! Whichever company you purchase your gauges from, you will need to use their sensors to match their range. Sensors can vary from range to range even from the same manufacturer. For example the Smiths Classic range sensors will not work with the Smiths Telemetrix range.

    Manufacturers make sensors with characteristics to match their gauges, which may not necessarily match other manufacturers gauges.

    Oil Pressure Gauge – 12v

    Most engines do not have an oil pressure sensor to supply an oil pressure gauge. Vehicles usually have a low oil pressure switch mounted on the side of the engine block. This is a device that illuminates a dashboard mounted warning light, should oil pressure drop below a set pressure. This device has not been designed to make an oil pressure gauge work. If a warning light is required, you will need to fit a t-piece to the engine block, which has a takeoff for the warning light switch and the oil pressure sender.

    T-pieces can be supplied with various threads to suit various engines. Please state make of engine when ordering.

    Oil Pressure Gauge – Mechanical

    The same information applies as above for this type of gauge. In place of an oil pressure sender, you will need to purchase an oil pressure pipe and fitting adaptor.

    Temperature Gauge – 12v

    As stated above, you will need to purchase a matching sender for your temperature gauge.

  • Do my gauges require a voltage stabaliser?

    The only gauges that require a voltage stabaliser are the Smiths (CAI) Classic Range beginning with the part number ‘B’ (‘B’ for Bi-Metal gauge) i.e. BF2202-00.

    Correct Stabaliser Mounting and Connections

    Voltage Stabaliser Connections

  • How do I fit my capillary type temperature gauge?

    This type of instrument is mechanical (part number is prefixed TG of TL) and therefore does not return to zero when the ignition is switched off. The temperature gauge and the temperature sensing bulb are permanently connected by a flexible metal capillary tube. The whole system is liquid filled. DO NOT try to separate the gauge or bulb from the capillary.

    The bulb should be fitted into such a position that it is fully immersed in coolant or oil. The tubing should then be securely cleated to some part of the engine, approximately 3″ – 4″ from the bulb. Bends must not be less than 1″ radius. The tubing should then be run down the engine towards the bulkhead, and be securely cleated every 4″ – 6″. From the last cleated point on the engine to where the tubing passes through the bulkhead, there should be arranged 3 or 4 coils of no less than 2″ diameter from the bulkhead to the gauge. From the bulkhead to the gauge, it is not necessary to insert any more coils unless there is an excess of tubing.

    Diagram of a fitted capillary temperature gauge

    We do not recommend that the gauge is kettle tested or placed in boiling water prior to fitting as this can result in damage to the gauge.

  • Which is best, Ammeter or Voltmeter?

    Ammeters measure electrical current (in Amperes) flowing through a circuit and therefore are wired in series with the load. They are useful when using a dynamo based charging system, as they can warn the driver for example, of negative charging conditions. However, because ammeters are connected in series with the circuit being measured, it requires that current flow (both positive and negative) passes through the ammeter itself. This means that heavy duty cables are required to connect to the ammeter in order to withstand the large electrical current being passed through it.

    If using an alternator based electrical system, the electrical current flow tends to be higher than that of a dynamo, and therefore the greater the current flow the larger the cables need to be. Modern alternators tend to be connected to an ignition warning light that illuminates, should the charging current become too low and thus reducing the need to constantly monitor the charging current. However they are a useful, instant method of measuring current drain incurred from various loads (e.g. headlights).

    Voltmeters measure electrical “pressure” and are connected across a circuit. This means that wiring is very simple and standard automotive wire required for the other gauges can be used. Voltmeters will provide you with the current status of the car battery, as well as indicating charging problems (by a gradual voltage drop indicated on the gauge). In general, if you are concerned about electrical wiring, Speedy Cables would recommend fitting a voltmeter rather than an ammeter.

    How to Connect an Ammeter

    Ammeter Wiring Diagram

    How to Connect a Voltmeter

    Voltmeter Wiring Diagram

  • How do I wire up my tachometer?

    Impulse Tachometers (Universal and Original Equipment)

    The equipment consists of an indicator head and a pulse lead. The pulse lead, when connected in series between the contact breaker terminal on the engine ignition coil and the contact breaker terminal on the distributor, will transmit voltage pulses to the indicator head. There are impulse tachometers to suit various types of engines i.e. 4 cylinder, 6 cylinder, 8 cylinder etc.

    RV Tachometer Conversion

    RVI Tachometer Conversion (Early Type - NEG Earth) Wiring Diagram

    RVI Tachometer Conversion (Early Type - POS Earth) Wiring Diagram
    RVI Tachometer Conversion (Late Type - NEG Earth) Wiring Diagram
    RVI Tachometer Conversion (Late Type - POS Earth) Wiring Diagram
    Three Wire Tachometer Conversion Wiring Diagram
    80mm RVI Tachometer Conversion Wiring Diagram

    The identification code numbers printed on the dials of all Smiths impulse tachometers are prefixed RVI. Universal impulse tachometers can be identified by the 3 terminal block on the rear of the the case and impulse tachometers fitted by the vehicle manufacturers as original equipment, by the single terminal on the rear of the case. The majority of tachometers fitted by the manufacturer are Negative Earth types.

    These are also usually the blocking oscillator types which can be identified by the absence of the pulse loop. Impulse tachometer – check that the iron core and pulse lead assembly is as shown below. The pulse lead should form a symmetrical loop and should not be tight enough to pull the plastic former out of line, as this may well cause a poor electrical connection at the iron core. Poor connection may well result in intermittent operation of the tachometer.

    Tachometer Pulse Loop Diagram

    On some tachometers the pulse loop is somewhat different and mounted inside the instrument case.
    If you have or will fit any type of electronic ignition system or sports coil to your vehicle, you would need to send it to us so that we can convert your RVI tachometer to run with this set-up.

  • What information is required to re-calibrate my speedometer?

    Important Information

    Speedometers cannot just be changed from one vehicle to another. They only read accurately when used on the unmodified vehicle for which they were originally calibrated.
    Even when used on the original vehicle, any changes that may have been made to the wheels, tyres, gearbox or other related parts can seriously affect the speedometers reading to the extent that the vehicle will fail to pass an SVA test or may result in a speeding fine. In this case, the speedometer will need to be re-calibrated.


    To ensure that your speedometer reads accurately when fitted to your particular vehicle, we will need to calculate the required “revolutions per mile”


    For calibration of a new instrument, or re-calibration of an existing instrument, we will need you to provide the following information from your vehicle: 

    1. Take the measurement from the centre of the hub of a drive wheel to the ground (distance measured in inches), with the tyre pumped to normal pressure.
      ANSWER:(1)______________ distance in inches
    2. Put a chalk mark at the bottom of the measured wheel also marking on the ground where it meets. Push the vehicle forward one revolution of the chalk mark and record the distance travelled (measure in inches).
      ANSWER:(2)______________ distance in inches
    3. Now disconnect the speedometer and place a cardboard arrow on the end of the protruding inner speedometer cable.
      Put a chalk mark at the bottom of the measured wheel and then push the car straight forward (with gear in neutral), counting exactly 6 revolutions of the wheel, whilst a partner counts the number of times that the arrow on the cable revolves.
      ANSWER:(3)______________ number of turns of the cable. (N.B. include parts of a turn e.g. seven and a quarter turns)


    Now send us the values that you recorded for Answer(1), Answer(2) and Answer(3) above.

  • What is the requirement for instruments in an IVA test?

    The Individual Vehicle Approval (IVA) test is for any non type approved car, light goods vehicle or motorcycle that has been imported. It is also for any vehicle which is amateur built or contains donor parts from previously registered vehicles. Motor caravans and ambulances can also be tested under the IVA scheme. The tests are currently completed at a number of VOSA testing stations across the country.

    The Vehicle and Operator Services Agency (VOSA) run a number of services to ensure vehicles are safe on the roads. Any vehicle imported, that has not been ‘Type Approved’ or any amateur built vehicles (such as a kit car), has to undergo a pre-registration test before it can be driven in the UK. This is known as an Individual Vehicle Approval test (IVA). It is carried out to ensure vehicles on the road meet UK government safety and environmental standards. The vehicle must be fitted with a speedometer capable of indicating speed in MPH at uniform intervals not exceeding 20mph at all speeds up to the design speed of the vehicle (a 140mph speedometer cannot be fitted to a vehicle capable of 170mph) and must be capable of being read by the driver at all times of the day or night.

    For all true speeds up to the design speed of the vehicle, the true speed shall not exceed the indicated speed i.e. at a true speed of 30mph the speedometer must not show less than 30mph.

    For all true speeds of between 25mph and 70mph (or the design speed if lower), the difference between the indicated speed and the true speed shall not exceed 10% i.e. at a true speed of 40mph the vehicle shall not show more than 44mph.

    The vehicle will be assessed for the associated drive line components for compatibility with the speedometer, such that the accuracy of the device is unlikely to be impaired.

    Instruments must either be recessed into the dash panel or have rounded bezels (not half or full-vee) unless they are behind the steering wheel or within the specified zone exempt area as specified in the IVA regulations.

    N.B. The contents of this page are given as guidance only, for full IVA requirements, you should refer to the IVA Schemes’ own notes on current regulations.

  • How do I connect and calibrate my CAI Stepper Motor Speedometer?

    Speedometers, stepper motor technology, front face programmable part numbers XES3/5-1Bxx-xx (x indicates any character in the part number)

    Caution: Disconnect the Negative battery cable prior to any installation.

    Do I have a stepper motor speedometer or an earlier air core version?

    The earlier air core version speedometers calibration is set via 10 switches located at the rear of the instrument under the grommet.

    The later stepper motor speedometer’s calibration is set via a remote push button assembly supplied with the speedometer or set through the push button, located on the glass/perspex at the front of the instrument.

    Application Notes

    The operating voltage is nominally 12 volts. The range of operation is 10 to 16 volts, negative earth only. The speedometer is intended for panel mounting, it is shower proof from the front only and must be protected from environmental damage at the rear. The speedometer must be calibrated to suit the pulses per mile or km of individual vehicles using the programming harness and push button assembly (supplied in your kit as an accessory) or via the reset button on the front of the instrument. This must be done when the speedometer is installed in the vehicle and powered. The calibration range is from 2,500 to 128,000 pulses per mile.

    Green 1 Switched Ignition positive 12 volt supply, 3 Amp Fuse
    Brown/Slate 2 Connected to harness reset switch OR not used
    Red 3 Pull Up/Down (if required)
    Red/White 4 Instrument illumination 12 volt supply (side light feed)
    Black 5 Chassis or battery Negative
    White/Black 6 Speed signal input (hall ECU)
    Red/Blue 7 Speed signal input for low voltage output senders
    Light Green/Purple 8 Not used

    Setting the pulses per mile

    The calibration mode is selected by switching on the ignition while simultaneously holding the programming button and waiting for 3 seconds.

    After 3 seconds release the reset button, in calibration mode the odometer will flash.

    By momentarily pressing and releasing the rest button each number (extreme left side first) can be incremented to your desired value.

    When the desired value is selected release the button and wait 3 seconds.

    The next number to the right will flash, increment this number in the same way and continue until all the numbers are programmed to your pulses per mile/km.

    At the end of the sequence wait 3 seconds and the speedometer will return to normal operation. If you switch off at any time before the end of the sequence no changes will be programmed.

    For most of the following calculations you will need to know the number of times that your tyre revolves per mile or kilometre. Stand the vehicle on a flat surface and make a mark on the tyre at the closest point to the ground, mark the floor at the same point. Move the vehicle forwards for one revolution of the tyre and measure the distance covered.

    63360 divided by the distance covered in inches = tyre revs per mile

    1000 divided by the distance covered in millimetres = tyre revs per km

    Measure the rolling radius (RR) of wheel and tyre, from centre of hub to ground in inches/mm

    How to calculate the pulses per mile/km (Calibration Number)

    Prop shaft mounted magnetic sensor (magnets or bolt heads moving past the sensor)

    Calibration number = (tyre revs per mile or km) x (differential ratio) x (number of magnets or bolts)

    Sender driven from transmission cable drive

    Calibration number = (cable turns per mile or km) x (number of pulses per sender revolution)

    Calculate RR as above

    Push vehicle forwards on flat ground for 6 tyre revolutions and count the number of cable turns.

    1680 x (cable turns) divided by RR for inches for mm divide by 25.4

  • How do I fit my new CAI TB9***/Kit Fuel Sender?

    Fuel Contents Transmitters

    For uniform section rectangular or circular tanks with 6-hole flange fixing
    (For gauges with bi-metal characteristics, a voltage stabaliser is required)

    TB9010/Kit Top mounted, earth return – “Euro” characteristics
    TB9011/Kit Top mounted, insulated return – “Bi-Metal” characteristics
    TB9012/Kit Top mounted, insulated reutrn – “Euro” characteristics
    TB9013/Kit Side mounted, insulated return – “Bi-Metal” characteristics
    TB9014/Kit Side mounted, insulated return – “Euro” characteristics
    TB9018/Kit Side mounted, earth return – “Euro” characteristics
    TB9006/Kit Top mounted, warning light – “Bi-Metal” characteristics


    Side and End Mounting – Rectangular Tank
    Tank Depth (mm) Arm Length (mm) Tank Depth (mm) Arm Length (mm)
    Bi-Metal Euro Bi-Metal Euro
    610 338 310 432 249 228
    584 325 298 406 236 216
    559 312 286 381 223 205
    533 299 275 356 193
    508 287 263 330 181
    483 274 252 305 170
    457 261 240 279 158


    Side and End Mounting – Cylindrical Tank
    Tank Depth (mm) Arm Length (mm) Tank Depth (mm) Arm Length (mm)
    Bi-Metal Euro Bi-Metal Euro
    610 238 260 381 189 173
    584 272 250 356 179 164
    559 262 240 330 168 154
    533 251 230 305 158 145
    508 241 221 279 147 135
    483 231 212 254 137 126
    457 220 202 229 126
    432 210 193 203
    406 199 183


    Top Mounting – Rectangular Tank
    Tank Depth (mm) Arm Length (mm) Tank Depth (mm) Arm Length (mm)
    Bi-Metal Euro Bi-Metal Euro
    610 542 494 381 316 288
    584 517 471 356 292 266
    559 492 449 330 266 243
    533 466 425 305 241 220
    508 442 403 279 216 197
    483 417 380 254 191 174
    457 391 357 229 165 152
    432 367 334 203 141 128
    406 341 311


    Top Mounting – Cylindrical Tank
    Tank Depth (mm) Arm Length (mm) Tank Depth (mm) Arm Length (mm)
    Bi-Metal Euro Bi-Metal Euro
    610 506 462 381 294 268
    584 482 440 356 271 247
    559 459 418 330 247 225
    533 435 396 305 223 204
    508 412 375 279 199 182
    483 388 354 254 176 161
    457 364 332 229 153 139
    432 341 311 203 129
    406 317 289


    Fuel Sender Technical Diagram

    General Fitting Instructions

    • Measure internal depth/diameter of the fuel tank
    • Select arm length required against tank depth measured, from appropriate table
    • Assemble the wire arms and clips as shown in the diagram to give the specified length
    • Ensure that the float axis is parallel to the tank unit flange
    • Trim excess wire retaining maximum overlap to maintain rigidity
    • Solder at and around the two clips, guard against over-heating
    • Fit the float to the end of the arm, either way round is acceptable
    • Coat both sides of gasket with sealant and assemble tank unit to tank flange
    • Secure firmly and evenly

    NOTE: Interpolation between max and min listed values only is permissible, using the nearest listed value to that measured.

    Fuel Sender Diagram

  • What size hole do I need to cut in the dash for my new Smiths instrument?

    For the 100mm instrument you will need to cut a 98mm diameter hole

    For the 80mm instrument you will need to cut a 80mm diameter hole

    For the 52mm instruments you will need to cut a 52mm diameter hole



    Please note that these hole sizes are for Smiths instruments provided by CAI (Caerbont Automotive Instrument Range) we cannot advise on other makes of instruments.
    You will need to be precise with your measurements and we suggest you measure twice and cut once to ensure you do not have the costly expense of buying a new dash panel.


  • What information do I need to give to make a new speedometer cable?

    Speedy Cables manufacture a wide range of flexible drive cables for speedometers and tachometers for most classic, specialist, commercial, industrial, agricultural and vintage vehicles. We have a range of materials e.g. PVC in heavy and light duty casing, also steel galvanised and brass casing for period vehicles.

    Our skilled technicians manufacture all our cables on site for standard and non standard applications for custom built cars, specialist vehicles and obsolete applications. Where a pattern is not available, please send a detailed drawing of the cable required and we will produce it to the details supplied. Alternatively, we will need to know to what size and make of instrument it is to fit to e.g. 80mm Smiths Classic and to what gearbox it is being fitted to e.g. Ford Type 9 gearbox. We will also need to know the complete length of the cable from tip to tip e.g. 6ft 6″.

    If there are any sharp bends in your cable you may either, have to think of re-routing the cable (minimum radius bend is 6″ see diagram below) or fitting a 90 degree angle drive at the gearbox, this will then make a difference to the cable end fitting so we will need to know if you wish to have this option at the time of your order.

    Fitting New Speedometer Cable

  • Installing and Routing Cables

    Installing and Routing Cables

    Mechanical cables have moving parts, and so they are always subject to wear. That is why they will have to be replaced from time to time. You can dramatically reduce the wear and increase the effective life of a mechanical cable however by following a few simple rules.

    The condition of the flexible drive to a great extent controls the performance of the speedometer or revolution indicator, and poor installation or subsequent damage to the flexible drive will be shown up as an apparent instrument fault. It is, therefore, important that the flexible drive be correctly fitted and properly maintained.

    Smooth Run Securing
    The run of the flexible drive must be smooth. The Minimum bend radius is 6″ with no bend within 2″ of connections Avoid crushing the flexible drive by over-tightening the clip. Flex can be crushed between moving components. Avoid sharp bends as clips, if necessary, alter the position of the clips. Excessive free movement of the flexible drive should be avoided. Fit extra clips if necessary
    Fitting Speedometer Cable Securing the Mechanical Cable
    Connection Connection of inner flex
    Ensure that the threaded end connections are secure with no looseness of the outer casing end collars. Connecting nuts should be tightened by hand. Spanners or pliers whould not be used. It is important that the drive to which the flexible drive connects is free from dirt and grit. Where possible, slightly withdraw the inner flex and connect outer casing first to point of drive. Then slide inner flex into engagement from the other end. It may be necessary to rotate the flex.
    Connecting the Cable Ends Connecting the Inner Flex Cable
    Removal of Inner Flex Checking the Inner Flex
    Most inner flexes can be removedd by disconnecting the instrument end and pulling out the flex. Some must be removed from point of drive end after first taking off C washer at instrument end. The broken inner flex will have to be withdrawn from both ends. Lay the flex straight out on a flat clean surface and roll. Any kinks or obvious signs of damage will be seen. Take an end in each hand, allowing the flex to hang in a loop approximately 9″ diameter and rotate it slowly with the fingers. A satisfactory flex will run smoothly without snatching.
    Removing the Inner Flex Cable Inspecting an Inner Flex Cable
    Lubrication of Replacement Inners
    Apply grease sparingly to replacement flex. Feed flex back into its casing then withdraw approximately 8″ and wipe off surplus grease. Use SHELL SB2628 Grease. Do not use oil
    Lubricating an Inner Cable

Not found your answer? Just ask us!

Above are frequently asked questions. If you do not find what you are looking for or you require more information please call us on 01639 732300 or contact us by email