11 Common Technical Questions
#1 Speedometer Calibration – 16 Pulse
· Where are you getting signal? (SN16, VSS, ECM, MAG. Sensor)
· Are you using SN77?
· What calibration chart are you using? (16000, 32000 or 64000)
· What position are the speedometer dip switches pressed?
· Are you sure power is off to the speedometer when you make a change to the dip switches?
If using SN16, make sure they are using 16000ppm calibration chart and dip switch 5,6,7,8 are OPEN. If they are using a SN77 along with the SN16, make sure they are using 64000ppm calibration chart and dip switch 1,6,7,8 are OPEN.
If they have a VSS signal from any transmission but a Ford, make sure they are using the SN77 with switch 1 ON (2 may also be ON if they are experiencing interference) and have the speedometer set to the 64000ppm default. [Rarely a VSS signal from 700R4 needs to have SN77 switch 1 and 3 ON and speedometer set to 16000ppm default] If they have a Ford transmission, they need the SN77 switch 1 and 3 ON with the speedometer set to the 32000ppm default.
If they have an ECM signal, they need the SN77 set to 1,2,3 ON with the speedometer set to 16000ppm default.
Make sure dip switches are not in opposite direction. Open is pushed down away from the numbers.
Sometimes a dip switch will look like it is pressed in the correct position but it hasn’t “clicked” and is not making contact in the correct direction. Make sure they are all “clicked” in the correct position by toggling every switch once and then setting the default again.
If no change is being seen after they have made dip switch changes, as if power was off when changes were made. Have them check voltage at speedometer with a meter. If they don’t have a meter, have them disconnect power wire from gauge or hot wire from battery to make absolutely sure power is being removed.
#2 Speedometer Calibration – Ultimate Technology
· Is pushbutton connected properly? One wire to ground and one to brown harness wire.
· Are you holding pushbutton until engine is started? Necessary when calibrating speedometer.
· Is speedometer pointer at 30mph or 45mph when doing a marked mile calibration?
Sometimes pushbutton is not connected to a ground. Sometimes pushbutton is defective. Check for continuity through pushbutton (should have continuity only when button is being pressed)
A common mistake is a customer will enter calibration mode to set the speedometer and then start the engine. When this happens, power is cycled and the speedometer is no longer in calibration mode. (it is possible to calibrate the tachometer without engine running) The pushbutton must be pressed until the engine is started (if not a few seconds after). Once the engine is started, the pushbutton can be released.
If the speedometer pointer is pointing at 30mph, no signal is getting through to the speedometer. Check signal. If it is at 45mph and you are NOT moving, it is getting interference from somewhere.
The use of the pushbutton is a common problem. The pushbutton needs to be pushed and HELD for about 4 seconds to enter (or exit) a specific calibration mode (i.e. tach cylinder setup, speedometer marked mile calibration, speedometer real time calibration…) Once in that calibration mode, the pushbutton can be released. To cycle through options, the pushbutton needs to be tapped. A lot of the time the customer will hold the button too long and not be able to cycle through the options (tach at 1, 2, 3, 4 or 8).
It is not necessary to hold the pushbutton while calibrating the speedometer during the marked mile method. The pushbutton can be released after the speedometer pointer moves to the 30mph position (if vehicle is not moving, 45mph if vehicle is moving),
#3 Speedometer Calibration – 8 Pulse
· Where are you getting signal? (SN96, VSS, ECM, MAG. Sensor)
· Are you using SN75?
o Is the model a SGI-5, SGI-5A, SGI-5B or SGI-5C?
· What position are the speedometer dip switches pressed?
o Default should be 2,6,7,8 OPEN
· Are you sure power is off to the speedometer when you make a change to the dip switches?
SN96 signal usually doesn’t require an interface box. Just calibrate according to 8-pulse calibration chart.
A mag sensor signal may or may not require an interface box, depending on how many pulses per mile it is producing. If the signal is less than 6000 or more than 10000 pulses per mile, they will need a SN75. If the signal is
4000-16000ppm, set the SN75 dip switch 4 ON (for SGI-5B/C) or 2 OFF (for
SGI-5 and SGI-5A) and use OUT1. If the signal is more than 16000ppm, set the SN75 dip switch 3 ON (for SGI-5B/C) or 1,2 OFF (for SGI-5 & SGI-5A) and use OUT3.
An ECM signal usually requires a SN75. (some ECM signal are 8000ppm and can be connected directly to speedometer. Check this if all settings on SN75 are correct and cannot get speedo calibrated.) Set the SN75 dip switch 1,2 and 4 ON (for SGI-5B/C) or 1 2 OFF (for SGI-5 and SGI-5A) and use OUT1.
A VSS signal from a Ford transmission (except Tremec) is 8000ppm and most likely doesn’t require a SN75. Any other VSS signal will require a SN75. Set dip switch 3 ON (for SGI-5B/C) or 1,2 OFF (for SGI-5 & SGI-5A). If customer is experiencing interference, have them switch 2 ON (for SGI-5B/C) or upgrade to a new SGI-5C if they have an old SGI-5 or SGI-5A. (a SN79 may also work to filter interference, not sure.)
#4 Speedometer Not Working
· Does speedometer pointer come off stop when power is applied?
o Pointer of 16 pulse and ultimate speedometers should move up with 12V.
· Does odometer work? (if odometer works, signal is probably OK)
· Is speedometer on a 5” speedtachular or “black box” style Bel-era or 1957 Chevy? (possible problem with phone type cables)
· Where is the speedometer signal coming from? (pulse generator, VSS, ECM, mag sensor)
Especially with 5” speedtachulars and “black box” style Belera and 1957 Chevy clusters, customers only wire +12V to one of the two IGN posts on the black box. Make sure power and ground are run to both boards is the box. If odometer is working but not the speedometer pointer, it could mean a bad small phone cable. If speedometer is working but odometer isn’t, it could me a bad large phone cable (which is the same as a computer Ethernet cable)
If signal is coming from VSS, a SN77 or SN75 is required and could be the cause of the speedometer not working.
If a SN77 or SN75 is being used, is the green light next to the dip switches (not available on SGI-5 or SGI-5A) on. If it is not on, then the SN77 or SN75 is not getting power and won’t send a signal to speedometer. If the green light is on but doesn’t blink when the vehicle is moving, the SN77 or SN75 is not getting a signal and they should check the signal source (VSS or ECM). If the SN77 or SN75 green light is blinking and the vehicle is not moving, it could be interference. Try turning switch #2 ON (not available on SGI-5 or SGI-5A) to filter the noise out of the signal.
If SN16 is being used, test by turning shaft with a drill to see if speedometer responds. The signal can be monitored by connecting a multi-meter set to DC volts between the signal post and ground post of the speedometer. With power to the speedometer ON, slowly turn the shaft of the SN16. The voltage should alternate from battery voltage and zero volts. If it does not alternate, then the SN16 is bad.
If a SN96 or SN95 is being used, test by turning shaft with a drill to see if speedometer responds. To test the signal, connect a multi-meter set to AC voltage between the two wires of the pulse generator. Spin the shaft with a drill. The AC voltage should start at zero when the shaft is not spinning and gradually increase the faster the shaft is spun.
Insure the speedometer has a dedicated chassis ground (not touching other ground wires) and a dedicated +12VDC. The power should not be run off the same fuse as high current devices such as radios, AC, electric fans, etc…
#5 Temperature / Oil Pressure Reading Too High
· Where is the sending unit mounted?
· Are you using our sending unit?
· Is there Teflon or some other sealant on the sending unit threads?
· Is the gauge grounded well?
If sender is mounted in the engine head, it will read 15 – 20 degrees higher than actual because of heat from the exhaust. Relocate the sender to the intake manifold if possible. (LS1 engines should have temp sender installed in the head and are not affected by exhaust heat.)
If the gauge has a bad ground, it will make the oil pressure or temperature gauge read high or even peg (if there is no ground).
If the sender has a bad ground (caused by Teflon tape or other sealant), it usually causes a cold reading but in some cases will cause the gauge to read high.
Make sure customer is using one of our senders. It should not be in any bushing (size adapter), which will cause bad readings. Our sender can be identified by the numbers stamped into it near where you would put a wrench to it. The number should be 02025, 02024, 02023 or 02022.
Hot readings can be caused by air pockets in the system. When the vapor in the air pocket passes the sending unit, the temperature will increase higher than the actual coolant temperature. It may be necessary to “burp” the coolant system to remove any air pockets.
Make sure you have the proper coolant level for the cooling system.
#6 Temperature / Oil Pressure Reading Too Low
· Where is temperature sender located?
· Do you have anything other than the gauge connected to the sender?
· Does the sender have any Teflon tape or other sealant on the threads?
· Are you using a Classic Instruments sender?
Teflon tape or other sealants on the threads of the sender will cause a bad ground which increases the resistance to ground and causes the gauge to read lower than actual.
Connecting more than one gauge or electric fan, etc… will cause the gauge to read incorrectly. (hot or cold).
Other manufacturer’s sending units have different ohm ranges than ours. They will not work with our gauge 99% of the time.
#7 Fuel Gauge Not Working / Incorrectly
· Did the fuel gauge come in a set that included a sending unit?
o Sets with included sender are usually SN35 and have a 240-33 ohm gauge.
· What is the ohm range of the fuel sender (if OEM sender being used)?
o GM before 1964 = 0-30
o GM after 1966 = 0-90
o Ford before 1986 = 10-75
o Ford after 1986 = 16-158
o Dodge/Chrysler before 1989 = 75-10
· What is the fuel gauge ohm range? (sticker on the side of gauge indicates what ohm range? If not specified, it is a 240-33)
· Does the pointer move when the gauge is powered?
Make sure the ohm range of the gauge matches the ohm range of the sender.
If the sender doesn’t have a ground or has a bad ground, the gauge will not read accurately. 0-30, 0-90 and 16-168 gauges with the corresponding sender will read Full or high if the sender has a bad ground. 75-10 and 240-33 gauges with corresponding senders will read Empty or low if the sender has a bad ground.
The most common problem with a 240-33 ohm gauge and a SN35 sender is the gauge reading Empty or not reading all the way to full. This is mostly caused by the rubber sending post isolator being pinched between the mounting plate and rheostat support arm. It is necessary for the mounting plate and rheostat support arm to be making good contact with each other in order for the gauge to read accurately. A ground wire should also be run to one of the screws of the mounting plate.
Sometimes the float arm of the sender is not able to move freely inside the tank. Take it out, attach a ground wire to the mounting plate and move the arm manually to make sure the gauge responds as it should. Also, make sure the float arm falls on its own to Empty when you let go of it. (insure it is not sticking)
#8 Erratic Speedometer
· Is the pointer erratic under 10mph variations or over 10mph variations?
· Where is the speed signal coming from? (VSS, ECM or pulse generator)
· What transmission is on the vehicle? (turbo350, 700R4, etc…)
· What speedometer are you using? (8-pulse, 16-pulse, ultimate)
Speedometers with pointer variations of under 10mph are usually caused by the transmission using a speedometer gear. (i.e. turbo350 and 700R4). This may be fixed by a new plastic speedometer gear but most likely will require connecting a SN77 to the signal from the SN16.
Speedometers with pointer variations of over 10mph are usually caused by ignition interference. Usually, shielding the speedometer takes care of this problem.
If the customer is using a SN77, make sure that dip switch #2 is ON. This will also cure an erratic speedometer. This will also cure the problem of a speedometer reading while the vehicle is not moving. (noise on the signal wire caused by the ignition system which only registers when there is no actual speed signal coming from an ECM)
To check if the erratic speedometer problem is caused by ignition noise (requiring shielding) or by the transmission, have the customer get going in the vehicle until the speedometer becomes erratic, then shift into neutral and turn off the engine. Turn the key back on so that the speedometer has power going to it. If the speedometer is steady without the engine running, then the problem probably will be solved by shielding the speedometer. If the speedometer remains erratic without the engine running, the problem is in the transmission and might be solved by using the SN77 to buffer the signal.
Sometimes the SN16 plug will be loose when connected to the sender. This will also cause an erratic reading. This can be fixed by spreading the wire retaining clip on the plug to create a tighter connection between the wire harness plug and the sender.
Ultimate speedometers are sometimes erratic if using an ECM speed signal. This can be fixed by our new SN79 filter. This filter will only work with ECM signals to a speedometer using ultimate technology.
Bad plug wires can cause excessive EMI interference and cause the speedometer to be erratic. Have customer check wires and perhaps use EMI suppressant wires.
Insure the speedometer has a dedicated power and ground.
#9 Speedometer Wiring
· What speedometer signal are you using? (SN96, SN16, VSS or ECM)
· Is your speedometer an 8-pulse, 16-pulse or ultimate?
· Are you using a dedicated ground? (not touching any other ground wires)
· Are you using a dedicated +12V? (accessory of ignition switch or separate fuse on fuse panel)
If using a VSS or ECM signal with an 8-pulse speedometer, a SGI-5C is needed. (Except Ford transmissions, which do not require a SGI-5) The
SGI-5C/B setup is OUT3 dip switch 3 ON for VSS signals. The SGI-5C/B setup for an ECM speed signal is OUT1 with dip switch 1, 2 and 3 ON. SGI-5/A boxes with VSS signals still use OUT3 but have dip switches 1 and 2 OFF and the rest ON. SGI-5/A boxes with ECM signal use OUT1 but have dip switch 3 OFF and the rest ON.
Ultimate technology speedometers using the SN16 pulse generator require the use of the red wire from the speedometer harness. This needs to connect to the red wire from the SN16. Connecting +12V from anywhere else to the red wire of the SN16 might cause the speedometer to read erratically.
Connecting a VSS to an ultimate technology speedometer requires one of the VSS wires to connect to the purple wire from the speedometer and the other to connect at the same spot on ground as the black wire from the speedometer harness. You should NOT connect the other VSS wire to a ground on the transmission or anywhere other than where the speedometer is grounded as this will weaken the signal.
It doesn’t matter which VSS wire goes to the purple speedometer wire (of an ultimate technology speedo) and which goes to the ground as long as the signal is not also connected to an ECM. If the VSS signal is also going to an ECM, where the VSS wires are connected does matter. It will not hurt to connect them the wrong way, it will just make the speedometer not work and the transmission not to shift. If this happens, just reverse the order in which the VSS wires are connected. (this is also valid if connecting the VSS to a SN75 or SN77)
#10 Speedometer Pointer on Wrong Side of Stop
· What speedometer signal is being used? (ECM, VSS, pulse generator)
· What were the circumstances right before the pointer got stuck on the wrong side of the stop?
· Are you experiencing any erratic speedometer movement, especially when the vehicle is stopped?
Speedometer lost power while receiving a speed signal. (i.e. vehicle was moving or was getting false signal caused by interference when power was removed from speedometer)
In order to get the pointer back to zero, a signal of 100MPH must be applied to the speedometer. There are a few methods to accomplish this without actually driving the vehicle at 100MPH.
Method 1 [SN16 signal]:
· Remove pulse generator from transmission.
· Apply power to the speedometer (turn key on).
· Attach a high speed drill or Dremel tool to shaft of pulse generator.
· Slowly spin shaft (direction does not matter) and increase speed until you notice the speedometer pointer move counter-clockwise.
· Stop spinning the shaft of the pulse generator and wait for the speedometer pointer to return to zero.
· Re-connect the pulse generator to the transmission.
Method 2 [Computer (ECM) signal]:
· Switch all speedometer dip switches to the closed position (pushed in on the number side)
· If available, connect ECM tach signal to SN77 speedometer signal interface INPUT. (temporarily remove ECM speed signal from input)
· Start engine and rev motor until speedometer pointer moves counter-clockwise.
· With engine still running, disconnect the ECM tach signal from the SN77 and wait for the speedometer pointer to return to zero.
· Turn off power to the speedometer and set speedometer dip switches back to the previous setting. (also reconnect ECM speed signal to SN77)
· If ECM tach signal is not available, drive vehicle until the speedometer pointer moves counter-clockwise (may require you to be driving 60+ MPH)
· Stop vehicle (do not turn key off) and wait for the speedometer pointer to return to zero.
· Now turn off power to speedometer and set dip switches back to the previous setting.
Method 3 [Built-in Transmission Speed Sensor (VSS)]:
· Switch SN77 speedometer signal interface switch number 3 to the ON position. (you can leave other switches where they were)
· Drive the vehicle slowly until the speedometer pointer moves counter-clockwise (should only take 5-10mph)
· Stop the vehicle and wait for the speedometer pointer to return to zero.
· Switch SN77 speedometer signal interface switch number 3 back OFF.
#11 Tachometer wiring
· What type of ignition system do you have? (HEI, standard points, MSD, ECM Signal, HEMI)
· Can you find the signal?
· Diesel or gas engine?
HEMI engines don’t provide a tach signal. A tachometer pickup from MSD or Autometer is usually required. These tach signal pickups usually output a 1-cylinder signal and will require the SN77 to convert it to a 4-cylinder signal. It may be possible to use a Dakota Digital SGI-8 and connect the input to one of the coils on a multiple coil ignition.
Ram Jet engine computers have analog and digital tachometer signals. Our tachometers require the DIGITAL signal.
Tach filters are not required on our tachometers. They should be removed if any problems are experienced with the tach as they are usually the weak link and go bad.
Diesel applications require a signal from the alternator (if available on the alternator) or from a mag. sensor on the flywheel. If using a flywheel signal, a Dakota Digital DSL-1 is needed to convert the signal. If using an alternator signal, it can be connected to a 3-3/8” tachometer only if it is a 12 Pole signal. If using a 4-5/8” tachometer, the alternator signal may be used if it is a 10, 12 or 20 pole. Otherwise, the Dakota Digital DSL-1 would be needed for the alternator signal as well.
MSD 6AL ignition system has a tach signal output on the side of box. This should connect directly to the tachometer’s signal post. The negative side of the coil will NOT make the tachometer work with this ignition system.