Thanks camp freddy and dklawson your are most helpfull apart from your conflicting opinions of what goes to 'NO' 1.
Is it a 12v supply or earth? What will happen if i put a supply and it needs a earth, will it damage the gauge?
Wiring In A Rev Counter
Started by
Doodling
, Aug 10 2009 04:43 PM
18 replies to this topic
#17
dklawson
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Moved Into The Garage
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Posted 12 August 2009 - 12:26 PM
I didn't realize that our comments conflicted.
I'm on page 2 of this thread and can no longer see your picture so I have to do this by description, not numbers. The spade lug on the piece of brown circuit board is "hot". It receives switched 12V. Most of the green wires on Lucas wiring schemes are switched, fused 12V.
The two bullet connectors are the ends of a loop of wire inside the tachometer. I'm going to try and NOT confuse you but this can be complicated so read through the following two paragraphs a couple of times.
On factory installations of this tach, one of the bullet connectors is attached via a white wire to a switched terminal on the ignition switch, the other bullet connector is connected via a white wire to coil (+). Thus... anytime you turn on the ignition (and the points are closed), power to the coil flows through the loop of wire inside the tachometer. When the points open and close, the tach's internal induction loop makes a magnetic pulse that the gauge uses for its input signal.
On aftermarket installations of this type of tach, the general rule is that you pull two (2) white wires from the passenger compartment. One goes to the coil, the other to the distributor. You disconnect BOTH ends of the white/black wire going between the coil (-) terminal and the distributor. (Please note that is coil (-), NOT coil (+)). The ONLY reason this is done on aftermarket installations is that the gauge manufacturer is trying to spare you having to pull apart your ignition switch wiring. Functionally, the two wiring schemes are the same. When the points are closed, power flows through the induction loop inside the tach. Regardless, one bullet is connected to coil (-), the other to the distributor terminal where the white/black wire was before.
Were I you, I would follow the second wiring method I proposed. Pull two wires to the distributor and coil. If you notice strange behavior on the tachometer, switch the connection points of the two white wires (i.e. Move the wire connected to the coil to the distributor and vise versa). This only reverses the direction the current is flowing in the induction loop. If switching the white wires helps... great. If it doesn't, and the engine runs OK, all you can do is check your earth and power connections. If no wiring problems are found, the problem lies in the gauge.
Before closing let me offer an observation. The RVI tachs have been out of production since the mid-1970s. The gauge you have is likely 35+ years old. It simply may not work any more or it may be too "tired" to read accurately. There is a mylar or polyester capacitor inside the RVI tachs that fails over time. There are also one or two germanium transistors inside the tach (quantity dependent on when the gauge was made) and these transistors stop working after a while. You can replace these items if you are so inclined, there is a lot of literature on the web about what components to use, but it will still be a 35 year old tachometer that may be near the end of its life.
I'm on page 2 of this thread and can no longer see your picture so I have to do this by description, not numbers. The spade lug on the piece of brown circuit board is "hot". It receives switched 12V. Most of the green wires on Lucas wiring schemes are switched, fused 12V.
The two bullet connectors are the ends of a loop of wire inside the tachometer. I'm going to try and NOT confuse you but this can be complicated so read through the following two paragraphs a couple of times.
On factory installations of this tach, one of the bullet connectors is attached via a white wire to a switched terminal on the ignition switch, the other bullet connector is connected via a white wire to coil (+). Thus... anytime you turn on the ignition (and the points are closed), power to the coil flows through the loop of wire inside the tachometer. When the points open and close, the tach's internal induction loop makes a magnetic pulse that the gauge uses for its input signal.
On aftermarket installations of this type of tach, the general rule is that you pull two (2) white wires from the passenger compartment. One goes to the coil, the other to the distributor. You disconnect BOTH ends of the white/black wire going between the coil (-) terminal and the distributor. (Please note that is coil (-), NOT coil (+)). The ONLY reason this is done on aftermarket installations is that the gauge manufacturer is trying to spare you having to pull apart your ignition switch wiring. Functionally, the two wiring schemes are the same. When the points are closed, power flows through the induction loop inside the tach. Regardless, one bullet is connected to coil (-), the other to the distributor terminal where the white/black wire was before.
Were I you, I would follow the second wiring method I proposed. Pull two wires to the distributor and coil. If you notice strange behavior on the tachometer, switch the connection points of the two white wires (i.e. Move the wire connected to the coil to the distributor and vise versa). This only reverses the direction the current is flowing in the induction loop. If switching the white wires helps... great. If it doesn't, and the engine runs OK, all you can do is check your earth and power connections. If no wiring problems are found, the problem lies in the gauge.
Before closing let me offer an observation. The RVI tachs have been out of production since the mid-1970s. The gauge you have is likely 35+ years old. It simply may not work any more or it may be too "tired" to read accurately. There is a mylar or polyester capacitor inside the RVI tachs that fails over time. There are also one or two germanium transistors inside the tach (quantity dependent on when the gauge was made) and these transistors stop working after a while. You can replace these items if you are so inclined, there is a lot of literature on the web about what components to use, but it will still be a 35 year old tachometer that may be near the end of its life.
#18
Doodling
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Formally known as phil.lingard
Posted 12 August 2009 - 03:50 PM
Thank you dklawson that has helped. I've wired it all up and the car started but as you predicted the needle failed to move let alone flutter. So it's of to find a new one the same size as I've already cut the hole in the MDF dash.
Cheers
Cheers
#19
dklawson
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Moved Into The Garage
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Posted 12 August 2009 - 09:18 PM
I'm not sure which year they changed the gauge type, but look for MGB tachs perhaps around 1973 or 1974. If you go any later, the type will be right but the look will be wrong. If you go much earlier you'll find they used RVI. If you go too far back (up to 1965?) they were cable driven. MG Midget (& A-H Sprites) are other good donors.
In closing. DO NOT throw your dead RVI tachometer away. Sell or trade it as you can for other parts you need. RVI tachs can be repaired and there is a market for them. If nothing else, the chrome bezel and the mounting hardware can be used on other Smiths gauges.
Good luck and let us know what you find.
In closing. DO NOT throw your dead RVI tachometer away. Sell or trade it as you can for other parts you need. RVI tachs can be repaired and there is a market for them. If nothing else, the chrome bezel and the mounting hardware can be used on other Smiths gauges.
Good luck and let us know what you find.
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