FERRARI 308 SPEEDO SENSOR QUESTION

My speedo sensor is dead and I bought a new one PN124146 and the wires are yellow and brown where my old sensor had a green and red/black wire setup. The plug will slide right on but before I do that I read some information on this site that the wires are reversed and need to be switched. I know my speedo is good because MoMa Manufacturing just serviced it but before I plug in I want to know if I need to switch the wires. If anyone knows I would appreciate it.

Alternatively, if anyone knows how to ascertain which wire is the hot wire on the sensor that would solve the question as well.

 

Make sure the new yellow matches the old green (and the new brown matches the old red/black) as per the linked tutorial below:

It seems odd that you would have to swap wires on a part with a Ferrari part number. Do the sensors look the same?

As per the warning in the tutorial, don't put volts on the wrong terminal as this could damage the sensor circuit.

 

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This post is what I am worried about.

 

Very concerning. That post seems to be opposite of what the tutorial is saying.

Experts?

Are the wire colours on the instrument side of the plug visible?

 

I don't have any wiring diagrams for the 308, but on the 328, there is a green/white wire providing +12 volts (fuse power) to the sensor. A red/black wire carries the speed sensor signal back to the instrument.

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If you look at the repair tutorial, it has this diagram:

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If the wire colours are not visible on the instrument side of the sensor plug, can you look for 12 volts on one of those wires (ignition on and the sensor not connected)? (black voltmeter probe to earth)

 

Thanks. I know that the green wire from the speedo to the sender is hot. The only question is whether the hot on the new sender is the yellow or the brown?

 

By the repair tutorial, it should be yellow. The repair tutorial is so detailed, I think I would put my faith in that (unless the maker of the sensors is known for making manufacturing errors and mixing up their wire colours). As guru Steve Magnusson was involved in the conversation (on the other website) I would contact him here on FChat to see if he has any further information @Steve Magnusson

If there wasn't a risk of damaging the sensor by reversing the polarity, I would follow the test procedure (although that involves sourcing a 560 ohm resistor).

 

Sorry, I misread that. Are you saying the green wire goes to the speedo? I really think I need some 308 wiring diagrams.

 

The power wire on a 308 from speedometer head to the sender is green. The signal wire is red/black. The speedometer has a separate ground that is solid black.

 

OK, I'm lost. I definitely need some wiring diagrams. What year/model is your 308?

 

It is a 1976 Vetroresina SN19333 which is an early car. It was #30 of the RHD cars.