348 wiring diagram

This might help. Also check the attached pdf, I traced out the speedo circuitry.
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All of the above came from the speedo "deep dive" thread.

http://www.ferrarichat.com/forum/348-355-sponsored-bradan/503511-348-speedo-burned-internals.html

 

Ian, since I'm not sure what exactly you're trying to diagnose this may or may not be helpful, but if you're trying to figure out exactly why your speedometer doesn't work you can save a ton of time by buying or borrowing one of those little battery operated mini oscilloscopes. I paid <$70 for one off of Amazon and I figure it saved me that much in time since it immediately confirmed that a square wave signal was indeed getting to the speedo itself, meaning I didn't have to check wire continuity or try to determine if the new speedo sender was actually putting out a signal.

Good luck in your diagnostic process.

 

Via Connector A at the fuse box.

See Post #90 and onwards:

http://www.ferrarichat.com/forum/348-355-sponsored-bradan/503511-348-speedo-burned-internals-5.html
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The problem with mine was a shorted out seatbelt ECU that was sending stray volts (10-12v) directly to the speedometer, which ultimately fried the speedo.

Fortunately I found the problem before installing a brand new speedometer (listing for $1200).

 

No bother at all. It's almost as much fun to work on this car than it is to drive it.

 

Fortunately for Ian, that's not the problem in his case. For one thing, the speedometer is still working intermittently. But more importantly, it's doubtful his car has mouse belts unless he happens to have a US version.

Ian, your issue sounds very much like mine. Using an oscilloscope to check for a square wave signal at the speedometer will confirm that theory. I left the instrument binnacle in the car but loose, with all of the gauges connected, and jumper leads connecting the relevant signal wires to the 'scope. That way I could see what the speedometer was doing at the same time I was viewing the sender pulses. The sender pulses were consistent, so it was obvious that the problem was in the speedometer itself.

I wound up replacing pretty much every component on the top of the driver board inside the speedometer and it has been working 100% ever since. I used top quality components and upgraded their ratings where possible in hopes of improving durability. I ordered at least ten of every component that was replaced, so I have seven extra sets of components available for anyone who needs them.

Here you can see what the board looked like after the repairs were complete. The red arrows indicate the only two components I did not replace. Below that is the board attached to the speedometer, before component replacement.

Good luck in the diagnostics. If you find a consistent signal getting to the speedometer it's a pretty safe bet that replacing the components that I swapped out will fix the problem. Let us know what you find.
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That looks pretty sweet Mike. You have a PM for one of your kits

My old one is still apart, plus I only sourced three of the components.

 

It took a while to get one of the ICs-- wound up sourcing it from China because it was the exact same part number as the original. Miroljub came up with a likely replacement but neither of us could find a direct crossover between the two parts so I took the safer (but more expensive) path and just ordered the direct replacements. In the end it was well worth it since the alternative was a replacement unit and this kept the original odometer reading. Hopefully our respective ordeals will help Ian and others in the future.

 

Excellent thread guys ! This is the type of information that makes this site so valuable for us diy types. We all seem to get speedo problems sooner or later. Mine quit and a new sender solved the issue. Sender was very difficult to source at the time. Are the senders back in production again ?

 

The 355 sender is the same but with a different connector, plus cheaper and more readily available. If I have to do it again, changing the car side connector on the 348 is the way to go (adds weather-pack).

(don't mind the split/broken 348 connector, for visualization only)
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Ian, your symptoms mirror the ones I was seeing fairly closely. It&#8217;s not uncommon to have an electronic component become thermally deficient, although they usually fail as they get warmer instead of the other way around. Keeping in mind that the sensor is not only a simple winding, but also contains actual components, it&#8217;s the logical culprit&#8212;most speedo problems discussed here seem to be solved by replacing the sensor, presumably because the internal seal has failed and allowed oil to contaminate the board, components, and winding.

Replacing my sensor with a new original style part got the speedometer to work for a brief time, after which it died for good. Which is when I removed the speedometer itself to inspect it for burned components and/or bad solder joints. It looked fine, but I noticed a few electrolytic capacitors on the drive board and I know full well that those deteriorate due to age and eventually get way out of spec and/or fail. So I replaced those with off-the-shelf parts, which made absolutely no difference.

Which is when I decided it was worth $70 for an oscilloscope in order to prove that the new sensor was doing its job and that the signal was making its way to the speedometer. Once that was done it was clear that the remaining problem was inside the speedo, which was when I started doing exhaustive research to try to locate the best available replacement for every component on the top of the driver board.

Although I have yet to test the original sensor, my guess is that it was indeed bad. Even if it wasn&#8217;t, replacing it made sense because of the potential for internal contamination. I&#8217;ve kept it, and would like to collect some other old ones if anyone has one lying around, as I&#8217;d like to eventually get into repairing them. In any case, a new sensor alone did not solve the problem, so either the sensor went bad and caused problems within the speedometer, or there were two concurrent issues.

Considering the age of the components and the symptoms you&#8217;ve described I&#8217;m guessing that you have a problem within the speedo itself. So you can either change components in hopes that this is indeed the case, or you can use an oscilloscope to confirm that the rest of the circuit is doing its job&#8230; whichever is easiest. Either way, I&#8217;m betting you can solve it without resorting to replacing the speedometer, but whether or not that&#8217;s worth the effort is up to you. I knew I&#8217;d never throw the original speedometer away, even if I bought a new one and had the old mileage put on the new odometer, so I decided it made more sense to repair the original. I think I had the board in and out four separate times to replace components before I got it where I wanted it, but in the end it was worth the effort, at least to me.

Again, best of luck. Let us know what you find.

 

Good that you found it. Assuming replacing the components in the top of the board would fix the problem you're looking at about two hours for the repair, as long as you have a small soldering iron and de-soldering tool and that you have the replacement components in hand. You might budget three hours if you've never done it before but it's literally one of the easiest jobs you'll do on a 348. You're especially lucky if your electronics tech buddy would do the actual soldering for you.

In case you didn't see my post in the other thread, I do have spares of all the parts I changed in my repair. No idea what shipping would cost to get them to you, but it would still probably be less expensive that having to get them shipped to you from the various sources.

 

I have a 1990 348 ts in the shop - question ; is there supposed to be voltage present on red / white wire to pulse generator . And on this car the connector was removed and hard wired in , having issues finding info on how this sender is connected - is the yellow wire for sender hooked to the green and white or the red and white

 

Translation for the non-robots here:

 

I'm sorry, didn't mean to be rude, My apologies.
I'm find issues locating information seams section L5 is left for some reason.
Again my apologies

 

No worries... I think I woke up on the wrong side of the bed this morning...

The yellow wire is the power wire and hooked up to the green/white wire.

Here's a coloured version of the applicable, early series 348 wiring diagram with modifications:

https://www.dropbox.com/t/ZOlW42j6rcJyhc7M

This excellent tutorial might prove useful

http://www.dinoplex.org/instruments/vegliaspeedosensor/

Welcome to the forum