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Ammeter wiring 1974 365 GT4 2+2

Discussion in '365 GT4 2+2/400/412' started by Doug D, May 20, 2020 at 11:09 PM.

  1. Doug D

    Doug D Rookie

    May 6, 2020
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    Douglas Dwyer
    Concurrent with my engine bay rehab is sorting out some inoperative circuits, replacing seized cables, and so forth.
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    I discovered some melted wiring, heavy gauge, which looks like it went to the ammeter...which itself has been disconnected. The wires are snipped-off a few inches shy of the instrument itself.

    However, judging from my (very-hard-to-read wiring schematic) it looks like, perhaps, this was the type of ammeter that only takes a "sampling" of the current flow using smaller gauge wires? Or not?

    (I presume the ammeter failed, as happens on older cars. Are these ammeters typically repairable?)

    I love a decent schematic that didn't require a magnifying glass!

    I've come across quote a few overheated and partially melted connectors. Presumably the contacts themselves loosened or were dirtied, causing high resistance and excessive heat. Pretty typical, in my experience. All to be corrected, one by one.

    This car has an 80s vintage radio and equalizer. The wiring is hideous, almost criminally so. Gah!. I'm sure we've all seen that before.

    Anyhow, thanks in advance for any comments or advice

    Cheers
    DD
     
  2. Tojo

    Tojo Formula Junior

    Apr 12, 2002
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    Tim
    If you want a decent schematic that doesn’t require a magnifying glass go here http://www.ferrari308gtbi.com/ and buy the diagrams Paul has made. One of the best investments I’ve made for working on my car. For dirty connections I can highly recommend cleaning them and ‘treating’ them with De-oxit Gold


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  3. Doug D

    Doug D Rookie

    May 6, 2020
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    Douglas Dwyer
    Fantastic, thanks !

    DD
     
  4. raemin

    raemin Formula Junior

    Jan 16, 2007
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    R. Emin
    I am also wondering why the ammeter relies on such heavy gauge wire as the shunt (through which all the current passes) is not built in the ammeter but bolted against the relay panel. So these two big cables should be connected to both ends of the afore mentioned shunt.
     
  5. samsaprunoff

    samsaprunoff F1 Rookie
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  6. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
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    Ken Battle
    DD
    Once you have downloaded the wiring diagram take the file to Kinkos or similar print shop and get a few copies printed in large format. I have 2-3 copies 24"x32" (D size I believe). Keep one clean and mark all your changes on another.

    I believe the shunt is more like a fusible link protecting the cars wiring from a 'runaway' alternator.

    Do the large wires go to or near the ammeter? Ammeters are usually actually a voltmeter that measure the voltage drop of the amps flowing thru a fixed resistor. V=IR So with R xed, amps are proportional to Voltage drop. The resistor is usually external to the gage but could be internal. Size of wire connectors on ammeter will tell you which it is.

    My Series 2 400i only has an idot light but it still has the shunt under the wiper motor.
    Ken
     
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  7. samsaprunoff

    samsaprunoff F1 Rookie
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    Good day Raemin,

    It is possible that the car's electrical designers wanted the Ammeter's "sense" leads to have as low of resistance as possible (e.g. the larger the diameter of the wire the lower its resistance) in order to have a more accurate reading. Remember the voltage across the shunt is typically very, very small and so the resistance of the sense leads could affect the measurement.

    Cheers,

    Sam
     
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  8. Doug D

    Doug D Rookie

    May 6, 2020
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    Douglas Dwyer
    Thanks, everyone, for the replies.

    I'll take a close look but I think my relay board hasn't been monkeyed with.

    As for my melted wires I could well be wrong that they ever went to the ammeter. I'll take a pic; maybe someone here can identify them

    Cheers, and thanks for the help.

    DD
     
  9. raemin

    raemin Formula Junior

    Jan 16, 2007
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    Lyon (FR)
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    R. Emin
    There are some references engraved on the shunt : A50mV100, which could read 50Amps for 100mV. With such a low voltage (<0,1v), the big wires could indeed make sense.

    Unfortunately these wires aren't fused and the connectors are not shielded in anyway. On the ammeter side these are bolted and the bare nuts are just exposing permanent positive from the battery. So one would be better of not to short these 4mm cables while playing with the instrument cluster. As I am messing a lot in this area I have applied some (ugly) tape on the ammeter terminal. If anyone comes up with a clean and safe way to isolate these live wires, please let us know...

    As far as Doug melted cables are concerned. A pic would help... Careless audio installation makes me think about the followings:
    1) Grey permanent positive cable for the radio .
    2) Windows heater cable (that's the "accessory wire" for the audio)

    High amperage cables next to the ammeter could also well be:
    3) Fuel pumps cables, same area and quite high amperage also (should not normally occur as these are fused)
    4) Fog lights cable (I would expect the switch to act as a fuse first)
     
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  10. Doug D

    Doug D Rookie

    May 6, 2020
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    Douglas Dwyer
    Thanks Sam.

    I've ordered and rec'd the wiring diagram as suggested above but haven't had a chance to study it yet; it'll be a huge help

    I've attached some pics.

    One shows the yellow melted wire at the RH fuse box, extreme RH cavity.

    Another shows the same melted yellow wire in the neighborhood of the ammeter, burned female spade connector still in place. It is bundled with some wires that appear to be snipped-off and terminated with shrink tubing. These other wires in the bundle are red, red/black, yellow/black, and black.

    The third pic of the instruments shows the ammeter (which uses ring terminals....so the yellow wire obviously does't go there) and the oil temp gauge, which has obviously suffered heat damage. The ammeter looks OK, visually. The wiring at the oil gauge has been modified with Scotch-lok connectors. My guess is that the PO is taking 12v "key on" voltage from one of the other instruments to supply the oil temp gauge.

    With the good diagram I'm pretty sure I can't sort all this out but, still, any comments would be welcomed

    Cheers
    DD
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  11. raemin

    raemin Formula Junior

    Jan 16, 2007
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    R. Emin
    Green from the instrument cluster is a "key-on" positive. Unfortunately that's not where one should tap the wiring for audio as the current is passing through the fragile/expensive steering column switch. This yellow cable coming from the stalk already has to feed coil, dynoplex, windscreen wipper and a few other things. Adding another power hungry accessory is not a good idea.

    As I've mentioned earlier for "accessory" current one should tap the rear window heater cable (no need to split the cable as there is even a connector left on the window heater toggle switch. This harness is much more suited to audio: it's operated through a 30amp relay, and the cable itself is reasonably beefy (2,5mm²).

    The other cables (red/black, red, black, black, yellow/black) are probably from the fuel/oil/clock instrument harness. If correct, the melted cable with 6.3mm connector is for the clock. Presumably your audio junky attempted to tap a permanent positive here instead of using the factory provided grey cable...

    I can see now why all this mess could happen: the purple wire on the fusebox was somehow reverted. This cable is the one providing current to the fusebox, it should be connected to the background pins, whereas it has been placed in the foreground pins, which bypasses the fuse...

    At least all the mess seems to be isolated between the fusebox, instrument cluster and column stalk, so that's all located on top of the dashboard which makes it an easier fix. Time to read Paul Bennet's diagram, invest in a good crimping tool, Fastin Faston connectors and a few meters of automotive cables...
     
  12. raemin

    raemin Formula Junior

    Jan 16, 2007
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    R. Emin
    I just have to correct my previous assumptions...

    Purple cable could well be from the AC drier but nothing sure as the cabling of your fusebox is confusing. I know the 365 is somehow different than the 400 (which I have), but a rapid review of the 365 owner manual shows that the green cables (radiator fans) should be connected to fuse [M] & [N] (just like the 400), not to fuse 'U' as is the case here.

    I suspect that you will find quite a few other mixed up cables, so take your time to properly undo whatever the previous owner did...
     
  13. Doug D

    Doug D Rookie

    May 6, 2020
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    Douglas Dwyer
    raemin, thanks for the insights on the wiring.

    Also thanks for the tip on Fastin Faston. I have a ton of various connectors and wiring repair supplies but I'm always looking for suppliers for connector bodies and so forth.

    Cheers
    Doug
     
  14. samsaprunoff

    samsaprunoff F1 Rookie
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    Good day Raemin,

    Good sleuthing on the markings and most likely you are correct. I have a high resolution millohm meter and so I will measure the shunt to see how it compares to the printed markings. If the markings prove accurate, then at 50A the shunt would dissipate 5 Watts of power which is a fair amount of heat given that convection cooling and within a confined space.

    As for the Ammeter's lack of shielding... you are quite right... this can be quite problematic and makes it mandatory to disconnect the battery if one is doing any electrical work and/or working underneath the console, dash, etc.

    As for a solution for masking these connections... I have a few ideas that I will try and if I find something that is reasonable I will certainly post up.

    Cheers,

    Sam
     
  15. samsaprunoff

    samsaprunoff F1 Rookie
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    Just a heads up, but automotive rated wire is really low quality wire...there is a reason why it is inexpensive as compared to "proper" wire. I always try and use Industrial rate wire (minimum 300V rating with approval markings) if I can (e.g. color match, overall size, etc), as the conductors are made to a much higher level (lower resistance), but also the sheath is comprised of materials that do not self-ignite if the wire is overheated (too much current). Adding to this if you electrically stress Auto rated wire too much it releases some very nasty carcinogenic compounds (almost like a acrid odor) which is not good. So... if you must replace some wiring try and use an industrial and approval (UL, CSA, CUL, etc) rated wires, as you and your car will be better for it and the additional cost will be minimal.
    Cheers,
    Sam
     
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  16. raemin

    raemin Formula Junior

    Jan 16, 2007
    378
    Lyon (FR)
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    R. Emin
    Judging by the discolouration of my relay panel, the ammeter does not get insanely hot. When combined together The coils of the bosh relays are consuming a lot of energy (250ma each): with the key on, after a few minutes, the whole board gets quite hot, but as long as I can touch them I consider this as acceptable. The worst consumer is the wiper timer! I would have never imagined such a dummy device would get hot to the point it can melt the panel. I am reluctant to upgrade it to a solid state device, but that's definitively an accessory that must be mounted with a few washers in order keep it clear from the board and to allow for enough airflow and cooling.

    I do indeed try to avoid as much as possible "modern" automotive wires: these are much cheaper but do have a thinner protective insulation. Sadly, the old styles automotive cables with thick insulation are harder to come by. I am now buying my cables from building and industry suppliers.

    As far as the 400 is concerned, mine is a late 400i gen 1 (December 1981) and I was positively surprised by the wire gauge: most of the 1.5mm² cables of the diagram are upgraded to 2.5mm², and quite a few cables are upgraded to 4mm² cables. If it were not for the fusebox this is a beefy setup. All in all they finally got it right in 81-82. Too bad they decided to "upgrade" the 400 gen2 with the flimsy relay & fuse box that plagued all Ferraris of that era.

    The bean counters had already done a bit of homework though: the Fastin Faston one-way housing (white) are of a lesser quality than what was used for the 365 (these are black and do not melt as easily). So @Doug D do not downgrade your connectors: if you need to replace the terminals just save the original housing (i.e new terminal in old housing). For the lack of stock 365 housings, I am replacing my housings with hard silicon housing (https://www.classicautoelec.com/fr/isolants/624-manchon-isolant-silicone-dur-pour-cosse-plate-femelle-63mm.html).

    For the record, that's what my fuel pumps connectors looked like (these are attached to the fusebox)...

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    I am sourcing my connectors terminal from 3wayComp on ebay. They have both regular and quality terminals. The "Quality" terminals are indeed made out of a thicker sheet of metal. Errebishop in Italy is also a good supplier. Their fuseboxes are made in Europe with terminals suitable for 4mm² cables (sold separately). Tested quite a few Chinese fusebox, 12 times cheaper than their Italian counterpart, but I got what I paid for...

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  17. samsaprunoff

    samsaprunoff F1 Rookie
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    Good day Raemin,

    I do not think that the issue is with the faston housings, but rather the current flow through these circuits that the faston housings are connected to. For this type of heat discoloration to occur, you would have to have a large localized amount of heat. The only place for this heat is at the connector and so either the wiring size was too small (so power/heat generated by current-squared * wire resistance) or an increase in resistance in this connector (Resistance increase via oxidation would cause the current-squared * overall resistance to increase). Replacing the housings could be masking the real issue and I would first check, inspect, and clean these terminals (both male and female) and then verify that the voltage drop is very, very low and also measure your inrush and steady state circuit current to see what this value is. Although the fuses are rated at a current level, they do not expire if your circuit is operating at this current level or a bit higher for some time... could be several hours. In my experience with analyzing Ferrari electrical circuits and fuse blocks I have found that the overall circuit current to be about 1/2 the rated fuse size, but no more than about 75%... which is in agreement with the rules of thumb used in practice. If you are seeing your average circuit current to be greater than 75% of the rate fuse current, then I would investigate the circuit to determine what is the drawing the excessive current.

    Cheers,

    Sam
     

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