Help? 74 Rear CDI / Fuse panel / capacitor

[turbotoo]

Help? 74 Rear CDI / Fuse panel / capacitor.

Anyone an expert at this? Or anyone have photo of 74 911 Rear CDI / Fuse panel / capacitor? I need to understand how this capacitor hooks up. Thanks in advance for any help.

[timmy2]

Just an AM radio noise suppression device. It wires up to the original style remote voltage regulator.
I don’t have a photo, but others may.
Definitely does not attach to the CDI box.

[Walter_Middie]

[turbotoo]

Originally Posted by timmy2

Just an AM radio noise suppression device. It wires up to the original style remote voltage regulator.
I don’t have a photo, but others may.
Definitely does not attach to the CDI box.

Thanks, It was attache fate CDI for some reason. The voltage regulator is missing too and the wire were taped up. I guess it was removed.

[Trackrash]

Originally Posted by turbotoo

Thanks, It was attache fate CDI for some reason. The voltage regulator is missing too and the wire were taped up. I guess it was removed.

I could be that the alternator was replaced with one that has an internal regulator, so the original regulator was eliminated.

Looks like you have some work to do.

[turbotoo]

Originally Posted by Trackrash

I could be that the alternator was replaced with one that has an internal regulator, so the original regulator was eliminated.

Looks like you have some work to do.

HA! Ive got it all figured out tother than the "noise suppression device". You no how this is wired in?

[Walter_Middie]

RPM sensor

Here's another photo that says it might be an RPM Sensor for cars with MFI.

http://www.early911sregistry.org/forums/showthread.php?133428-RPM-Sensor

[timmy2]

Noise suppressor. RPM sensors are 3 wire units and look totally different. They went away in later years when they upgraded the tachs.

Factory manual for 1970 and up shows 2 noise suppressors on this page. Both marked as 7.

With the remote VR gone there is no need for it.

[turbotoo]

Originally Posted by timmy2

Noise suppressor. RPM sensors are 3 wire units and look totally different. They went away in later years when they upgraded the tachs.

Factory manual for 1970 and up shows 2 noise suppressors on this page. Both marked as 7.

With the remote VR gone there is no need for it.

Thanks! Is this for 73? Seems this one is much different. The Noise suppressor plugs into the CDI and another source.

[john walker's workshop]

You don't need it.

[turbotoo]

The Noise suppressor plugs into the CDI and another source on mine. Doest show in the diagram.

[timmy2]

Doesn’t show in schematic as it was added when a radio was added.
That is all it was for.
As others have indicated. Not needed.
Besides, looks like that one has melted the red wire insulation in the pic. Odds are it is dead anyways.

[Trackrash]

Those noise suppressors worked with the old points type voltage regulator. The points arcing in the regulator caused the noise. Since you don't have a regulator, you don't need the noise reducing capacitor.

[turbotoo]

Originally Posted by Trackrash

Those noise suppressors worked with the old points type voltage regulator. The points arcing in the regulator caused the noise. Since you don't have a regulator, you don't need the noise reducing capacitor.

Thanks! Thats makes sense. Appreciate it!

[dicklague]

This cap is not there for noise supplession.

The capacitor is not stock on the Bosch CDI setup, but it is a good idea.

The cap is used for reserve power to the CDI. I have a Daytona-Sensors CD-1 in my 1973 and this is their recomendation in their installation instructions:

" If the battery is mounted in the trunk, a
filter capacitor is required and minimum 12 AWG
wire should be used for the connection to the
disconnect switch or power block. You can use a
10000 UF 25V electrolytic capacitor such as our
P/N 102007 capacitor kit or Mouser
(www.mouser.com) P/N 539-CGS103U025RC3
and bracket P/N 539-VR3A. Connect the 12 AWG
black wire to chassis ground near the engine,
preferably where the battery ground cable is
attached. Do not extend the black ground wire.
Verify that the engine is properly grounded to the
chassis."


FULL INSTRUCTIONS:
http://nebula.wsimg.com/f38ed282eb5687afef42c38b04a0abff?AccessKeyId=1C324 6E298A5DEFACC7D&disposition=0&alloworigin=1

I am sure this is why you have an electrolytic cat in your installation.

[mysocal911]

Originally Posted by dicklague

This cap is not there for noise supplession.

The capacitor is not stock on the Bosch CDI setup, but it is a good idea.

The cap is used for reserve power to the CDI. I have a Daytona-Sensors CD-1 in my 1973 and this is their recomendation in their installation instructions:

" If the battery is mounted in the trunk, a
filter capacitor is required and minimum 12 AWG
wire should be used for the connection to the
disconnect switch or power block. You can use a
10000 UF 25V electrolytic capacitor such as our
P/N 102007 capacitor kit or Mouser
(www.mouser.com) P/N 539-CGS103U025RC3
and bracket P/N 539-VR3A. Connect the 12 AWG
black wire to chassis ground near the engine,
preferably where the battery ground cable is
attached. Do not extend the black ground wire.
Verify that the engine is properly grounded to the
chassis."


FULL INSTRUCTIONS:
http://nebula.wsimg.com/f38ed282eb5687afef42c38b04a0abff?AccessKeyId=1C324 6E298A5DEFACC7D&disposition=0&alloworigin=1

I am sure this is why you have an electrolytic cat in your installation.

Really? You've reversed engineered both CDI designs and concluded both designs necessitate adding a capacitor for proper
functionality and not for noise suppression as in the case of the Bosch CDI, right? You do realize that the later 911SC Bosch CDI,
i.e. basic same design but 6 pins, used no capacitor.

[dicklague]

Originally Posted by mysocal911

Really? You've reversed engineered both CDI designs and concluded both designs necessitate adding a capacitor for proper
functionality and not for noise suppression as in the case of the Bosch CDI, right? You do realize that the later 911SC Bosch CDI,
i.e. basic same design but 6 pins, used no capacitor.

YUP....you read it right. A capacitor in the power source line with the battery so far away makes great electrical sense and gives you a little reserve power when needed. I high capacity electrolytic has to help with no downside.

just because Porsche did not use in years ago means it is a bad idea.

Do you want to see my data and research???

[mysocal911]

Originally Posted by dicklague

YUP....you read it right. A capacitor in the power source line with the battery so far away makes great electrical sense and gives you a little reserve power when needed. I high capacity electrolytic has to help with no downside.

just because Porsche did not use in years ago means it is a bad idea.

Do you want to see my data and research???

Yes, where are the data, i.e. Bosch vs Daytona, each with & without capacitor?
The data needs to be in graphical form indicating coil primary voltage versus RPM.

[dicklague]

Originally Posted by mysocal911

Yes, where are the data, i.e. Bosch vs Daytona, each with & without capacitor?
The data needs to be in graphical form indicating coil primary voltage versus RPM.

OK Loren, oh I mean "Dave"........let me dig up my charts.

[turbotoo]

Whew! Nerds . Love it!