What's This?

[Joel]

Hi,

 

Been having trouble trying to get a tacho signal to my new gauges. After poking around at the coil end, I found this (see below):

 

Sorry for the out of focus image. The black end says: 07230 W-GERMANY 0 119 910 002 FORD 86GB17K499AA KT

 

And the other end says: Ford SL 102.10

 

I identified the wire I was after as being one of the ones attached to it, but the gizmo doesn't seem to be passing a current through. So I disconnected it, joined the the two detached wires together and hey presto my tacho works just fine.

 

So what is it and what kind of long term damage am I doing by not having it in place?

[Guest TerryBarry]

Joel,

It's a capacitor - it's normally wired in the feed line from the coil to the tacho connection on the Ford Instrument cluster.

If you've got the Haynes manual its item 145 on diagram 1a Ignition variations (carb) and diagram 4 (EFi) and it's described as a suppressor.

 

The same diagrams seem to show the possibility of it being replaced by a bit of wire.

 

My knowledge of electronics doesn't extend to explaining why it's there. But I usually work on the theory that Mr Ford doesn't spend extra pennies on anything that could be eliminated.

 

HTH

 

Terry

[Longboarder]

Agree with Joel that it should be a capacitor but I thought they normaly ran coil neg to earth and were part of radio supression. No damage will come of removing it. If it is a capacitor I cant see what its doing between coil and rev counter.

 

Nigel

[Guest daveg]

All

 

That doesn't look like a capacitor to me!

 

If it was then it should run to earth if providing suppresion, or in series if protecting the tacho from DC current...if the former then radio might be a little noisy on a.m if latter, oh dear too late

 

Mr Ford might waste pennies if production line cost would increase due to extra models...capacitor are pennies

 

If it works then I would leave well alone

 

Dave

[Joel]

Thanks chaps,

 

The mighty combined brain power of friends and family( ) had come up with a majority decision that it was some kind of radio interferance suppression device.

 

As things stand my tacho works fine and I don't have a radio fitted, so I'll leave things as they are.

[Guest Bernie]

Put in it's simplest terms a capacitor will pass some current on ac but not dc. Used in a suppression mode it will provide a low impedance path to earth (negative) for the unwanted high frequency switching transients at the coil, but present a high impedance path to the DC element of the waveform there.

 

Used in the line to the tacho the principal is the same. Any swithing (ac) on the line will be passed to the tacho to trigger the internal tacho circuitry, but it will provide dc isolation between coil and tacho.

 

Capacitors (suppressors) have to be selected for their application. The value of the capacitor, the characteristics of the switching circuits, the voltages present, and the input characteristics of the tacho will all have some effect on how much of the switching current is passed through. It could therefore be that where a capacitor in line with one tacho worked, it does not with a tacho from a different supplier.

 

If it works with the capacitor in line then keep it, as it gives a degree of dc isolation from the ignition primary circuits. If it doesn't work with the suppressor in line then leave it out. I believe that most modern tachos have this type of dc isolation already built into their circuitry so no damage should result.