I took factory dist off to change points and cap. (1966 FHC). I’m confused, the new cap’s body is grounded, so where does it’s remaining wire get connected ? The side of the 22D has it’s hot lead+ (or what I thought was the (LT) low tension 12v+ feed, The contact break (CB) gets that 12v and is insulated by the nylon nut piece, but where does the cap’s wire go ?
As an aside, I’m considering the 123Dist, but does the 123Dist allow it’s internal advance curves to take over command of higher RPM “advance” with the manifold vac feed closed off ? Or does the 123Dist still require a vac feed of the EType manifold ? Apparently there is a vac-version 123Dist and a non-vac version of 123Dist. Also, there is a Youtube UK Chap noting that the 123Dist static timing requires not connecting ground, but why ?
Does not sound like a stock cap to me. On one of my other cars the distributor cap has a metal surround that gets grounded but I don’t see how a usual plastic phenolic cap would use a ground. Got a photo?
My suggestion to anyone doing a rewire of their car would be to snip the existing wires and not simply disconnect them. Then make up your own wiring chart and compare it to the new harness. By snipping them you have the correct color wire going to the correct part. It may not be 100% correct but it’s better than nothing and certainly better than rushing to start the job only to spend hours scratching your head.
I meant the “cap” capacitor wire to the nylon post (one side of the points).
By body ground, I meant the dist casting is ground and the side terminal (LT) is 12v.
The nylon insulator area is what confuses me, are both the 12v (LT) lead AND the capacitor leab BOTH
connected in same area of nylon lug (rather than top area which is ground via the nut.
Then when point gap is closed, that LT 12v is directly shorted to ground (under no load).
That’s confusing to me, I see why the nearby capacitor get 12v during the closed gap, but why short LT (low tension) 12v to ground ? I did a voltage drop test and found that the dist 12v short actually drops the voltage to the starter motor. With the dist LT connector OFF, I get more voltage to starter. Sine the ignition coil’s high voltage fires the spark plugs, then the 12v LT feed is only useful for setting initial static timing, after static timing is set, that LT 12v feed can be disconnected, (since the rotor coil’s voltage fires each plug) ?
The points don’t short +12V to earth. The plus side of the coil is fed +12 via the ignition switch, and the points open and close the -12v side of the coil.
Here’s an overview:
One clue is the color of the low tension wire: White with a black Tracer. In the Lucas way of doing these things, white means the unfused circuit from the ignition switch. The black tracer says this is providing a path to ground under some circumstances.
My understanding is that the white wire (with this ground) powers the coil, building the charge. Interrupting that power (points open) causes the field to collapse and the charge to be released via the high tension lead.
Disclaimer - I am not an EE and no expert here, but I did watch ‘Mr Wizard’ every Saturday morning.
I get that the points are opening and closing a ground path, but why does the moveable portion (via dist cam lobe) of the points section include the 12v (LT) wire side of dist body ? Why the inclusion of that LT 12v on the nylon insulator side of the points ? I get that dash key turns on 12v to coil (white wire) and the coil negative wire (blk/wht) and center coil energizes each spark plug 153624 CCW. But other than setting static timing, why is there 12v inside the dist on the points ? (Since in theory car without run without the internal dist capacitor).
My concern is the situation where the dist points (closed) are shorting (LT lug wire side of dist) 12v to ground and under no component load, as the 12v takes the least resistance to earth; thus bypassing that nearby capacitor that’s wired in parallel with direct path to ground (when points are closed).
Do you mean you’ve got a 12v+ wire connected to your distributor?
Or do you mean you’ve measured 12V inside the distributor at the post where the cap and points connect?
With a mechanical points distributor you don’t have +12 connected directly to the distributor. If you put an electronic pickup in to replace the points then these need +12 feeding that “points replacer” (any I’ve seen at least).
Are you checking with a lamp? It will light as you open the points, but that is the (reduced) voltage you are seeing at the negative side of the coil.
YES, I’m (ohm meter) seeing 12v inside the dist on one side of the points.
Some background: I bought the car in 2014, found evidence behind dash that of fire damage from one of the driver side fuse holders. The prior owner knows not why, he parked it and it sat since 1981. Replaced that burnt fuse holder but the wires are as the factory wired it. Still using the 1966 wiring harness.
If it’s wired correctly then what you are seeing is the voltage at the negative side of the coil. Unplug the white from the coil and double check (with your meter on Ohms) that the wire feeding the points goes (only) from the negative side of the coil to the points.
The coil is just a long winding of copper wire - to the Ohmmeter it “looks” like a wire. Because it is a wound in a coil it produces a magnetic field which drives the HT side of the coil.
The purpose of the capacitor is to slow the voltage rise across the points when the points open so that the spark plug arcs over before the points do, this arc over (spark) discharges the magnetic field that built up in the coil while the points were closed. So the purpose of the capacitor is to keep the points from arcing, and thus keep them from burning up.
Just tested '66FHC: With coil pos. and neg. correctly connected (white 12v and white/black negative) I get 12v at the dist side terminal, as well as 12v on both + and - of the coil !!! With coil wires disconnected I get 1v at the dist side terminal and 1.5v at the negative coil wire (as I hold wire in my hand).
Would you know which dash fuse wires I could disconnect that would rule out the dash 12v path to ground but still energize the starter.
As long as the points make and break a path to ground as the shaft rotates, and the cap is across the points, then the rest is just a matter of setting the gap and timing.
I think you’re getting distracted by perfectly normal readings.
