12V to coil all the time (engine wont turn off)

[taz]

Hi Folks

Hoping you can help..

1971 Saloon (no tacho).

1st symptom was a completely dead battery (0.0V across the terminals).

Replaced battery, started normally, 2nd symptom - engine wont shut down via the ignition switch.

Removed and tested ignition switch. Appears to be working correctly (switching Pin1 to Pin2&4 in the ignition "on" position, then Pin1 to Pin3 to activate the starter motor).

With the ignition switch removed and battery connected, I measure 12V on one of the wires going to Pin1 and also on one of the wires (white) going to Pin2 (which I think should not be happening).

Re-connected battery (with ignition switch still removed) and measured a 0.5amp current draw at the battery. Also measured 12V at the coil (no ballast resister).

Disconnected the ignition wire at the starter motor solenoid (with ignition switch still removed) - still saw 12V at the coil.

Any guidance or suggestions would be most welcome.

Cheers
Taz

[Phil Nottingham]

Your car should have the thief proof coil set up (no ballast) and key switch on the column. It looks to have been wired incorrect. The coil should be fed via the switch from the unfused side of the fuse box.  You need to trace the cables

[taz]

Thanks Phil

Mine has the ignition switch on the binnacle.

I've scanned (and enlarged) the wiring diagram in the workshop manual and my wiring appears to follow it (at least the connections I've checked).

Eg two wires go to the coil +ve terminal. One is the shunt wire from the starter solenoid. The other comes from the ignition switch with a resistance of about 1.8ohms. So whilst I don’t have the ceramic ballast resistor, it is possible that I have a ballast resistor wire in the loom.

There is no power coming from the shunt wire to the coil when the battery is connected and ignition switch removed, so the solenoid switch is OK. Hence it must be the wire from the ignition switch (possibly with in-line ballast resistor).

Trying to trace the wires: The two wires at the coil disappear into the wiring loom. Today I removed the binnacle and the white wire that connects to Pin2 on the ignition switch (which now incorrectly always has 12v) also directly disappears into the wiring loom.

Whilst plausible, it seems unlikely that I would have a short-to-12V inside the loom. More likely to be something else...

Cheers
Taz

[enigmas]

Loosen the securing nut on the positive power feed to the coil. There should be 2 wires. One a ballasted feed and the other unballasted. Remove one wire at a time with the engine running. The wire that cuts the engine with the ignition switch in the off position (whilst the engine is still running) is the errant power feed.

[taz]

Thanks Enigma

I think you are onto something. Whilst I've disconnected the shunt wire at the solenoid and the coil still has 12v, it is plausible that the short-to-12v is in the wire loom going from the coil to the solenoid and not from the coil to the ignition switch.

The two wires to the coil are soldered onto the same spad connector but I will separate them on the weekend and test

Cheers
Taz

[Phil Nottingham]

The ballast shunt was only used on very early models with n/s inner wing coil + ballast. 1969 models had a pink resistive wire in the loom which travels on top of the parcel shelf - coil only on n/s inner wing. The 1971 models should have the Thief proof coil on the o/s servo and column ignition switch. The ignition wiring is quite different.

Yours must have been modified incorrectly or perhaps its an earlier car. What is the chassis number?

[taz]

Thanks Phil. Perhaps they changed it to suit Australian Design Rules. Chassis number is 84100520D

Cheers

[Phil Nottingham]

Perhaps the export models retained the temp resistive wire in the loom (pink) Its joint can be seen sticking out of the loom at approx. the centre of the parcel shelf at the rear of the radio/centre glove box. This set up had no starter solenoid shunt that the very early models had with the ballast at the side of the coil, Both arrangements are better than the ridiculous so called thief proof coil set up on the 1971 models onwards instead of the steering lock which all other UK car manufactures adopted then. Some Series 3 export Land Rovers where this immobilizing requirement was not needed just had a bracket in the steering column to take the normal old style dash switch

[taz]

Fortunately, splitting the two wires at the coil isolated the fault to the shunt wire from the solenoid. Somewhere between the solenoid end and, the coil end, is a short to 12v.

After disconnecting the shunt wire at the coil the ignition switch is starting and stopping the engine as it should. Starts fine too (does not appear to need to shunt wire).

I also disconnected the shunt wire at the solenoid - otherwise I had a 600mA parasitic load on the battery (with everything off).

I'm going to have a close look at the shunt wiring harness when I next have the vehicle on the hoist, but for now I'm functional again.

Thanks for the help and guidance.
Cheers,
Taz

[taz]

Found the problem...

The wiring harness running to the starter motor solenoid was pinched between the chassis and the heavy 12v cable running from the battery to the starter motor. The harness was being abraded from above by the heavy 12v cable and from below from the chassis. Insulation from both the heavy 12v cable and the wiring harness had rubbed away at the contact point. Hence the reason I had 12v to the coil at all times. Also one of the harness wires had rubbed thru to bare copper where it made contact with the chassis.


Cheers

[taz]

Previously I was also experiencing brief intermittent missing (momentary cut-outs) which is now no longer occurring after fixing the wiring loom.

[Phil Nottingham]

Thanks for the update - it is helpful to others. I am pleased you have sorted it