Introduction

I’ve installed a new wiring harness in my 1965 Series IIA. The previous harness was original, and was destroyed in a fire caused by a short in the the ignition switch. I’ve put this page together so that others can learn what I’ve learned and maybe have an easier time of doing this job.

Specifics of my IIA

I’m pretty sure that my IIA is considered ‘early’. Check out Lloyd’s page of IIA information for details ion the differences in the various years that the IIA was produced. Here’s a list of the variable features that I have:

• separate windscreen-mounted wiper motors
• light switch is on the ignition
• wire-spoked steering wheel (although that doesn’t apply to the wiring)
• headlamps in the breakfast
• originally positive ground

Materials

To install the harness, you will need the following materials:

• From the Workshop Manual (part #4611):
  • Photocopy of circuit diagram for the IIA 2.25l Petrol Model, Series IIA (page P-8 in mine)
  • Photocopy of flasher circuit diagram, switch on steering column (page T-60, Fig. T-70 in mine)
• Test Lamp Do not try this without one! (I learned this the hard way)
• The wire color document from the RoverWeb
• Wring Harness (See Rover Web for suppliers thereof). Mine came from British Pacific and matched the circuit diagrams closely.

There are some circumstances under which you may want to determine whether a wire is conducting electricity properly. To do this, you will need an Ohmmeter or a digital multimeter (DMM). Whenever one side of a wire is hot, and the other is not, use a DMM to measure it’s resistance. If the DMM reads infinity or a very large number, then the wire has an open (broken circuit) in it, and it should be renewed. If the wire is part of the harness and the harness is new, send it back.

Getting Started

When you start out, try to lay the new harness along side the old one. Then go through and make sure the new harness has all the connections you’ll need (it’s OK if there are extras). Then go through the circuit diagrams and determine what all the connector do by tracing through the wiring diagram.

Tips on Reading Circuit Diagrams

If you’ve never been exposed to electrical circuit diagrams before, they can be somewhat daunting. But don’t fear, as they’re really quite simple. Your Land Rover either has a 12Volt battery or two 6Volt batteries, or two 12Volt batteries. They are connected to three parallel circuits in the Rover via a thick cable to the starter switch or starter solenoid:

• the horn circuit
• the starter circuit
• everything else

By circuit I mean a connection from the ‘hot’ terminal of the battery through some electrical equipment to some conducting circuit to the ground terminal on the battery. I purposfully do not say ‘positive’ or ‘negative’, as some (Suffix C and beyond?) Land Rovers are negative ground (the ground terminal is the negative terminal) and some (Suffix B and before) are positive ground. The usual conducting material back to the ground terminal is the body or chassis. “What?!” you say, “I’m touching the circuit of my Land Rover just by being in the car?”. The answer is both yes and no. Think of electrical components (starter motor, lights, ammeter, horn, etc.) as distance through which electricity has to flow, and conducting materials (wires and yes, the frame or body) as being a connection which involves travelling no distance. This isn’t strictly correct, but is right for purposes of this discussion. If you are touching a conducting material at ground (i.e. the frame, body, or ground terminal), then you can think of the electricity as already being back at the ground terminal, and you’re not really touching a part of the circuit through which electricity has to flow.
Grounds are marked as four progressively smaller lines perpendicular to the circuit they are in on the circuit diagram. Think of them as a connection back to the ground terminal on the battery. In some cases (such as the starter motor), they are on the circuit diagram, but not marked as such.

Here are some things to remember when looking at your harness and your wiring diagram.

• Whenever the diagram shows two or three wires, there are actually two or three wires. It’s not just electrically the same–the wires are actually supposed to be there.
• The presence of three wires in the diagram does not necessarily indicate that there are three separate connectors. On at least two connections in my harness, there were two wires hooked up to the same connector tab. The number of wires, however, was always right (see above).
• The markings on the diagram may not match the markings on your parts exactly. For example, my circuit diagram had markings A1..A4 on the fuse box, but the labels on the fuse box were 1..4.
• Sometimes when the markings are there, and they are the same, it’s difficult to read them. For example, I couldn’t find the marking on the ‘S’ terminal on my ignition because it was covered with grime. Keep looking if you can’t find something.
• Use a flashlight (even in the day time) to find markings on components. I found several that way, and at least one of them was hooked up improperly when I discovered that.
• Lines on the circuit diagram connecting labeled connectors in the fuse box represent fuses.
• Sometimes the wire colors on your Rover may not look right. On mine, the red wire going back to the tail lamps was originally insulated with red cloth. Over the years, this became black from road soot. I had to try several different combinations before getting my tail lamps to work  Further, the Green/White turn indicator wire going to the rear looked like a Green/Yellow wire after 31 years.
• Don’t guess, or if you do, make a note of it. When you make every connection, make sure you can trace it back to the ciruit diagram, and you know what you’re connecting. If you make a note of where you guessed, you can go back later when things don’t work..

Installing the Harness

When installing the harness, try to follow the original one as much as possible. It’s a good idea to make a note of the color of each wire and where it was attached on the old harness. What? You say that you wouldn’t be replacing the harness if it had(n’t): burned up, existed at all, been eaten by squirrels, etc. Well, then, just make a note of what (if any) connections exist. It’s not imperative, but can help save a lot of trouble later–especially if you have some nonstandard equipment.
Once you’ve installed the harness, start the car. If it starts and everything works, then great! Go have a Guinness. Otherwise, read on.

So, It’s Not Working, Eh?

If you’ve gotten to this point, stop. Go have a Guinness. You’re going to need it. All trade schools teach that the proper preparation for debugging Lucas electics is to drink a pint of Guinness.
Starting with the battery, trace the circuit both physically and electrically. It has been suggested that making your own diagram can be of use at this point. Also, this is where the photocopy of the circuit diagram comes in handy (as opposed to the original). Mark off circuits found to be good after performing the test. That way, if you get interrupted, you’ll know where you left off.

Debugging the engine electrics

This is where we attempt to determine why the car won’t start. If your car starts, but you’re having problems with lights, accessories, etc., skip this section.
Attach the test lamp to the ground terminal of the battery (if you’ve done a ground conversion, or your vehicle was originally negative earth, then that’s the one with a minus sign, if not, it’s the one with a plus sign, if you don’t know then look for one with a cable that goes to the enine or chassis, or possibly both–that’s is the ground terminal).

Checking circuit from battery to starter switch

Now follow the fat cable from the hot (non-ground) terminal on the battery to the starter solenoid, or starter switch (if you have a solenoid, this document doesn’t address it’s components–other than the connection from the battery to the solenoid, and from the solenoid to the starter motor. I’ve only done this on my Land Rover, and mine has a switch). There should be two brown leads attached to the battery side of the starter switch, and one white lead going from the ‘other’ side of the switch to the coil. The switch itself is on the bulkhead (firewall to us yanks) and is between the fuse box and the mixture switch, and just a little below the mixture switch. Test the connection of the battery to the starter switch by touching either of the brown leads with the probe from the test lamp. If the lamp lights up, then this connection is good. If it doesn’t these wires are probably causing the problem. See above to determine if a wire is bad.

Checking circuit from starter switch to starter motor

Place the probe of the test lamp on the cable running from the starter switch to the starter motor, then have someone push the starter button. If the lamp lights up and you hear the starter motor, then the switch is good. If the lamp lights up and the you can’t hear the starter motor, then either the motor is broken or not grounded.

Checking circuit from starter switch to ammeter

Now check the circuit from the starter switch to the ammeter by grounding out the test lamp on the ground post on the back of the instrument panel, and probing both sides of the ammeter. The test lamp should light up on each side of the ammeter. If it doesn’t, then your ammeter is toast, and that is the problem (all electricity to a IIA that doesn’t go to the horn, the starter motor, or the inspection light socket goes through the ammeter–which is why it’s a good indicator of electrical failure. As a field repair the ammeter may be shorted. This involves connecting a wire to each terminal on the ammeter.

Checking circuit from ammeter to voltage regulator

The voltage regulator is a black box mounted on the bulkhead of the engine compartment with tabs sticking out of the bottom of it that have wires connected to them. If anything in that sentance seems wrong to you after looking under your bonnet, then there is a problem. With the ignition off, the tabs marked AI and A should be hot, and the rest should not. With the ignition on, the tabs marked F and D as well as the first two, should be hot. If D is not hot when the igition is on, then look at the charging light and the white connector from IGN on the ignition switch and the yellow wire in the instrument pannel and the engine compartment. If F is not hot when the ignition is on then you may have a blown generator or alternator, although that is unlikely, so check the connections on it. It is attached to what is commonly referred to as the engine harness, which attaches to the main harness and then goes around the block, behind the fan, and to the alternator/generator/dynamo.

Checking the coil connection

With the ignition on, both sides of both fuses in the fuse box should be hot. If they are not, you may have a bad iginition switch (that was my problem), if they are, then check the coil. When the ignition is on, the white wire on the coil should be hot. When the starter is engaged or the engine is running, the small wire (not the big cable) from the coil to the distributor cap should cause the test lamp to flicker when the probe is touching. If this doesn’t happen, you need a new coil.

Debugging the Instruments/Accessories/Lights

This isn’t so hard.  Here are some things to remember:

• The charging lamp works by having current going to both sides, then when the generator/alternator stops generating current it becomes ground, and the lamp will be illuminated.
• The oil pressure warning light works by having current going into it at all times. When the sensor senses less than sufficient pressure, the wire leading to it grounds out, leadint to the lamp being illuminated.
• The cold start lamp works just the opposite.  When the engine is cold, the thermostat isn’t grounded, but when it heats up, the thermostat grounds out.  This causes current to run from the battery to the light, then through the switch on the bulkhead which is actuated by the choke cable, then to the gound on the thermostat.  This lights the indicator.
• Turning indicators: If your flasher is mounted like was (vertically), then you’ll want to mount it horizontally, so you can see the labels on the spade connectors.  Once the harness to the turn signal switch is properly connected inside the dash panel, then you need to make the proper connections in the engine compartment.  Be sure you do not confuse the Green/Yellow Oil Pressure Indicator Wire with the Green/White Turn Indicator Wire. This happened to me, and wasn’t fatal, as my rear harness was so old, the white on the turning indicator wire was white–it looked yellow to me.  It just took me a while to figure out why my turning indicators didn’t work  The statement above about not hooking up wires unless you know what they do applies here.
• A frequent failure point for headlamps is grounding.  I ran extra grounds to the body of the rover in the breakfast.

Copyright © 1996 Christopher H. Dow