When I started cleaning up the Bitter Apricot Super which was to become Danny's P,
I noticed that the wiring loom was damaged in several spots.
Typically, most of the damage was due to either exposure to excessive heat, or crushing of the wiring loom.
In all cases, the damage could have been avoided if some extra care had been taken to secure the wiring away from heat sources, and hinges and linkages.
On all P's which still retain a "standard" engine bay wiring layout, the main loom from the fuse-box around to the headlights is very likely to suffering damage, as the insulating tape cracks with age, and the supporting brackets tend to develop rusty, sharp edges.
Many P's also suffer from chronic voltage drop as a direct result of the wiring becoming corroded or brittle; both conditions increase the internal resistance of an electrical conductor, so a useful modification for P's with near-standard wring looms is to eliminate sections of old/corroded wiring and therefore shorten the route that charging current from the alternator has to travel to recharge the battery.
This Tech Tip details the procedure I used recently to tidy up the engine bay wiring on both Kerry's "new" Blue P, and her son Danny's Bitter Apricot Super.
The engine bay Wiring of both P's had been seriously "got at" by Bodgie Bros. wiring experts, and both harnesses had section's which were heat damaged and crushed.
With each P, before I "attacked" the wiring harness, I fabricated a bracket to mount the coil and ballast resistor near the lower, outer end of the alternator top bracket.
This meant that I could discard the lengthy coil lead, and use instead one of the commercially- available short leads.
These are usually about 12" or 30 cms in length, and I've been told that a shorter coil lead means less resistance to the spark, so you should have a slight gain in performance.
Also, the engine looks a bit neater when the coil is mounted closer to the distributor.
Now, this is the procedure I followed to tidy up the engine bay wiring.
1: Disconnect the positive battery lead!
2: Remove the screws, which hold the wiring in the retaining clamps between the fuse-box and the left headlights/ parking lights.
3: Carefully remove the old insulating tape from around the harness, from the fuse box connections right through to near the battery tray.
4: Dismantle the connections from the battery terminals. Mark all the wires with tags if you think that you may have trouble remembering where they will go when everything gets put back together!
5: Wipe all the wires with a rag soaked with degreaser to remove all old adhesive and dirt. New insulating tape will have trouble sticking to dirty wires!
6: Carefully examine all wires to cheek for burns, chafing or cracking. Likewise, -examine all spade connectors for corrosion, etc. Dirty or corroded connectors must he replaced.
7: The first major modification is to shorten the wires which go to the various functions in the actual engine. Identify the following wires:
Main alternator (charging) wire-large diameter, brown cable.
Alternator field wire -small cable, brown with yellow trace.
Oil pressure switch wire -small cable, white with brown trace.
Temperature sensor wire -small cable, dark green, with. blue trace. Ignition wire (+ to coil) -small cable, white.
Ballast resistor (+ to coil) -small cable, white.
Tachometer (pulse) wire -small cable, white with black trace.
AirCon compressor wire -small cable, black with red trace.
8: Separate and cut off these wires from the main harness near the battery tray, and with two exceptions, you should have sufficient lengths of cable to route them directly from the inner left guard across to the engine.
The two exceptions are the oil pressure switch wire, and the aircon compressor switch wire. These two will need to be extended using short lengths of spare wire and spade connectors, in order to reach their respective functions/sensors.
The other wires should be long enough to comfortably reach their respective functions/sensors.
9: Temporarily lay out each wire to its function or sensor.
Test the positioning of all wires before cutting off any excess length.
It is preferable that this "new" shortened harness is positioned across the top of the timing cover, tucked in behind the base of the distributor, and kept away from hot areas such as exhaust manifolds and radiator hoses.
Once you have established a safe route for the "new" harness, lightly tape the individual wires together and place the harness in its (proposed) final place.
Again, check that the harness does not rest across any sharp edges, or lie next to any sources of great heat.
10: When you are satisfied that the harness is positioned safely, carefully remove it from the engine and use good quality electrical tape to re-wrap the entire length of exposed wiring.
Wind the tape onto the harness at an angle of about 45" so that the tape overlaps itself for half of its own width, all the way along the harness.
This effectively means that a double layer of tape protects the harness.
It is also a good practise to use some sort of plastic cladding around harnesses where they pass across surfaces, which are prone vibration or heat.
11: Where-ever possible, use new connectors. Old connectors have a nasty habit of working loose at the worst possible lime.
12: To tidy up the engine bay a bit more, identify the surplus wires on the inner right-side guard, and cut them off the original harness down near where the horn wires (purple, with yellow trace) leave the original harness, and tape over the stubbed ends of the original harness to prevent the entry of moisture.
13: It is very common to find that the large brown cable, which on most P's is the original main power supply cable to the fuse-box, has severe corrosion around the spade connector where it joins the fuse-box.
In extreme cases, the power supply to the ignition and light switches can be interrupted when this connection becomes dirty or corroded.
One quick fix for this problem is to unscrew the fuse-box, and fit some kind of spacer to keep the base of the fuse-box well above the surface of the inner guard.
This has the effect of helping to keep the connections to the fuse-box drier.
14: It is also a good idea, while you have the fuse-box unscrewed, to remove each of the wires from the terminals, one at a time, and give each terminal a thorough cleanup with a soft wire brush.
A light spray with W.D. will help delay the re-appearance of corrosion on the terminals.
15: I mentioned in a previous Tech Tip article that fitting headlight relays to your P's wiring system should give you brighter headlights, as well as making your wiring system safer.
It is perhaps timely to repeat some of the warnings associated with that work-:
The main power supply wire which brings permanent (unswitched) power from the battery to your P's electrical system is capable of carrying more than enough current, in the event of a short circuit, to really fry your P's entire front wiring harness, depending on where the fault occurs.
Most Auto Accessories shops sell in-line fuse holders, which can provide up to 30 amps protection to a wiring system.
I prefer to fit two in-line fuse holders, side by side, to provide power and protection to the headlight relays, and another 30 amp in-line fuse holder for protection of the power supply to the functions and accessories controlled by the ignition switch.
Always fit the fuse holders close to the battery "+" terminal, and ensure that the (heavy) power cables are mounted well away from sharp edges and beat sources.
16: Obviously, if you're going to fit other heavy-current items like electric cooling fans, or road-melting spot lights which are a big drain on your electrical system, you will need to install extra relays and fuses to provide the power and protect your P's wiring system.
Remember when you're planning your wiring modifications that it is entirely likely that at some future time, when you least expect it, one or more of your relays may simply die, so design your new wiring system so that in the event of a fault occurring, you can access your system to fix the fault, without having to strip out the entire dash-board.
I know of one P-nut who went to the trouble of routing all of his P's wiring through channels and sills, etc, and when a serious amount of moisture got into his system and caused major corrosion problems, the only way to restore and guarantee reliability was to strip out most of the "new" wiring, and install a more accessable, standard harness!
I'll continue with this series next month, maybe! If any member has any questions about these wiring mods,
I would be too pleased to offer further assistance.
Please just remember that I am still working weird shift-work hours, but I will return your calls just as soon as it is politely practical!