Is this harness original and how should I replace it?

[smh00n 87]

So I was chasing an issue with high beam today along with going to put in a horn relay.

Found I had a power supply issue to high beam which I don't fully understand why - possibly the connection through the firewall was a bit suspect.

I stripped back the loom to chase it and wanted to know if this was the original loom. It has the washer hose running through it. The first layer against the wiring was wide black insulation tape, then the bright yellow cloth/gaffer tape and finally another covering of black insulation tape, about 3/8" wide.

I have a fused relay box I can install so was wondering if I should cut up this loom so I can put new wiring in from the relay box. I was thinking of putting it in front of the drivers strut tower (image 2422 just in front of the sticker).

So options are:

1. Hack this harness and replace wiring
   1. What gauge is the original wiring?
2. Buy a new repro replacement harness and hack it splicing in new wire

The connectors won't be original if I replace the wiring but I can add new weatherpack type plugs easy enough.

Or, is there an easier way?

[Midlife 814]

2 hours ago, smh00n said:

So I was chasing an issue with high beam today along with going to put in a horn relay.

Found I had a power supply issue to high beam which I don't fully understand why - possibly the connection through the firewall was a bit suspect.

I stripped back the loom to chase it and wanted to know if this was the original loom. It has the washer hose running through it. The first layer against the wiring was wide black insulation tape, then the bright yellow cloth/gaffer tape and finally another covering of black insulation tape, about 3/8" wide.

The bottom-most layer should be black no-adhesive tape with the washer hose embedded.  Everything above this is after-factory modifications.

[Marauder 1 1]

I've been rebuilding mine for  a while, trying to find a used one with no damage is very difficult.  New ones are over 800.00!   I've found that all the used ones I have purchased been overloaded.  Check the main power connector to see if you see any discoloration around the main power pin.  If you do check under the fuse block for melted wires.  I bought 4 used ones and everyone had some damage in that same spot there.  The wiring for the mustang can not handle to much extra being added.  Halogen headlights are notorious for taking out switches and wiring.

I'm currently wraping mine with some stuff I heard about from a fellow car guy.  It's called cloth loom tape and it's awesome stuff.  Makes for a very nice wrap and no ugly electrical tape adhesive.  You can get it cheap in ebay.

I would also suggest that you purchase the Scott Drake wiring book, best money you can spend.  Believe me trying to figure out that loom on your own is awful,  Also putting a new box on an old harness is no easy task.  The original wiring is not long enough to go through the firewall so it means more splicing.

If your going to rebuild this one the easiest way is to get a piece of plywood and lay this one out on it and tack it down with the tape removed.  Then go wire to wire and inspect the whole thing.  You might find (like I did) wires that were in the tape that are melted together and shorted.  If you need to replace a wire with loom tacked down it's easy to trace and replace.  You can also purchase a pin removal tool if you need to replace pins in the power block and you can also get the proper crimp tool with the original style crimp on pins.  If your wires are bad at the fuse block you can even get new fuse holders to rebuild the fuse block.

Hope that helps.

Mark 

[smh00n 87]

The fuse box is a relay and fuse box, which I was going to put into the loom. My only real option is to cut the harness and run the original headlight and horn wires into the relays, then all new wiring from the relay box to the headlights and horn. The new box will be on the drivers inner guard.

I'm not keen to cut into this loom as it seems to be good. I have previously pulled the original fuse box and not seen any issues there and theres no other wiring issues on the loom except for dull headlights and horns that are very sick.

I need to run relays to the headlights as I have halogen lights and I figure replacing the wiring to thicker core will only future proof it.

70 Mustangs are not common over here so even finding a used harness would be hard let alone one I could hack up. If one of your looms has dud headlight and horn wiring but good elsewhere I could make use of one :)

[danno 128]

From my investigations about the horn, the problem is usually in the steering column. It might have poor connections between the turn signal switch and steering wheel, and poor connections in the horn switch.  I do not think it is the wires ( although it could be).   The solution is to add a horn relay, just like the headlight relay.  

If your original harness is good, I would not hack into it. The headlight and horn relays can be added as  additional harnesses.