More mystery wires in engine bay by firewall

[ScooterDog]

I feel like a broken record, but here I go again...

More mystery wires under the hood by the firewall. Hopefully easy to ID for someone...I hope...

#1 from main harness near brake master - weird clip/plug.



#2 larger cut wire.



#3 back of intake manifold



#4 thru center / top of firewall

 

[midlife]

#1: brake master cylinder/proportioning valve plug

#2: Unknown. Note yellow wire added to main loom!

#3: seat belt relay on left; NSS/backup in middle, and engine gauge feed harness on right top. What's underneath the engine gauge feed harness is very strange, never seen that before.

#4. Unknown.

 

[sdstang]

#1: brake master cylinder/proportioning valve plug

#2: Unknown. Note yellow wire added to main loom!

#3: seat belt relay on left; NSS/backup in middle, and engine gauge feed harness on right top. What's underneath the engine gauge feed harness is very strange, never seen that before.

#4. Unknown.

Midlife

you are one of the greatest contributors to the site!!

 

[ScooterDog]

What's underneath the engine gauge feed harness is very strange, never seen that before.

Do you mean the vacuum tee/lines above the oil pressure sending unit maybe?

 

[red351]

#4 has same marking for the underhood mercury sw lite wire, but the plug end is different.

 

[midlife]

What's underneath the engine gauge feed harness is very strange, never seen that before.

Do you mean the vacuum tee/lines above the oil pressure sending unit maybe?

No. There are some other wires, notably a white/black and a yellow wire into a four pin flat plug?

 

[ScooterDog]

What's underneath the engine gauge feed harness is very strange, never seen that before.

Do you mean the vacuum tee/lines above the oil pressure sending unit maybe?

No. There are some other wires, notably a white/black and a yellow wire into a four pin flat plug?

Oh! That's the repro guage harness.

 

[OMS]

#2 was the aux power wire

Used on cars with high draw power options

convertibles

power window cars

auto seat release system

I think the light group too - under hood, trunk, map, glove box and under dash lights

I think #4 was a wire to the red under dash emission box on 73 cars

 

[eddyw]

#2 was the aux power wire

Used on cars with high draw power options

convertibles

power window cars

auto seat release system

I think the light group too - under hood, trunk, map, glove box and under dash lights

I think #4 was a wire to the red under dash emission box on 73 cars

+1


#2 I think also rear window defrost power supply

 

[rocketmans2k]

Thanks for this info on the #2 pic. Mine hasn't been cut, but I can't find where it goes or where the loom anchors are supposed to connect. It's a good 5.5 feet long and has some kind of resistor or something on the end.

 

[Hemikiller]

That's the auxiliary power feed for options such as rear window defrost, hood light, power windows etc. The wire terminates under the dash with a yellow plug that accepts up to three male bullet connectors. It traverses the engine compartment from the battery (+) post on the starter solenoid, over the shock tower, down the length of the passenger side shock tower brace and then across the firewall, over the driver side shock tower brace and to the grommet. If you lay it along that path, the clips should line up with holes in appropriate sheetmetal pieces.

You can see it by the shocktower in the image below I pulled off the 429 Megasite. Ignore the arrow.

 

[midlife]

That's the power lead for power windows and/or courtesy harness. The boxy thing on the end is a circuit breaker which attaches either to the battery side of the starter solenoid or to the isolation post where the tach-configured headlight harness' alternator lead goes.

 

[rocketmans2k]

Huh...Funny, I don't have power windows or rear window defrost. I'll check the under-dash side and see what's connected there if anything.

Hemikiller, I have tried to lay it in numerous configurations and none of the holes seem to line up. The holes in the passenger brace are already taken by my coil/choke/temp harness. Your instruction and picture were very helpful though, and I found a couple spots I could anchor it to. Now it runs along side my gauge harness on the brace.

Thanks for the quick responses!

 

[Hemikiller]

The coil choke and temp harness should be running along the driver's side of the intake.

That feed was used for power windows, power seat (Cougar), rear window defroster, power top (convertible only) and the automatic seat back latches.

 

[MustangSally44]

Mine had the 2 black plugs same as pic #3 but when I cleaned them up one was actually blue.

 

[rocketmans2k]

The coil choke and temp harness should be running along the driver's side of the intake.

That feed was used for power windows, power seat (Cougar), rear window defroster, power top (convertible only) and the automatic seat back latches.

I'll see if I can find a clean route on the driver's side that allows the temp sensor and choke leads to connect. I have the coil mounted to one of the intake bolts forward of the carb, so the harness might just stay where it is.

I have none of the options listed for this feed, so I think its only purpose is the hood lamp, according to my diagram.

 

[Jerome]

Can anyone tell what color wire go to temp and pressure, coil.73 mustang fastback. Which wire goes to the electric choke

 

[midlife]

Red/green: coil

white/red: oil pressure

red/white: water temp

red/yellow: carb anti-diesel but can be used for choke.

 

[kingb1973]

Been working on my engine feed harness also the last few days. Here is what I THINK I know.

#4 I believe is all emissions related. Brown/Orange Hash may run into the passenger area and connect to a red emissions control. It looks like the connection shown in the upper left of this pic. Not sure if all this is located under dash or in the drivers kick area. Red box is Emissions Control Box?? Note the 2 piece spedo cable that is part of emissions stuff.

My engine feed harness has a place for the wire shown in your pic #4 but I do no have the wire at the firewall. Not used in my setup. 73 emissions seem to be dependent on Engine type, Carb type and Trans type.





My engine feed harness runs along the left valve cover to the front of the block. There are brackets and rings on the cover bolts that keep it in place and off the intake.

Looking at the Repo harness, if I understand correctly, I would use the White/Black wire that is folded back and taped to the harness for electric choke. It gets a 12V feed from the alternator and only when the vehicle is running. The connection for this starts by the start solenoid and is connected with a square connector shown here in the lower right..



I'll get some shots of my harness later today, but gotta go to work to make more money to buy more stuff.