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Random ground pigtail on Firewall

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JMUBullnose

Random ground pigtail on Firewall

Hello folks - me again...

Just remembered this after driving in Old Red today. (FYI - think I'm happy with the shifting, now think I have a misfire situation!)

However, when I was last under the hood I noticed a random disconnected pigtail on the drivers side firewall, directly behind the valve covers. Anyone know what this should have connected to?

1984 F-150, 302 CID (5.0 L) Windsor V8, 2 BBL carb, power windows added, remote entry added. AC. Automatic Transmission.

Gary Lewis

Re: Random ground pigtail on Firewall

Administrator

Glad you are making progress. These trucks are like onions - we keep peeling the layers and crying, but it is all good if you like onion rings.

As for the pigtail, it doesn't look like a Ford connector. But, there should be a ground from the engine, usually from the valve cover bolt to the wiper motor. Do you have that ground?

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

JMUBullnose

Re: Random ground pigtail on Firewall

Hmm, I'll have to look when I go back out there at lunch time.

I guess I'll be replacing plugs and wires this weekend (have had them sitting on the shelf for a bit!). Hopefully that helps with the misfire...it definitely presents itself once the engine is warmed up.

1984 F-150, 302 CID (5.0 L) Windsor V8, 2 BBL carb, power windows added, remote entry added. AC. Automatic Transmission.

Rembrant

Re: Random ground pigtail on Firewall

In reply to this post by JMUBullnose

JMUBullnose wrote

However, when I was last under the hood I noticed a random disconnected pigtail on the drivers side firewall, directly behind the valve covers. Anyone know what this should have connected to?

That very same plug is hanging on the firewall of my 1984, also not connected to anything. It never was on my truck. Ford just used a generic ground cable I'd guess, and it was unused on some models. Maybe it was used on the trucks with the EEC-IV or whatever it is called?

Gary, it is part of the engine ground cable. The unused pigtail is crimped in the firewall end connector of the engine ground cable. The engine end of the cable I believe goes under one of the screws that attach the throttle bracket to the intake manifold.

1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

JMUBullnose

Re: Random ground pigtail on Firewall

Rembrant wrote

That very same plug is hanging on the firewall of my 1984, also not connected to anything. It never was on my truck. Ford just used a generic ground cable I'd guess, and it was unused on some models. Maybe it was used on the trucks with the EEC-IV or whatever it is called?

Funny enough I was just wondering about the whole EEC-IV thing - what's the differences? I was looking at new distributor caps and rotors while puzzling the misfire issue and saw some of the kits called out specifically EEC & non-EEC and I have no clue which I have.

1984 F-150, 302 CID (5.0 L) Windsor V8, 2 BBL carb, power windows added, remote entry added. AC. Automatic Transmission.

Rembrant

Re: Random ground pigtail on Firewall

JMUBullnose wrote

Funny enough I was just wondering about the whole EEC-IV thing - what's the differences? I was looking at new distributor caps and rotors while puzzling the misfire issue and saw some of the kits called out specifically EEC & non-EEC and I have no clue which I have.

I believe the quickest visual clue is whether you have vacuum advance on your distributor or not. If you have a vacuum advance line, then your truck is Duraspark II, not EEC-IV. No vacuum advance, then you have an electronic distributor and feedback carb (EEC-IV).

The second bit of evidence, as shown in your picture, is that big black rubber plug in the firewall right next to where the unused pigtail is. If your truck was EEC-IV, then there would be a bundle of wires going through the firewall where that plug is, to the ECU in the cab.

Somebody can correct me if I'm wrong here, but that is my understanding of the quick and dirty checks as to EEC-IV and non EEC-IV. I think there is a a bit of a misconception that all 1984 trucks were EEC-IV. Maybe it was a mid-year change, I dunno, but my 1984 is not EEC-IV, and it doesn't look like yours is either. I've found others in my searches as well. My truck was a one owner unmodified vehicle, so it came from Ford that way.

As always, take it all with a grain of salt. I'm certainly no expert, but I did go through all this originally when ordering parts for my '84 F150.

Gary Lewis

Re: Random ground pigtail on Firewall

Administrator

I think you are right on that. Good points.

As for the ground, I'm glad to know that. Thanks!

Gary, AKA "Gary fellow": Profile

NotEnoughTrucks

Re: Random ground pigtail on Firewall

In reply to this post by JMUBullnose

Well, unless you have that feedback carburetor thingy, you won't have EECIV in your 84 F150.

I think that pigtail may be the power for the underhood light.

ctubutis

Re: Random ground pigtail on Firewall

NotEnoughTrucks wrote

Well, unless you have that feedback carburetor thingy, you won't have EECIV in your 84 F150.
^True
I think that pigtail may be the power for the underhood light.

Bingo! Light green/yellow-stripe, 15A fused, always-on power for optional underhood lamp.

Rembrant

Re: Random ground pigtail on Firewall

In reply to this post by NotEnoughTrucks

NotEnoughTrucks wrote

I think that pigtail may be the power for the underhood light.

It's an unused ground. Here's a little clearer view of it on my truck. Easier to see with no engine;).
It is crimped in the firewall end of the engine ground cable.

Gary Lewis

Re: Random ground pigtail on Firewall

Administrator

I found some interesting information here: Electrical/Grounds/Engine To Firewall Ground.

Gary, AKA "Gary fellow": Profile

Rembrant

Re: Random ground pigtail on Firewall

Gary Lewis wrote

I found some interesting information here: Electrical/Grounds/Engine To Firewall Ground.

Well ain't that slick. You are SUCH a keener Gary! So then...what is the "ECA" used on some trucks? Is this something in the EEC-IV system?

Gary Lewis

Re: Random ground pigtail on Firewall

Administrator

ECA means Electronic Control Assembly. The computer for the EEC (Electronic Engine Control) is called an ECA, while the whole system is called EEC-III, or EEC-IV, or ..... You can see that here: http://www.garysgaragemahal.com/electronic-engine-control.html

Gary, AKA "Gary fellow": Profile