Electrical Issues - 84 F250

[ArdWrknTrk]

I'm not sure about '84. The '85 EVTM shows both a pump and a swtching/selector relay.

I think the trailer relay only came with the trailer package.

[grumpin]

swampedout wrote

Its been loud for the 2 years Ive had the truck. It never struck me as a good sign, but it always worked so I never questioned it. Previous owner did tell me the pumps were replaced at some point, although I have reason to question the quality of work they did.

Im going to order some wire this weekend. The Yellow wire running to that relay has some spots where the insulations melted.

Well, that doesn’t sound like it’s going bad like mine, interesting.

[swampedout]

So the relay thats clipped into that housing on the firewall is the Fuel Pump Cutoff. With the Pl/bk wire replaced with a yellow wire.

[swampedout]

Going through the process of elimination, now what is this relay? And where is the other half?
The most distinctive wire is Brown with solid Yellow stripe. And White, Black, Black with Gray stripe.


And for anyone who notices the wire nut in that picture, I am looking at how to address that. Its got the red ignition wire from my MSD box, the large gauge Yellow wire that replaced the PK/Bk into the Fuel Cutoff Relay, and a section of the old PK/Bk wire going into another relay which I think is the Tank Selector Relay? This is the big black and gray relay in the background of that picture.

On that relay, there is also a Orange/Blue striped wire. I used that to search for because it seems uncommon.
On the Color Code it says "238 FUEL SUPPLY PUMP RELAY ORANGE/LT BLUE STRIPE", the only Orange/Blue stripe wire that seems like it would make sense to be tied into those other wires. But I'm not seeing "Fuel Pump Supply Relay" in any of the other documents related to these circuits...

[Gary Lewis]

Well, there are too many questions in that last post for me to get my head around.  Let me try to tackle the easy ones first.

There is not Fuel Pump Supply Relay on our trucks.  Just the Fuel Pump Cutoff Relay, and I guess the thinking was that in an accident it would cut off the pump when the inertia switch "opens on impact".

But when you said "Color Code" I'm guessing you meant you'd searched the listing at Documentation/Electrical/Standard Wire & Color Codes.  Right?  That listing is generic for Ford vehicles of many years and models.  But on our trucks O/LB is used in circuit 238 between the Tank Selector Relay and the Rear Fuel Tank Unit, as shown below on the far right.

[swampedout]

Ah ok. That makes sense. I didnt realize the Color Code Chart was a generic list. I guess it pays to read closely.
I think you answered 1 of 2 big questions in terms of identifying relays.

So the Selector relay and Cutoff Relay are the only relays in the fuel circuit? My last bit of detective work is identifying the green half relay in the picture above

[Gary Lewis]

Trailer Lamps Relay?

You said "Brown with solid Yellow stripe. And White, Black, Black with Gray stripe" but it should be Brown, White w/red dots, Black, and Black w/a White stripe.

[swampedout]

Well Gary, not at all surprising, I think you nailed this one too. The colors do match up, except for an extra wire in there which is Brwn/yellow solid stripe. Could this extra wire be for fog lamps or something?

[Gary Lewis]

It is possible it is for a fog light.  I don't see the wire color shown in the master parts catalog.  But it could be Br/Y.

[swampedout]

I was noticing in the relay chart there were different options for fog lights and I did remove some really old fog lights that were mounted under the front bumper. I assumed they were aftermarket but who knows..

Thanks for your help, Gary. In my research Ive seen so many threads of people asking you "whats this relay." Im sure it gets old, but it really is incredibly helpful.

[Gary Lewis]

Yes, that relay was probably for those fog lights.

And yes, there are lots of questions about the electrical systems, including relays.  These trucks have lots of options for each year as well as changes from year to year.  And, over the almost four decades people have done lots of things to them.  So they are sometimes difficult to figure out.

[swampedout]

I traced the trailer wires back to a connector under the brake booster. Theres a lot of carnage, burnt insulation, exposed wire. Im probably going to replace the connector, relay and all the wiring in between.

[grumpin]

Good find!

I’ve found problems in the trailer wiring on at least two trucks I’ve owned.

[Gary Lewis]

Glad you found it.  Yes, trailer wiring is frequently an issue.

[kramttocs]

Nice sleuthing!
Will echo Dane and Gary. Trailer wiring often falls victim to "do whatever it takes to get it on the road now" when working on the side of the road or last minute trip preparations.

[FuzzFace2]

kramttocs wrote

Nice sleuthing!
Will echo Dane and Gary. Trailer wiring often falls victim to "do whatever it takes to get it on the road now" when working on the side of the road or last minute trip preparations.

That is why I used a Tee that fits between the rail harness and tail light harness that then runs to the 7 pin trailer plug.
I know they dont have the relay but I dont see why I could not add one if I feel I need to?
IIRC it is just for the running lights and nothing else.
I would pull the rear running light wire out of the plug under the booster and add the relay there using the trucks rail harness to still feed the rear & trailer with the Tee.

Then again with a head light relay kit installed removing some of theload off the head light switch would you need to run a relay for the rear lights?
Dave ----

[swampedout]

I like this idea about the Tee, but Im not completely sure where/how you suggest splicing it in.
I was intending on replacing the relay. Theyre cheap and not too hard to wire in. Things can obviously still go wrong but I see no reason not to have it, especially since Im redoing the wires anyways.

Small steps...

[kramttocs]

On the rear cross member, drivers side there is a (likely dirt fused together) plug that connects the rear light harness to the harness that runs along the frame to the front. This goes between those two plug halves.

Depending upon what you will be towing (electrical wise) determines the option I'd choose.

[FuzzFace2]

kramttocs wrote

On the rear cross member, drivers side there is a (likely dirt fused together) plug that connects the rear light harness to the harness that runs along the frame to the front. This goes between those two plug halves.

Depending upon what you will be towing (electrical wise) determines the option I'd choose.

Yep but my Tee has wires coming out that I wired into the trailer connection.
That only dose the lights not the trailer brake wire or a battery charge wire so I had to run them down the frame rail to the connection. I just followed the rail harness down the frame.

It was when I ran the wires that I shorted out the dual tank switch valve wire and wondered why the fuel gauge was not moving on the front tank? It was using gas from the rear but reading the level on the front
Dave ----

[swampedout]

Uh oh. I will try not to short my fuel wires, I have enough problems already.


The good news is I had to leave the truck for almost a full month and got back to it yesterday and it cranked up and held idle for a good while. Ive got one more job for the truck and then I can finally give it some attention.
First thing on the list is fixing the rear brakes.