Ford F150 Forum - Community of Ford Truck Fans - Electrical

88 F150 5.0 Rough Running and Stalling

tom.metge — Thu, 04 Jun 2026 16:16:46 GMT

Hello everyone,

A week ago my truck stalled without warning, as if someone just took the key out. Pulled over and it started right back up. That's happened a few more times since then.

I replaced the TFI module thinking that would do the trick, but it's only seemed to get worse. A couple days ago it stalled and I had to wait a few minutes before it started again. Yesterday it ran great with no problems, and then on my way to work today it started to get really bad. The engine seemed to cut in and out as I was driving, getting me really concerned for a while. It was bucking me around. It never fully cut out, but it was definitely worse at higher RPMs. It doesn't seem to happen when the truck is idling.

Any thoughts or suggestions? Not actually sure this is an electrical problem but I think it is

Part id and info?

Nicholas Austin — Wed, 03 Jun 2026 00:08:42 GMT

I was told this part is the most likely cause of my random shutdown issue but i forgot what its called and cant find my repair manual

Code extraction

dhoskins18 — Fri, 29 May 2026 18:28:55 GMT

I have been trying to get codes out of my new computer but I have been told 3 different ways and I do not want to trash the new computer,if someone could show a diagram of the process and a pic of where the ends of a jumper go,I hope I can get codes from it.Been told to use a multimeter, jump 1 wire to the battery but none said consistently where the other end goes,1 said eec, where ever that is,the other said the large portion the plug, so I need something difinitive please,have tried searching here but it gave me the voltmeter way,I don't have 1.So any help will be appreciated Thank You.Dave H.

1991 F-150 5.0 bad fuel pump relay

dhoskins18 — Fri, 29 May 2026 18:06:04 GMT

I have a bad fuel pump relay, but the problem is,there are only 5 prong relays for sale, so how do you get a fuel pump relay for my truck? I checked the resistance and it was sorta close to the ok specs, but missed by 6.8 , so it needs replaced but I cannot find 1,does anyone have any ideas? I
All help will be greatly appreciated.Thank you.Dave H.
BTW I need a 4 prong fuel pump relay for my truck, and Ford does not make them anymore! Discontinued.

1991 F-150 5.0 vacuum line under hood diagram needed

dhoskins18 — Thu, 28 May 2026 17:34:37 GMT

I have replaced many things on this truck, some by people on here, some by the outputs of a bad computer, 4 bad fuel pumps later and am no better place,I found out that B4 I got the truck back the vacuum lines had been messed with by my brother's friend, non mechanic,and I do not know if they are correct and I just found out that my truck DOES have a fuel pump relay, after asking on here and getting no answers, I've wasted much cash I really shouldn't have spent, but it has sat for al.ost 20 years,so it has needed many things,but I am still back to same problem, no supposed fuel pressure, it has it at first but for only a split second then it goes to zero, I just replaced the front tank as it was so rusted at the fp mounting hole that the ring would not completely seal it and it had deep pit marks of rust, so new tank.Now this fuel pump is not sending the gauge any info on how full it is, ,I am just about to call the scrapper! I really need help not jokes, remarks on how it can't be I need to know why it is doing what it is.Ford mechanics are stumped as they haven't seen a truck this old, and don't want to work on it.Im 2k I to this in parts, there isn't much left ! So can it be vacuum, a relay, or what,I really need an up close pic of a 91 5.0 f-150 vacuum routing ,as my diagram is unreadable, and I cannot understand abreviations on pics Thanks,Dave H.

Third brake light terminal

fork off — Wed, 27 May 2026 15:15:55 GMT

Hi does any one happen to know where you can get these

3rd Brake light Bulbs

fork off — Mon, 25 May 2026 14:40:06 GMT

Hi Can you change 3rd brake light bulb from 921 to 168 to stop plastic melting with out effecting E4OD 4.9 Automatic transmission

3rd Brake light pig Tail

fork off — Fri, 22 May 2026 15:32:34 GMT

Hi I have burnt out 3rd brake light sockets so I have purchased replacement from Bronco Graveyard one of the old sockets has 3 wires coming out of it all the replacement sockets have only 2 wires. Can some one please tell me how to connect this .
Thank you

1994 f150 4.9

91 F-150 low pressure

dhoskins18 — Tue, 19 May 2026 23:52:36 GMT

I have a video showing my truck running with 0 pressure on the harbor freight gauge, new filter and new pump, it runs but will stall but it has 0 pressure , the schrader valve when you connect to it let's out a small amount of gas but no pressure behind it.Is there anything else other than the pump? Thanks Dave H. I need alot of help!

1991 F-150 5.0 upper intake bad gasket

dhoskins18 — Sun, 10 May 2026 21:04:46 GMT

I took the upper intake off to check injectors and wiring due to while running brake cleaner under the intake would make it pick up the idle,so I removed the upper intake and by the back cylinder I noticed quite a bit of oil coming out of the intake onto my floor after I took it off! Is this normal? I just replaced the pcv valve but I cannot get this thing to run normally.Someone told me an eirthia switch can cause havoc in these trucks,I cannot find a thing about them or what happens when bad! Any help will greatly appreciated as I've put a fortune in this and it won't stay running , runs for a short time then starts acting like it's out of gas or has an electric problem! I need a mechanic! Thanks again Dave H

88 F150 Rear Right Blinker/Taillight/Hazards not working

tom.metge — Sun, 10 May 2026 18:33:55 GMT

Hi all,

Been chasing this problem for a while now. A while ago, my rear left blinker and brake light stopped working. At this point all the hazards worked. After some research, I replaced the multifunction switch in the steering column. After replacement, the left blinker/brake light worked, but the RIGHT side stopped working.

Eventually I figured I just got a faulty switch, so I replaced it with a nicer one. That seemed to fix the problem� temporarily. After a couple days I�m experiencing the same issues.

so here�s what it does now: all lights work except the rear right brake light, blinker, and hazard. The running light does turn on when I turn the headlights on, which is the same wire and bulb.

Anybody have experience with this?