Heya, still gathering as much info as I can about my project truck. (loved the 33 page GP super tuning diatribe btw). I went to the stealership today to find out if they carry the engine bay wiring harness anymore (nope, none on the radar except 1 in Ohio, I'm in California). Since diesel owners are kind of fanatic about their trucks; and only 39% of fords hit the road with IDI's, I'm pretty screwed if I have to find an intact truck at a pick-n-pull.

I was told that the company "Helm Inc." printed all the manuals for the shop technicians. I looked up Helm manuals and they do not print a manual of the wiring diagram for trucks between 1983 to 1986 (1984 & '85 return no results). Since my truck is an '85, which manual should I go with, up or down a year? I figure $12 is a fair starting point for rewiring my engine bay.

On a second note, I looked through Summit Racing online and found Painless electrical connectors starting around $12, then went to RadioShack online and found (what looks like the exact same connectors) for about $4.80 a set. Anybody know the difference (besides $7.20, ha ha).

As soon as I get a digital camera that works I'll post some pics of the nightmare that I'm looking at under the hood. I'll need a lot of help sorting it out. Thanks in advance.

 

I would think the 85 and 86 years are closer, I know when it comes to the fuel gauges, they are the same, so it would seem that engine harness wiring should also be the same. Near as I can tell, engine wise, the harness is the same between 84 and 86, judging by my 86 and my dad's 2 84's.

 

Thanks fellro86 for your response. I went pick-n-pull hopping today looking for diesel trucks, the ones I found were pretty well picked through, and until today I didn't know Atilla the Hun drove a ford, but I could sure see his handiwork in every salvage f-250. Wiring torn, cut, torched, and otherwise unusable.

The only truck I came across that might have worked was a 1991 f-250 w/7.3L IDI. Next newbie question, "How different are the '85 and '91 wiring harnesses forward of the firewall?" I know they use a different glowplug harness, and probably a 10amp larger alternator, other than that, can I get a '91 harness to work in my '85 truck?

Also, Pick-N-Pull has all complete engine assy's listed for $200! I asked about the diesels, they said "all engines are the same price." Now, if only my truck worked so I could go get a new engine. Damn catch 22s anyway! Thanks

 

It's essentially the same motor, with the same sensor locations, so I would think it is the same for the most part.

 

Well I started gathering info today from a good site.....but I ran out of time before I had personal business to conduct... The systems are more detailed on the 86 and the info is confusing to me as I was under the impression the 7.3 info would be relevant to the 87 but is included in the 86 info......?????? So I have to complete the task next week 26th earliest. I will forward what I have already when it is scanned...

 

probly the reason is the early 87s were built in 86

 

I actually found my 86 info buried in my files.....but they are very different from the new one's I was compiling today......

mejonz
Most new year trucks are listed by that year regardless of when they are built....... so I will persue this a little more next week.

 

I was thinking I guess more along the lines of the production date verses the model year

 

This diagram is supposed to be for the "83 to 86" diesel trucks.

 

franklin2, thanx so much for that diagram. it will really help, and it is very clear (easy for us non-electrical types to follow). Happy holidays everyone!

 

well, I was able to spend a couple hours with the truck today. what a nightmare! I was able to get all the glow plugs out (ac delco's, thankfully no broken tips). I checked them for resistance, all of them had no reading the last 1/2 to 5/8ths of an inch from the tip, but would register 0.01+ ohms closer to the threading. does this mean that they are burned out, no ohms at tip? After replacing all the Glow Plugs with zd1a's the GP light finally came on. Next time I work on the truck I will use the mv setting on my multimeter to check if they are heating up at all.

The glow plug controller was replaced with something, no idea what. I don't know what the PO was trying to fix, but I don't think there is an intact line on the vehicle! CRAP!

One of the more disgusting poo-piles is located on the passenger side wheel well under the power relay (lower left corner in the diagram) HAD a connector with 4 or 6 wires, and plugged into something that has two threaded posts next to the 4-6 pin connector. Sorry I can't be more accurate, but I havn't a clue what it is. it is right next to the square motorcraft metal box with a plug in connector (again, don't know what it is). anyway, it isn't a clip in connector anymore, only 3 of the wires are still there, with female spade connectors, and are held together with silicon glue. (that's the same story with the glow plug controller on the driverside rear of the engine).

Anybody in the Bay Area who has any idea what the wiring should look like and would be willing to look over the truck with me for a while? Help.

 

Many of the 86 and earlier glow plug controllers caused the glow plugs to come ON when it failed.
This would burn the glow plugs up in a very short amount of time.

Just a very few years ago, a replacement controller was in the 150 plus price range, but they are getting much cheaper now.

The main difference in wiring harnesses on 86 and earlier trucks versus 87 and newer trucks was the glow plug system and the connector where they plug together.
87 had the glow plug controller/relay mounted on the intake manifold.
The 86 had the controller mounted on the head, relay was on the inner fender.
86 had the fuel heater wrapped around the fuel line from the lift pump to the fuel filter.
87 had the fuel heater in the filter header.
86 water seperator was mounted on the firewall.
87 had it in the fuel filter.
86 had no filter restriction sensor
87 did have one

The newer style 87 and later harness conncetor has more positions than the 86 and earlier connector, so they will not plug into each other.

Off the top of my head, I think there are two more wires on the new style harness, one for the water in fuel sensor and one for the filter restriction sensor.
Several of the harness colors changed from the old style harness to the new style.
Another difference with the glow plug system is the 87 and newer had battery power running through the engine harness, on the 86 the engine harness only had battery power in the engine harness when the glow plugs were heating.

It only takes a little bit to make the changes required, but you have to splice wires instead of just plugging the harness together.

On the 86 and earlier trucks the glow plug relay was a power distribution point as well as the starter solenoid, so that is why there are so many wires on the battery terminal of the glow plug relay.
Some had more wires on the glow plug relay, some had more on the starter relay.
On the 87, the glow plug relay was mounted on the engine, so all the power wires moved to the starter relay as the main power distribution point.

The flat rectangular box with the connector is the voltage regulator, five wires in the connector if I remember right.

86 and earlire glow plug relay


87 and later glow plug relay/controller

 

Dave, thanks for the detailed info and pictures. On my relay there is a red wire with a red cap where your picture shows "controller terminal" (the post is slightly larger than the one on the bottom). The ground terminal is disconnected since the wires it is connected too are cut and spliced into something else (that mystery box with two posts and the 6 pin connector).

On the back of the engine, on the drivers side of the block, I think the PO removed the glow plug controller and replaced it with a GM/Chevy glow plug controller (two male spade connectors). Anybody every heard of this?

I hope to get a digital camera for Christmas so I can take pictures of the project to help me explain what i'm looking at.

 

Sounds like you have your work cut out for you.

The original glow plug solenoid will not work if the ground wire is not there.
The ground wire completes the coil circuit to energise the relay.

There is a possibility the original relay was replaced with a starter relay, they pick up a ground through the mounting bolts if they are mounted on a grounded surface.

Pictures would help, but there will still be a ton of questions needed to figure out what is happening.

 

well, I seem to have made a bad problem worse. today while working on the truck I replaced the 540 cca marine battery with an 875 cca wally-world special, then connected the black ground terminal with the 90 degree boot (lower post on the glow plug relay picture) back up again. After figuring out that the PO or relative put something other than diesel in the rear tank, I drained both filters (and not having new ones immediately available . . . I know! I'll buy some new filters once the wiring is working) and had a friend help purge the air from the system, I got ready to start the truck and plugged all the wiring back in (now ground terminal was included) and ran the truck through a glow plug cycle . . . no problems, another glow plug cycle and cranked it over . . .


HOLY CRAP, SMOKE! The ground terminal wire overheated, burned the sheath off and melted through some other wire sheathing! I quickly took it off the terminal, but the starter was still turning, so I took the negative leads off the batteries to get the starter to stop spinning. When I tried to put the neg lead back on the battery, the starter engaged. There is a constant ground somewhere in the wiring causing the starter to operate without the key in the ignition or the switch turned.

(Anybody know a good insurance company who won't ask too many questions about a vehicle fire? Thinking I'll break even with a "total loss" if it catches fire 'mysteriously'.)

I put an ad on craigslist looking for a wiring harness. One wrecking yard already e-mailed me. I'm thinking about cutting and splicing the wires inside the cab under the dash. How difficult is it to run a complete wiring harness rather than fix a section?

Another few questions: does the after-glow relay have a clip connector with 4 wires and two posts, one of which connects to the pos lead of the battery?secondly, if the gp relay was replaced with a starter solinoid, would that explain why the ground terminal wire fried? lastly, what are some suggestions about the starter's auto-engaging problem?

I got some pics today, but I don't think they are relivant anymore. thanx