Power wires to glow plug controller get VERY hot, new controller and wiring harness

crewchief219

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Stumped.. when i bought my truck (92 F250 7.3 IDI) the glow plugs didn't work at all. I replaced all 8 glow plugs with motorcraft, then replaced the controller. In the process I noticed that the ground for the old controller was never hooked up. I finished installing the new controller and it worked great.. so i thought.. well a week later it stopped working so I thought I got a bad controller. I ordered a motorcraft controller and a glow plug wiring harness from an international parts dealer. I replaced both and they worked again but noticed the harness connector below the power steering pump smoking! So after a little looking around I realize it's the two (yellow) glow plug power wires getting really hot. The wiring harness I installed only replaces the wires and fuses going from the controller to the glow plugs, nothing else. So the wires getting hot were never changed.

Here's some additional info.. When i noticed the ground wire for the old controller wasn't hooked up, I also couldn't find where it was supposed to be hooked up.. I wired it to a ground using the same gauge wire (added about 8 inches of wire) Could that be my problem? Where's it supposed to ground?

Also, it's getting hot right out of the fuse box, the closer to the fuses, the hotter the wire is. When I disconnected the harness where it was smoking I noticed a bunch of electrical tape and evidence that this had probably happened before. I'm thinking that's why the ground on the controller wasn't hooked up... just sold it like that.

That's all I can think of at the moment.. STUMPED.
 
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franklin2

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Your system must be different from mine. My two yellow power wires come directly off the large lug on the starter relay mounted on the pass side inner fender. They run down to a plug that is near the A/C box that sticks out at the firewall, and yes they get hot and yes that plug does melt(it's a well known problem) and the best thing to do is cut the yellow wires out of the plug(leave the smaller wires in there if they are ok) and route the wires around the plug. I used 4 crimp ring connectors and bolted the yellow wires together. I am glad I did, because when you do any major work to the engine, it's nice to unplug these wires and move them out of the way to pull valve covers, heads, etc.

The ground wire being longer should not hurt anything. It's just the ground for the "brain" of the controller.
 

crewchief219

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Huh.. think I should run another power wire? Like where yours is? I did run the glow plugs a few times to test the new parts.. that's probably what smoked my harness. Had no idea it would get so hot! This happen to anyone else?
 

OLDBULL8

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If those wires that are getting hot don't have yellow or tan insulation on them, then they are not fusible link wire. They should be 12 AWG fusible link. A ground wire does not carry any current per se, it should be black 16 AWG, there is usually a stud type bolt on the rear of the intake manifold with a nut on it, that's where the ground connection should be.

The wiring harness I installed only replaces the wires and fuses going from the controller to the glow plugs, nothing else. So the wires getting hot were never changed.

There shouldn't be any fuses in the harness going to the glow plugs. The GP harness wires are hooked to the lower end of the zig zag metal resistor.
 
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crewchief219

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They are yellow insulated, should it be getting that hot? Would running another regular wire be a bad idea?
 

typ4

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Ok, back up a bit, the 92 and up moved the wire harness plug to the other side of the truck. 91 and back are on the pass side.
Take those 2 yellow wires out of that multi connector and for now cut and strip them, tie them together with 2 butt connectors, that will solve the heating up problem in that area.
Those stupid pins are not made to handle the amperage of the glow plugs, even though some engineer said it would. Those wires getting hot will fool the controller into acting wierd. so do that and get back to us.
 

gandalf

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The problem sounds familiar. One day my entire glowplug system quit working. This was on the '92 CCLB dually in my sig. On my '92 the glowplug controller was powered from the friver's side. I found that those power wires had melted at the connection. On the instruction from Calvin I cut and capped those yellow wires, and removed them between the connector and the glowplug controller. I then ran a rather heavy yellow cable from the starter solenoid to the glowplug controller. Worked like a charm.;Sweet
 

crewchief219

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galdalf, that's exactly what I just did and it worked great! Typ4 I was going to try your suggestion tomorrow if this didn't work, I'd already bought the cable earlier today so I figured I'd give it a shot and it seems to be a good fix. I used 4 gauge battery cable and ran it from the starter relay to the glow plug controller and no more problems. Oreilly's sold a cable with the right length and connectors... meant to be.. haha. Thanks everyone for the advice! Next: brakes........
 

rlb245

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I don't like to be negative, but if you remove the yellow wires from that circuit you remove all over current protection don't you. With out that protection the circuit could fry every thing. Sounds like a risky fix. Fords engineers are famous for under size gauge wire. Most problem of this type can be resolved by calculating the the current that the system should draw and up sizing the wire to handle it. This is just basic OHM's lay gentlemen. If the circuit is getting that hot there is a high resistance where it shouldn't be. The circuit is on a solid state timer and should be cycling off and on and according to what I read there is some type of thermal regulation in the circuit as well. I had allot of problem with mine when I first got my truck. It required allot of attention. With the wiring being so old. The copper had been heated so much that it was blue and insulation was melted in spot. The terminal connectors were corroded so bad the resistance was 20 ohms. That's a heating element not a connection. So clean it up and replace the bad connections and replace those old britle wires with the proper wire rated to carry that current safely. I'm a journeyman electrician and certified in board level electronics repair. So no of what I speak.
 

typ4

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galdalf, that's exactly what I just did and it worked great! Typ4 I was going to try your suggestion tomorrow if this didn't work, I'd already bought the cable earlier today so I figured I'd give it a shot and it seems to be a good fix. I used 4 gauge battery cable and ran it from the starter relay to the glow plug controller and no more problems. Oreilly's sold a cable with the right length and connectors... meant to be.. haha. Thanks everyone for the advice! Next: brakes........
thats what I did, but I did tie into the original fusible links. I only tell the connector fix because of the validity or rlb"s post, dont want to burn down a truck, I would at least put a 200 amp fuse in the line.
 

crewchief219

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A fuse is definitely a good idea. Sounds like good advice from both of you. rlb245, would a fuse provide the protection you're talking about? And typ4, maybe I'm confused about what the fusible links are. I thought they were after the controller going to the glow plugs, is that wrong? If so all of that is still together. I'm definitely a beginner here and all about learning.
 

franklin2

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The fusible links are located as close as possible to the location where the wire is bolted to the solenoid to protect the wire, as the previous poster knows from his electrical studies, a wire does not protect a circuit, a fuse or fusible link or circuit breaker protects the wiring.

They originally had two fusible links, one protecting each yellow wire. Someone mentioned that later on Ford changed this and ran one large wire, I am not sure about that. But since you now have one large wire, you will have to run one large fuse, or possibly someone knows what size fusible link Ford may have used on the later version that had the one large wire.

I personally like fusible links. They are small and compact and fit in the wiring harness better than a large fuse does.
 

typ4

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There are also fusible links from the controller to the gp wires. The yellows are fusible linked at the starter relay on the 91 and older, not sure on the 92 up. but im sure there are some, they dont pass anything high current over the engine without protection
 

rlb245

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The yellow 16 gauge wire is rated at 20 amps normal current load. But i would like to point out that these fusible links were use in place of a fuse for a reason. All circuit protection is calculated on a current to time curve. That is to say! how long can a fault exist in a circuit before the protection fails. The standard for residential, commercial and industrial are covered by the NEC (National Electrical Code) Well the automotive industry kind of follows this but most there circuit protection in the early years was bassed on the WSA of the wire being used (With Stand Ability). Which was based on the testing done by the American Standards Institute.
Example = a 16 gauge wire is rated at 20 amps at 120 volts DC but has a with stand of 80 amps for 1 hour at 120 v dc. The with stand rating is what the conductor will take before it burns up and fails. So the circuit could fail but it would take a longer time for it to fail. In simple terms the fusible link is a vary long time delay fuse. So if you used a fuse to replace one you should sue the correct amperage rated fuse but make it a time delay or slow blow. If there were to yellow fusible links protecting this circuit then a 40 amp time delay fuse should give you a safe and reliable circuit. I hope I didn't complicate it to much for you. The cars built today follow the NEC electrical standards.
Fusible Links
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0CGcQFjAF&url=http%3A%2F%2Fvintage.mitchell1.com%2FPClubData%2Fchassis%2Fdel74%2FV2D743073.pdf&ei=YWwRUsaLDs6AygHTvoGICg&usg=AFQjCNGAO2o-GHl4yRPYyqD8crQxQvq0HQ&sig2=Op3nh47bDEdyBPIDMNm2uQ
 
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franklin2

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The automotive OEM's definitely do not follow the NEC code for residential and commercial applications. Normal code in most residential applications requires a 12 gauge wire for most 20 amp circuits. It can get complicated with derating for ambient temperatures, the number of conductors, etc. But 12 guage for 20 amps is the general application.

Most of these trucks have anywhere from a 75-100 amp alternator, and Ford never used anything bigger than a 10 gauge wire originally. It is a short run, and as you said there is a time or duty cycle helping the situation out also. I guess they felt generous and put two parallel 10 gauge wires to feed the glowplug circuit, but someone mentioned these wires carry over 100 amps when the glowplugs are working, and they are correct, a 40 amp would not hold it for a second.

If Ford can cut down on the copper being used and save a dollar on each truck, with the millions of trucks they built it adds up.
 
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