Ignition Switch RUN terminal wire R/LG always hot

[Lawrence Koepke]

A real mystery. My 1991 F350 7.3 IDI wouldn't turn off with the key, so I did the usual and pulled the FSS wire to kill it. I replaced the Ignition switch and checked the actuator rod. I checked voltages on the switch and found the RUN R/LG wire was hot. This wire is supposed to get voltage from the switch, not supply it! I pulled the connector from the alternator, in case it was backfeeding the voltage; still hot. I pulled the R/LG wire from the glow plug controller; still hot at the IGN SW connector. I pulled the TECA power relay, R/LG hot there too, and still at the IGN SW. I pulled the fuses connected to this circuit, no luck there. I'm running out of ideas. What else can be the source of 12 volts to this circuit, other than the IGN SW? I figure it must be back-fed from somewhere, but it's not the alternator, glow plug relay, TECA relay or the fuse box.

 

[franklin2]

You are doing the right things. Look for any added non-stock wiring. Also look at the *** of wires going over the pass side valve cover to the plug there. That is where the large glowplug wires run to feed the glowplug relay along with a bunch of smaller wires. These wires like to melt the plug. It may have melted against the ignition wire and shorted the glowplug power wire to the ignition wire. This melted plug is usually very near the A/C box on the pass side.

 

[Farmer Rock]

I don't know if this could be related or not, but it's worth mentioning. I recently replaced a GP relay, and installed all the wires correctly but the truck wouldn't shut off afterwards. I took a close look again at the relay, and noticed one of the terminal rings was just barely touching the hot terminal on the relay, due to the end not being insulated. It was back feeding the ignition wiring.I fixed that, and it shut right off.



Rock

 

[IDIBRONCO]

Lawrence Koepke, did this just suddenly start happening? When you said that you replaced the ignition switch, did you replace the key switch by the steering wheel or the actual ignition switch down toward the bottom of the steering column? It's possible that something's jumping power across to this wire at the actual ignition switch.

 

[Lawrence Koepke]

I replaced the switch down toward the bottom of the steering column, but I have never tried it, because the R/LG wire (RUN) should not have 12 volts on it when the connector is not connected to the ignition switch. The wire next to it, BR/PNK (I think), is also sitting at 12 volts

 

[ifrythings]

These may help.

You must be registered for see images attach

You must be registered for see images attach

 

[Lawrence Koepke]

To all who posted, a big hearty Thank You!

I finally found the culprit, in the harness right where Franklin2 suggested. One of the glow plug wires feeding the relay had gotten hot enough to melt insulation on itself and a blue wire next to it, and I suspect the blue wire is the FSS solenoid wire, as it was backfeeding 12 VDC throughout the entire ignition circuit. This glow plug was not the factory wire, as I had replaced the two wires feeding the Glow Plug Relay from the harness connector to the relay with 10 AWG automotive wire after the pins in the connector had gotten hot enough to melt the connector, as well as some insulation. I figured I was safe with the 10 AWG, as it is heavier than the factory wire. I'm wondering if the 30 year old glow plugs (but only 90 K miles) have increased in resistance sufficient to draw enough extra current to over-burden the wires. I have ordered new ZD-9 glow plugs and a new Duralast glow plug relay, as the relay cycled a number of times before giving up the ghost after I fixed everything, and the Wait To Start light never came on. I also will buy new batteries, as this was the last straw for them. I have learned that 12 VDC on the ignition circuit of these trucks for 12 hours can damage a fair amount of stuff!

BTW, is there anything special I need to know to get old glow plugs out, and the relay? If so, I'm all ears (or eyes, as the case is).

 

[Farmer Rock]

To all who posted, a big hearty Thank You!

I finally found the culprit, in the harness right where Franklin2 suggested. One of the glow plug wires feeding the relay had gotten hot enough to melt insulation on itself and a blue wire next to it, and I suspect the blue wire is the FSS solenoid wire, as it was backfeeding 12 VDC throughout the entire ignition circuit. This glow plug was not the factory wire, as I had replaced the two wires feeding the Glow Plug Relay from the harness connector to the relay with 10 AWG automotive wire after the pins in the connector had gotten hot enough to melt the connector, as well as some insulation. I figured I was safe with the 10 AWG, as it is heavier than the factory wire. I'm wondering if the 30 year old glow plugs (but only 90 K miles) have increased in resistance sufficient to draw enough extra current to over-burden the wires. I have ordered new ZD-9 glow plugs and a new Duralast glow plug relay, as the relay cycled a number of times before giving up the ghost after I fixed everything, and the Wait To Start light never came on. I also will buy new batteries, as this was the last straw for them. I have learned that 12 VDC on the ignition circuit of these trucks for 12 hours can damage a fair amount of stuff!

BTW, is there anything special I need to know to get old glow plugs out, and the relay? If so, I'm all ears (or eyes, as the case is).

As long as ZD9s are in there now, it should be pretty straight forward to remove them, but I always soak them in penetrating oil at least 1 day in advance to be safe. Swapping out the relay is just as simple, just make sure to put the wires on the correct terminal when installing the new one.



Rock

 

[Lawrence Koepke]

Thanks for the tips. BTW, I had replaced those glow plug relay feed wires so many years ago, I had pretty well forgotten about it. I'm wondering what to replace them with so I don't go through this again. I thought AWG 10 automotive wire would be sufficient. Do others have this problem with these wires and connector pins for glow plug relay wires?

 

[laserjock]

That’s a common issue with the connector. A maxi type fuse (150 or 175 amp) and a single 4 AWG will probably do it just fine. I actually relocated to my controller to my fender and ran an Anderson style connector over to the harness.

 

[franklin2]

I thought the factory used two 10 gauge wires to feed the glowplug circuit? With two separate fusible links. Like the previous poster mentioned, I think I would replace this glowplug feed all the way back to the starter relay on the fender where it comes from.

You can get universal #6 and #4 battery cable wires at the store. Not sure if they are long enough. Just make sure you get a large fuse like he mentioned also. This is a very large wire hooked directly to the batteries, so you don't want it to start a fire.

 

[Lawrence Koepke]

I have read that the glow plugs can draw up to 200 amps, but laserjack suggests a 150 or 175 amp fuse will suffice. I'm thinking he may know from experience. How many amps do the glow plugs draw? I'd test the draw at my relay, but it's dead. I'm heading to the parts store to get a new relay, and glow plugs, and will want to put in the correct fuse. Any thoughts on fuse vs. breaker? I installed breakers that reset when I installed new trailer wiring, and that seems like a nice way to go... except perhaps in hard short, I reckon one of those breakers will cycle forever, yes?

 

[Philip1]

I have read that the glow plugs can draw up to 200 amps, but laserjack suggests a 150 or 175 amp fuse will suffice. I'm thinking he may know from experience. How many amps do the glow plugs draw? I'd test the draw at my relay, but it's dead. I'm heading to the parts store to get a new relay, and glow plugs, and will want to put in the correct fuse. Any thoughts on fuse vs. breaker? I installed breakers that reset when I installed new trailer wiring, and that seems like a nice way to go... except perhaps in hard short, I reckon one of those breakers will cycle forever, yes?

When I was testing my glowplug amp draw (when warm outside) it spiked around 260-270amps and quickly dropped off. So I decided to use a 250 amp breaker with no issue. However when it got cold it would pop the 250a breaker every cycle so I replaced it with a 300amp and have had no issues since.

 

[Lawrence Koepke]

laserjack, I see you have the Banks turbo. I received mine on Friday, and it will be the next project after I take care of this current issue. I'm wondering if I should move my relay/controller like you did. I have not seen one of these trucks with the Banks Sidewinder installed, but I have to think that it will make the GP relay/controller even more difficult to service. Would you advise moving the relay, considering the Banks, or will I still be able to service it? In fact, do you, or anybody, have any idea why Ford chose to install it in the location they did, at the rear of the intake manifold, making it hard to reach?

 

[IDIBRONCO]

Wasn't the controller location an International thing? Ford just used the same location? When I get to working on my 1987 with the 7.3 style controller, I'm going to relocate mine similar to what Laserjock did. For me, it's not so much for servicing it, but more for the longevity of all of the related parts. The turbo puts a lot of heat into everything back there. It will make the wiring brittle as well. I'll also be going to a manual control so that will help the longevity of the glow plugs. I'm not trying to reinvent the wheel, just move it to a different location and put a fancy rim on it at the same time.