Ford 7.3 diesel

My SIL has a early 2000? ford 3/4 ton. He has something that draws the batteries down. I went over this afternoon and checked things out. There are 2 solenoids on top of the engine. The back solenoid showed where it has been hot. When I touched 1 of the large wires going to it, the solenoid crumbled. Thought we found the problem, he went to town and got another to replace it. The large wire on the left post still gets hot as something is drawing more power than it needs. What does that solenoid power? Any other suggestions? Thanks............

Glow plug relay and a intake manifold heater relay.

I had an '85 6.9- had 3 different sensors for the glow plugs- all were expensive, most were inaccessable, and all would go out at inopportune times, resulting in glow plugs coming on at 70 MPH on the freeway and frying all the glow plugs. I ended up disconnecting all that sensor foolishness, and putting a 30 amp push button switch in the cab, and hooking it up with 10 guage wire directly to bypass the glow plug sensors and solenoid. Push the button for 10 seconds when truck was cold, and it starts. End of self-frying glow plug problem.

The one in the rear is the glow plug relay and the one in the front is the air inlet heater (AIH) relay.

Ford Diesels through the years all had the same problem with the solenoids... dirty connections lead to high heat ending with crumbling solenoids. Although my 7.3 knowledge ends at 1997, the fix is the same. MAINTENANCE!! You must inspect these connections regularly to avoid the problem you face. Diesels have a sharp, fine vibration that loosens things. Add to that vibration a heavy, stiff electrical cable and you will eventually have trouble. I had a '95 that would wolf a 80.00 glow plug solenoid yearly. In that particular case I mounted the solenoid on a piece of tire so the solenoid could flex with the wires instead of working against them. Also beneficial is Never-Seez on the terminals. The reason the solenoid nuts are rusty is they were overheating, mostly due to a loose connection. Then the rust adds resistance, and more heat. The Never-Seez melts slightly under normal operating temperature, and forms a protective coating on the connection, so if it loosens up,it won't rust right away. Sometimes the solenoid must be removed to service the engine, and Never-Seez saves damage to the solenoid if the nuts get rusty. Regarding the solenoids themselves, I would buy them from Ford. This is not an expensive option when they're properly cared for. If you get them from the auto parts store, they may look the same externally, but they could be circuited differently internally. The wrong wire grounded in an unfused circuit from the powertrain control module will result in way more expense than the cost of an OEM part.

This will get you going.

http://www.ford-trucks.com/forums/790334-gp-and-gpr-system.html

I'm 73 years old and I retired ten years ago, so my memory isn't what it once was, but check with your local dealer about a possible recall on those things. I can't remember if it was a recall, or just warranty repair, but I know the dealership I used to work for, replaced several complete under hood wiring harness on diesels along about then. I still have one that was replaced, I brought it home just to have some wire when I needed it. As I said, I'm not sure, but it may be worth checking into.

What's causing the big draw in amperage through the relay?

During operation it's not unusual for the relays and the wiring to be warm; manifold heaters and glow plugs are heavy draw items. That fried relay was not the problem. If the relays are warm when the truck is not in service, something is energizing the relays. Easiest thing to do is remove the ground cables and install a low draw ammeter between the ground cable and negative post on either battery. Then pull the fuses out of the power distribution box while noting the ammeter reading as each one is pulled. Disconnect all owner added junk before pulling fuses. In many cases they just pick up a hot wire somewhere and it doesn't go through the PDB at all. When the PDB is completely empty of fuses, and there is still a draw, the harness is rubbed raw someplace. If there was any torch work done on the truck, check these areas for melted wires.

Thanks.