My glow plug relay on my 1999 f350 is draining my batteries.

A little info on it, I done the switch conversion to the gpr so it could be manually controlled. If I leave the gpr connected it kills my batteries within minutes. The hot post reads correctly at battery voltage, the large post on glow plug side reads 0 whether the switch is activated or not.

The small red wire running to the small post reads at battery voltage when the switch is on.

The small orange wire connected to the other small post reads 3 volts constantly weather switch is on or not. I believe this is my problem area but I'm unsure.

The gpr and switch are both new I replaced them after the problem first occurred and I had the new solenoid tested to be sure it was good. But the gpr is not responding to the switch.


Any help as to what/why my gpr system would be doing this is greatly appreciated. What should i check next?

Thank you in advance.

 

I am not an advocate of switching PCM Commanded functions. I would think that somewhere in your wiring there is a short to another (+) (cross-feeding). This could be just the circuit you’re using to perform the function back feeding. If you’re going to switch a PCM controlled device, switch it on the ground side. That way you’re not interrupting the (+) feed and spiking the component which will in time cause failure. Here are a few excerpts which I hope assist in troubleshooting the issue. If its drawing your batteries down to 0 VDC you've got bigger issues to worry about. Somewhere a wire has chafed or grounded causing 0 Resistance. From your initial test results, it appears your signal wire may be the culprit. Often this occurs in the bundle from the drivers side harness to the fuses panel under the hood.

I would:
1. Disable the switch.
2. Put everything back the way it was originally.
3. See what happens.
4. If all is good, switch the signaling wire to the GPR.

 

0 volts on the Glow Plug side, eh?

Glow Plug Relay coil - this is the "solenoid" that receives power and ground (small posts) to make the relay contacts close - making a connection (big posts) between the battery and the glow plugs.

When the Glow Plug Relay is energized, you have about 10 - 11 volts on both relay contact posts, except when running - then you have about 12 - 13. Once the Glow Plug Relay is off and the engine is running, the battery voltage goes up to about 14 VDC

The PCM energizes the GPR with a ground signal to one side of the coil, and battery voltage is sent to the other side of the coil full time. When the PCM is not sending a ground to the Glow Plug Relay, the control line is "floating" - meaning it will be pulled up to battery voltage through the Glow Plug Relay coil.

• When at rest, the Glow Plug Relay will have battery voltage on the small red wire, the purple/orange wire, and the big black/orange wire on the top post. The other top post (with the white/light green wire) will read ground.
• When energized, the Glow Plug Relay will have battery voltage on the small red wire and both top posts - but the purple/orange wire will read ground

I don't subscribe to putting a switch in a circuit that leads directly to a pin on a PCM. While it makes sense that it should work just fine - I can't pick up a new PCM at Ace Hardware for a few bucks if I damage it. The cost of the PCM is not just the module, there's programming as well.

 

The gpr switch controller only connects to the small post allowing me to operate the glow plugs manually rather than letting the PCM control it. I've never owned a 7.3 or 6.9 without this modification it prolongs the life of the gpr. If I remove the PCM ground from the small post the gpr operates my glow plugs as it should from the switch but if I reattach the PCM ground it drains my batteries.

Also when this issue occurred I had not run my glow plugs it was around 85 degrees that day, I pulled into to work shut the truck off then when I returned 15 minutes later my batteries were completely drained and the gpr solenoid was pretty warm.

Am I going to need to chase the problem through my main wiring harness all the way to thee PCM? What would happen if I bypassed the pcm ground to the gpr and made my own?

Thanks