Glow Plugs Always Hot

[BobFunGhoul]

I recently acquired a 1997 Chevy 1500 with a 6.5 and 150,000 on the odometer; purchased as a non running vehicle. The first thing I did was test the glow plugs and found them all to be dead. I replaced all of them and the truck fired up immediately, but I found that the batteries were draining overnight. When I recharged the batteries and reconnected them, I heard the glow plug relay energize and I found 12V at the plugs even when the key is off. I removed the fuse to the relay and still 12V are at the plugs. Where do I go from here? Thank you for your interest.

[jerry598]

Consider a manual glow plug overide setup, available from some of the vendors on TDP.

Others can help you better on this than I can, but I've read somewhere that the glows will burn out quickly when they are on too long. You may need another new set. And be sure to use the up-to-date plugs that will not swell or break. Don't trust the standard over-the-counter plugs. Sorry I don't have anything more constructive to tell you.

[BobFunGhoul]

Thanks Jerry. The truck still starts without hesitation, but I will only run it for a minute or two before I shut it down and disconnect the batteries. Before I go for a new set of plugs I want to correct the problem or look into the manual override that you mentioned. Thanks again.

[oilburnertoo]

Sounds like the contacts are welded together in the glow plug relay. Or some one got creative with the wiring going to the relay and has the ignition terminal to the relay hooked up to battery voltage instead of a switched ignition source. Check the wiring for any obvious splices. Good luck.

[JohnC]

Not sure what you mean by "fuse to the relay", but if you mean the glow plugs are energized with no power to the glow plug relay coil, then yes, the contacts are somehow fused, but, then, it probably wouldn't click...

OTOH, if it clicks on and stays on, then the PCM or the wiring to the relay is at fault. Not sure, but I expect the relay has 12 volts and the PCM provides the ground.

Either way, at least you know why the glow plugs were burned out!

[BobFunGhoul]

John, what I mean by the "fuse to the relay" I'm assuming that the 10A glow plug fuse in the panel under the hood, when disconnected, cuts power to the relay. Is this correct? Whether or not that fuse is installed, there is always 12V to the glow plugs unless the batts are disconnected. When they are reconnected, the relay "clicks". I'll have to get in there to see if anyone had been creative with splicing. Thank you.