7.3 Powerstroke Glow Plug Kit

Why Does Your 7.3 Powerstroke Need a Glow Plug Kit?

Cold Starts Get Harder as the System Ages

The 7.3's glow plug system has one job: heating the cylinders so the engine lights off cold, and every component in it degrades together. Plugs erode, relay contacts pit and stick, controllers drift, and the truck that started at 10 degrees now cranks forever, blows white smoke, and idles rough until it warms up. Those are the textbook symptoms of a glow plug chain on its way out.

The Under-Valve-Cover Harness Is the Hidden Failure Point

Ford routed the glow plug and injector wiring through harnesses molded into the valve cover gaskets, and under years of heat cycling, those internal connections burn. A single melted pin kills the glow plugs on one bank and often an injector circuit with it, which shows up as a cold misfire that smooths out warm, plus codes the truck throws every morning. Replacing plugs alone leaves the burnt harness in place to eat the new ones.

Failed Plugs Take the Harness With Them

A glow plug at the end of its life can short and overheat, and the extra current melts the surrounding harness and connector, sometimes welding itself to the injector wiring. What started as one weak plug becomes a no-start truck needing gaskets, harnesses, and a relay. That cascade is exactly why we sell the system as a kit instead of pieces.

What Can a Glow Plug Kit Solve?

New Harness-Gaskets Restore the Whole Circuit

The heart of every kit is the high-temperature valve cover gasket with its integrated under-valve-cover harness and fresh OEM-grade connectors. Sealed against oil and heat, the new harness feeds all eight cylinders evenly and stops the burnt-connector misfires for good. Both generations are covered: the 1994-1997 OBS gaskets cross to F4TZ-9D930-K, and the 1998-2003 Super Duty gaskets cross to F4TZ-12A342-BA.

Heavy-Duty Relay Solenoids and Controllers

Every kit includes a heavy-duty relay solenoid with contacts sized for the sustained current of a full glow cycle, and controller-inclusive versions add the glow plug control module for trucks whose module has stopped talking to the PCM. Together they restore full key-on glow timing and the post-start glow that keeps cold idle smooth.

Complete Kits With Glow Plugs Included

Select kits bundle new glow plugs with the gaskets and harnesses, so a full cold-start overhaul lands in one box. Fresh plugs, fresh wiring to feed them, fresh relay to switch them, one evening in the driveway, and the truck starts like it did in 1999.

Shop 7.3 Powerstroke Glow Plug Kit by Ford Truck Engine & Fitment Guide

• Glow Plug Harness, Gasket, Relay & Controller Kit (1994-1997 OBS) - Fits the 7.3L Powerstroke in Ford F-250/F-350 OBS body trucks (1994-1997). The complete cold-start overhaul for the OBS era: harness, gaskets, relay solenoid, and control module in one package.
• Glow Plug Harness, Gasket & Relay Kit (1994-1997 OBS) - Fits the 7.3L Powerstroke in Ford F-250/F-350 OBS trucks (1994-1997). Crosses to F4TZ12A342-BA, F4TZ-9D930-K, F4TZ-6584-A, and F81Z-12B533-AC; harness, gaskets, and relay for trucks with a healthy controller.
• Valve Cover Gaskets, Harnesses & Glow Plugs (1994-1997 OBS) - Fits the 7.3L Powerstroke in Ford F-250/F-350 OBS trucks (1994-1997). Harness gaskets with new glow plugs included; the right kit when the plugs and wiring are due together; crosses to F4TZ-9D930-K.
• Glow Plug Harness, Gasket, Relay & Controller Kit (1998-2003 Super Duty) - Fits the 7.3L Powerstroke in Ford F-250/F-350 Super Duty trucks (1998-2003). The complete kit for the Super Duty era, covering the 1999 through 2003 trucks that make up most of the fleet.
• Glow Plug Harness, Gasket & Relay Kit (1998-2003 Super Duty) - Fits the 7.3L Powerstroke in Ford F-250/F-350 Super Duty trucks (1998-2003). Harness gaskets plus heavy-duty relay for trucks whose controller is still working.
• Valve Cover Gaskets, Harnesses & Glow Plugs (1998-2003 Super Duty) - Fits the 7.3L Powerstroke in Ford F-250/F-350 Super Duty trucks (1998-2003). Harness gaskets with glow plugs included, crossing to F4TZ-12A342-BA for the Super Duty valve covers.

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Related 7.3 Powerstroke Collections

Build out the rest of your 7.3 with the full platform catalog:

• 7.3 Powerstroke engine upgrades - The complete performance parts shelf for the 7.3 Powerstroke, from airflow to oil system hardware.

FAQs About 7.3 Powerstroke Glow Plug Kit

What are the symptoms of bad glow plugs on a 7.3 Powerstroke?

The classics: hard starting or no starting when cold, white smoke from the stack while cranking, and a rough, lopey idle that smooths out as the engine warms. A failing relay shows the same cold-start complaints because eight good plugs do nothing without power, and a burnt under-valve-cover harness kills plugs and sometimes an injector circuit on one whole bank.

Watch for the tell that separates the two: plugs that get worse cylinder by cylinder point to the plugs or harness, while everything going dead at once points to the relay or controller. Codes narrow it down fast, and the glow plugs keep working for up to 40 seconds after startup, so a rough idle right after firing can still be glow system, not injectors.

How do I test glow plugs and the relay on a 7.3?

Test the plugs at the valve cover connectors without pulling the covers: the glow plug pins are the two outside pins on each connector, and a healthy plug reads roughly 0.5 to 2 ohms to ground. An open circuit or a plug reading way high is dead, and eight plugs tested this way takes ten minutes.

The relay test is just as quick. Key off, you should see 12 volts at the big post closest to the battery; key on with the engine cold, the relay should click and send voltage to the opposite post for the glow cycle. No click or no switched power, and the relay or its control signal is the problem.

What do codes P0670, P0671 through P0678, P0683, and P1396 mean on a 7.3?

These are the glow plug system's fault codes. P0671 through P0678 flag individual glow plug circuits by cylinder, so the code number points at the exact plug or the harness leg feeding it. P0670 is the glow plug control module circuit, and P0683 means the module and the PCM have stopped communicating, which usually means the controller itself.

P1396 on the 7.3 flags the glow plug monitor circuit, often appearing when a bank of plugs reads dead through a burnt harness connection. A cluster of cylinder codes on one side of the engine is the signature of the under-valve-cover harness, and that is when the gasket-harness kit is the right part rather than plugs alone.

Where is the glow plug relay and control module on a 7.3 Powerstroke?

The relay sits on top of the engine near the fuel bowl, a tall solenoid with two large posts that is impossible to miss once you know what you are looking at. The control module lives nearby and talks to the PCM to decide glow timing based on oil temperature, which is why a bad engine oil temperature sensor can mimic glow system failure.

On cold mornings the system should run the plugs at key-on and continue for up to 40 seconds after start. If the wait-to-start light behaves oddly or cycles fast, suspect the module or the oil temperature input before condemning the plugs.

Why do 7.3 valve cover gaskets come with wiring harnesses?

Because on the 7.3 the wiring is the gasket. Ford molded the glow plug and injector harnesses into the valve cover gaskets, routing power under the valve covers through connectors that live in the hottest, oiliest corner of the engine. After a couple hundred thousand miles those internal connections burn and melt.

Replacing the gaskets without the harness would mean reinstalling the burnt wiring, so they ship as one service part. That is also why glow plug work on a 7.3 means valve cover removal, and why doing plugs, harness-gaskets, and the relay in the same job saves pulling those covers twice.

Which glow plug kit fits my truck, OBS or Super Duty?

It breaks at the body change: 1994-1997 OBS trucks take the OBS kits and 1998-2003 Super Dutys take the Super Duty kits, regardless of whether you drive an F-250, F-350, or an E-350 or E-450 van. Within each era, pick the kit matching what you are replacing: harness-gaskets with relay, the same plus controller, or the version with glow plugs included.

A 1996 F-250, a 1999 F-250, and a 2002 F-350 all take 7.3 kits, but not the same one, and the OBS gaskets cross to F4TZ-9D930-K while the Super Duty pieces cross to F4TZ-12A342-BA. When in doubt, send us the VIN and our support team confirms the kit before it ships.

Should I upgrade to a heavy-duty glow plug relay?

Yes, and every kit we sell includes one. The factory relay works but lives hard, switching high current through contacts that pit and stick over years of cold mornings. The heavy-duty relay solenoids in our kits carry contacts sized for the sustained draw of a full glow cycle, which is the same logic behind the popular standalone relay upgrades owners have done for years.

If you are chasing maximum reliability on a plow truck or a rig that starts at dawn in cold climates, the controller-inclusive kits cover the whole decision chain in one purchase. There is no tuning required; these are straight electrical service parts.

How hard is it to replace glow plugs on a 7.3 Powerstroke?

It is a solid driveway job with basic hand tools: remove the valve covers, unplug the external pigtails, swap the plugs, and install the new harness-gaskets with fresh connectors. Budget an afternoon for both banks the first time, and inspect the old connectors while you are in there, because melted pigtails outside the cover need attention too.

Torque the valve covers evenly and in stages, and the truck should fire like new on the next cold morning. If any step gives you trouble, our 24/7 support line walks owners through the job regularly.

Do these kits fit the 7.3 IDI?

No, and it is worth being direct about that. The 7.3 IDI, the indirect-injection engine Ford built from 1988 through mid-1994 with the mechanical injection pump, uses a completely different glow plug system with its own controller and relay arrangement, and the Powerstroke harness-gaskets in this collection do not fit it.

These kits are for the 7.3 Powerstroke, the direct-injection HEUI engine from 1994.5 through 2003. If you are unsure which engine you have, the dead giveaway is the Powerstroke's oil rail and injector design under the valve covers versus the IDI's mechanical pump and hard lines.

Are these glow plug kits street legal, and what is the warranty?

Yes. Glow plug harnesses, gaskets, relays, and controllers are emissions-neutral repair parts with no off-road restriction, unlike the delete upgrades elsewhere in our catalog, which are sold for competition and closed-course off-road use only. Nothing in these kits affects emissions equipment, so they are legal everywhere, inspections included.

Fitment is era-specific between the 1994-1997 OBS and 1998-2003 Super Duty kits, so confirm your body generation or send us the VIN, and our 24/7 support will match it. Every order ships free from our US warehouses, carries a 1-year warranty, and is backed by a 45-day return policy if the fitment is not right.