Where is fusible link for glow plug timer - 1992 Ford F250

Hi Margaret , Does the glow plug wait to start indicator light on the dash come on ? And then go off after a couple of min. ? Check fuse K 20 amp in the under hood fuse box .This is one of three B+ power supplies to the glow plug control module > Two fusible link's are also B+ power supplies to the module . There is a 10 amp fuse located in the inside fuse box , fuse # 17 , this is power for the indicator light !

Follow the glow plug wires to a common box where all the glow plug wires congregate. This should be the timer.

Offhand I would say that the Ignition Relay or Ignition switch is bad. You will not be able to start a cold diesel without the Glowplugs. If you think about what works and what does not work when the ignition key is not turned on, many of the things match your problems.

If you lost your Ignition the truck would stall and just quit. Usually the headlights would still work. The Wipers would not work without the Ignition being in the ON position. Not sure how your horn is wired but most Honk with the Ignition in any position.

Now there is a difference when you say it won't start: whether you mean it does not crank or that it cranks but will not start. If the Ignition is working-the Glow plug Timer should cycle, but it will need power from the power Relay. So when you turn the key you should hear the timer.

There can be a Master power fusible link. It should be near the battery. You can go register your truck at Autozone.com and get free wiring diagrams.

Please comment on my info.

try fuseable link at battery possitive. check all fuses

Check for power on the glow plugs. You have two fusible links on the passenger side by the stater relay and a plug going over to the engine. These plugs get intermittent and that can cause your hard starting; the glow plugs themselves maybe burnt off. I've seen this happen with the other Ford diesels in our tow trucks!

P1391 Glow Plug Circuit Low Input (Bank #1)

• DTC P1391 or P1393 will set when the monitor indicates that all four glow plugs are not being powered on that bank. An open in the glow plug circuits, glow plug relay, glow plugs or monitoring circuit could be the possible causes.
  
  Both DTCs P1391 and P1393 together will set when the monitor indicates that all eight glow plugs are not being powered. An open in all glow plug circuits, the glow plug relay, glow plugs, fusible links or all three monitoring circuits could be the possible causes.
• Possible causes:
  • glow plug relay
  • glow plug shunt
  • open in glow plug circuit(s) or monitoring circuit(s)
  • glow plugs
  • PCM

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HI. This is an indication of a failing glow plug. It will be necessary to test each plug to isolate the issue, or run a diagnostic scan on the CPU. During the scan, you should be issued a code that will isolate the actual glow plug that is malfunctioning. If you insist on testing each plug, use my procedure below to assist. You can find the resistance specs in your operators manual.


A test light can be used to determine if the glow plugs are working.


1. With the test-light grounded, insert the test light probe into a glow-plug wire to check for continuity.

2. If the light comes on, check the other cylinders in the same manner. If the test light failed to light, check for continuity at the glow-plug relay.

3. If no power is present, check the control circuit of the glow plug relay.

4. If the control circuit is working, the relay may be defective (FYI, manufacturers may have the system fused and fusible links may be located throughout the system).

5. If the glow-plug circuit is working, the glow plugs themselves may be defective.

Checking glow-plug resistance:(Remove the plug for this test)

1. With an ohmmeter, connect one lead to the terminal and the other lead to the body.

2. Read the resistance and compare to specifications.

3. A visual inspection may also be necessary to check for excessive carbon buildup and physical damage to the tip.

4. A glow plug that has excessive carbon deposits on its tip can give the correct ohmmeter reading but still not work. Clean the tip with carbon cleaner.(DO NOT USE A BRUSH TIP CLEANER)

HI. Usually, when this light illuminates, it will signal that one, or more of the glow plugs are malfunctioning. I recommend to test all glow plugs, so that you may isolate the defective plug.

A test light can be used to determine if the glow plugs are working.


1. With the test-light grounded, insert the test light probe into a glow-plug wire to check for continuity.

2. If the light comes on, check the other cylinders in the same manner. If the test light failed to light, check for continuity at the glow-plug relay.

3. If no power is present, check the control circuit of the glow plug relay.

4. If the control circuit is working, the relay may be defective (FYI, manufacturers may have the system fused and fusible links may be located throughout the system).

5. If the glow-plug circuit is working, the glow plugs themselves may be defective.

Checking glow-plug resistance:(Remove the plug for this test)

1. With an ohmmeter, connect one lead to the terminal and the other lead to the body.

2. Read the resistance and compare to specifications.

3. A visual inspection may also be necessary to check for excessive carbon buildup and physical damage to the tip.

4. A glow plug that has excessive carbon deposits on its tip can give the correct ohmmeter reading but still not work. Clean the tip with carbon cleaner.(DO NOT USE A BRUSH TIP CLEANER)

I think the timer is under the sloinoid wich is under the airfilter. My timer went out so i just ran some wires from the sloinoid to a toggle switch in my truck and just warm em up like that, i just took the timer out of the equation

check the temp sensor or low resistance in the glow plugs first