Which lug are you testing on the relay?

Should be closer to 12v.


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The big lug towards the drivers side. The other big one has 12 volts all the time. I have ready hard starts below 20 unless plugged in. it won't even fire if its below 10. I can't plug in at work so I have had to use ether a couple of times.

 

the output voltage is important, but the voltage drop is what you are looking for. What is the incoming voltage on the "always hot" big post? You should be seeing slightly greater than 12 volts incoming and (this is opinion) 11.8-12.4 volts out when the key is energized and the relay is putting power to the plugs.

 

X2

Are you checking after the key is turned while the glow plugs are activated?


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Reviving an old thread that was never really answered. I also have some cold starting issues with my 1999 7.3. All glow plugs test good. Relay also tests good, but I noticed a 1 volt drop across the relay. With the key on (obviously) the output voltage is 10.8, while the input voltage is 11.8. With the key off input voltage is 12.6. I am wondering if the voltage is too low to really heat up the glow plugs like they should be. I have 130,000 miles on the truck and installed one of the geared high torque starters (which helps a bit). My next step is to run some injector cleaner through the injectors incase they are a bit gummed up. If someone with a truck that starts easily when it is cold can do a quick test, I (and many others I'm certain) would appreciate it. While my original relay seems to be working, I am wondering if maybe the contacts are a bit worn, causing a voltage drop. It is after all almost 20 years old.