You would only see voltage on the small studs if the relay is being called for, whether it is or not depends on several factors; time since key turned on (the really times out after a specific time up to about 2 minutes), outside temp, EOT, etc. if the truck doesn't think it needs the GP's it won't call for them to turn on, which means no control voltage for the relay (small studs)

 

I recently learned about how to do a proper voltage drop test in my Master Tech studies. I used a lot of aa1car website information to study for my tests. Voltage Drop Testing I don't have all the specs memorized for different components, but somewhere around .1-.4 volts is all you should see going thru a multimeter when doing certain voltage drop tests. The way it makes sense in my head; if more than about .4v "chooses" to go thru the multimeter, there is excessive resistance in that circuit.

 

If needed for reference, here is a great explanation & video.

https://sites.google.com/site/woodnt...ow-plug-system

 

When my relay started going south I noticed my GPR led not coming on but after 5-10 seconds it would lite up and I could start the truck. When I changed the relay the big posts ended up breaking the housing after loosening them but it physically looked ok. Went with a stancor and have had no issues.

 

Yes it can be intermittent like that. There's a disc inside the relay that completes the circuit and transfers voltage between the two large posts. Thd disc is kind of free floating on a spring, so it can rotate 360°. If one or both of the posts land on a spot on the disc that is corroded, you may not get any or proper voltage pass through to the other large post.

When this starts to happen, making plans to replace the GPR or start carrying a screwdriver you don't mind getting some burn marks on is the best plan.

 

The relay is very cheap. Quit messing around and replace it. When you have an intermittent problem, it is often less stressful to replace a suspect part that is inexpensive. The list of possible causes gets shorter. Also, the relay really is a maintenance item after many miles, much like the glow plugs.

Even if the plugs still work, there are several very good reasons for replacing them. Old plugs can disintegrate and become impossible to remove without removing the head. Also, as plugs start to fail, the engine gradually becomes harder to start and less efficient after starting under cold conditions.

 

I'll explain the "voltage drop" thing:

Reading volts (voltage drop) is showing the difference in volts between one point and another point.

Take a piece of wire that's connected to the battery positive terminal. Don't do this, but if you were to strip some insulation off the wire at about 6 inches away from the terminal - you could read the voltage across the solid wire. This is a closed circuit and it would show no voltage drop - it would show the voltage into the wire at the terminal is the same as the voltage on the wire 6" away (0V).

Now... using the same wire, cut the wire between the terminal and the stripped insulation. That is an open circuit, and you will see a voltage drop that equals the battery volts (12V).

That is essentially a relay's job: Close the wire and open the wire. So... when the relay is off, there should be a voltage drop across the relay equal to the battery volts (12V) because this is a cut wire. Energizing the relay should be like putting the wire back together, and you will see no voltage drop across it (0V). If you see a significant voltage across a closed relay, that would be just like a bad wire - and you would want to replace it.

 

I installed this one in April 2015 and so far so good and it was cheaper than the Stancor at that time.
http://www.ebay.com/itm/Heavy-Duty-Ford-Powerstroke-Glow-Plug-Relay-1995-2003-7-3L-Diesel-/201033503560?hash=item2ece87d348

 

I didn't understand your post. I do agree that the term voltage drop for the test I described is kinda confusing. I would consider it more of a resistance thang, so "the voltage "chooses" to go the path of least resistance" test.

The voltage drop test I described (measuring .1-.5v "drops) across a circuit is great for diagnosing bad connections.

In other Ford related news. 1993 5.0L. Got called in to a no start. The engine bay was totally torn apart from the "last guy" and the "guy before that". Wires everywhere, connectors unplugged, wires with insulation sliced off, dist unbolted, basically a giant mess of misdiagnosis. I found fuel pump relay and the PCM relay had bad connections and this was the core issue! We got spark back at that point! Went to fire it with Ether and got a nice fireball to my forearm while trying to tweak the dist. No hair left on that arm now. Found out ignition wires were crossed. Still backfired. Found out dist was dropped back in wrong. Fixed that and fixed the bad electrical connection= running truck! Owner had a big smile and told me it was then time for him to go get drunk!


Back on topic, 10v OUT of that relay is a red flag. There could easily be excessive resistance inside the relay. Also, I find it hard to believe 8 glow plugs would pull enough current to make it drop to 10ish volts. Simple verification would be to unbolt the OUTPUT of the relay and retest and see what the voltage is. Even so, glowplugs could easily still get warm on 10v. Maybe not warm enough, I couldn't tell ya, but components still work most of the time under 12v. I limped my car to the junkyard the other day with a dead alternator and it BARELY stayed running, but made it, at 8v!

 

This looks like the relay on my snowplow. I have an extra one. So are they probably the same? Or is the diesel one built to withstand more?

 

Probably the same. There was a few posts some years back about people using plow relays as an alternative.

 

My guess is that there are a world of relays out there that will do the job. Electric forklifts and pallet jacks have relays on them as well and they all pretty much work the same. Electricity works a solenoid that passes more electricity (amps). I am surprised that there aren't more moving in on our market, I see a void.