how to test if glow plug relay is working?

[GREASE FIRE]

my truck came with a manual glow plug set up that was hastily rigged up by the previous owner but i never got to asking him if the stock relay actually failed or if he rigged it up for another reason.
from what i have read, the manual system is risky because it can burn out multiple plugs at once so i am thinking of going back to the stock set up, especially because i have an extra relay i could use if i find the one on the truck does not work. All i know for now is that when i turn the key on the "wait to start light" comes on for a while, depending on how cold it is outside, then goes out. It stays on anywhere from a few seconds to up to around 15 secs on a very cold day, so obviously the timer aspect of the relay works.

although i have tested each individual plug with a simple 12 volt tester for continuity and they all seem "good" i have concluded that my glow plug system is not actually working. A local mechanic is going to help me with this one to figure out where the problem is, and i think while i am at it i will restore the automatic glow plug system.
So, i first need to figure out how to test to see if the stock relay is good or not. Anyone know how to do this?

i might actually keep the manual push button set up there, but run the heavy wire from the extra solenoid that was used for it to the heavy terminal on the stock relay, that way everything would work as normal but i would just have to press in the button to ensure the gp's get power. that way, if the relay fails in the "on" position it won't burn them all out because as soon as i let go of the button it will cut power. Can anyone comment as to whether that would be a good idea or not?

thanks,
Paul

 

[Agnem]

It would help us if you created a signiture for yourself telling us about your truck. Of particular interest at this point, is the YEAR.

 

[subway]

well i just pulled all mine out yesterday and manually tested them with a battery charger to see if they got red hot. they all did within 7-8 seconds except one. i was not haveing any luck gettign any reall readings with my ohm meter so i did it the hard way.

just wanted to take a minute to curse the ones under the turbo, of course that is where i had a dead one.

if you do rig up a push button that is the way to go, a SPST switch that is normally off. that way they will only come on if you are actally pushing on it. i dont really see a problem with this set up as long as you or the person driving knows what they are doing. if someone comes in and fires them puppies for 30 seconds or more you could be in for some work with swelled tips.

 

[1dieselman]

Just wanted to pipe up about the easiest way I have found for testing glow plugs without pulling them. I use a 12 volt test light. Clip the wire end to a positive battery post, and probe the glow plug with the harness connector pulled. If light comes on plug is good if it doesn't time to change it. Always works for me.

 

[GREASE FIRE]

Just wanted to pipe up about the easiest way I have found for testing glow plugs without pulling them. I use a 12 volt test light. Clip the wire end to a positive battery post, and probe the glow plug with the harness connector pulled. If light comes on plug is good if it doesn't time to change it. Always works for me.

that has always worked for my 6.2 glow plugs as well - and according to that same test all the ones on my 7.3 are good. But for some reason they are not working...

 

[GREASE FIRE]

It would help us if you created a signiture for yourself telling us about your truck. Of particular interest at this point, is the YEAR.

sorry i forgot about that. its an 89 f250 7.3

thanks,
paul

 

[Agnem]

OK, so you have the 7.3 system, which we all generally regard as being very reliable as long as everything is well connected. What usually seems to happen with that system, is the controller will short cycle because of bad plugs, a bad electrical connection, or a bad ground, and somebody will just try to hotwire it instead of fix it because they don't understand how it works. An easy way to see if the contactor is working properly, is to connect a test light across the large terminals. It should glow brightly when the "wait to start" light is NOT lit, but go out COMPLETELY when the wait to start light IS lit. If the test light glows AT ALL during glow time, then there is excessive resistance in the contactor.

 

[GREASE FIRE]

thanks for the explanation - and it sounds like a very good description of how the previous owner did things, like he just hotwired it because he didn't fully understand how it worked. I will do the test as you describe and hopefully that will help me figure it out.
now, there is just one other major quirk about the system, something i recently discovered and i just want to see if anyone has some ideas about it.

basically, when it is cold it almost never starts on the first crank, even a long one (and as i said in previous posts, brand new batteries, starter, alternator and turns over extremely fast). BUT, on the second crank, it usually starts pretty easily. It almost seems like the glow plugs don't operate on the first crank for some reason, but then after a good long crank when i cycle them again then they work. Is that even possible?
All i know is that it was very cold here yesterday and, without the block heater i did this: glow plugs about 10 seconds, then 5 - 10 seconds of cranking and nothing at all; then wait a minute, another 10 seconds of gp's then just a few seconds of cranking and it fires right up.

anyone else have this scenario?

thanks,
Paul

 

[sle2115]

If it is very cold, 10 seconds is too short. Mine probably stay on for 20 to 30 seconds on a really cold day. You could also have someone press the button while you put a test light in each glow plug connector (all unhooked to avoid prolonged burn time). They also have an issue with the controller ground. At any rate, maybe try adding five seconds, then try to start, I'll bet it hits off. If you want to be really safe, try adding one second, then next time its cold, add two, then next time its cold, add three, etc. The first few times mine cycled, I was scared to death because everyone said 10 seconds, it was cold and I know they were on at least 20, I was sweating bullets. Now, two years later, other than a fried fusible link that it about to be permanently fixed, they are still running the same and I'm still running the same set of Motorcraft (BERU) glow plugs.

 

[subway]

An easy way to see if the contactor is working properly, is to connect a test light across the large terminals. It should glow brightly when the "wait to start" light is NOT lit, but go out COMPLETELY when the wait to start light IS lit. If the test light glows AT ALL during glow time, then there is excessive resistance in the contactor.

might have to try that, i still feel like mine are short cycling and i cleaned all the connections on the relay.