Glow plug relay question

[DokWatson]

Before anyone jumps down my throat to search, I have. Thats how I got this far. I used the attached picture as my guide.

The relay functions as it should. It clicks on and off when I press my glow plug button. I have 12 volts at the top, and 12 volts to the two smaller posts with the key in the run position. However, I don't have 12 volts coming out the bottom. I have 4 1/2 volts with the relay energized, I'm lost as to what the problem is and help would be appreciated.

 

[nattieleather]

Is the relay gounded properly. If it doesn't have a good gound side to complete the 12V circut that could be a problem. Also if the relay is bad it could be shortin out internally. Try taking the 12V off the tops and test if the circut is closing properly. A VOM set to short on either terminal. Hit your switch to close the relay and see if your getting good connectivity.

 

[DokWatson]

Checked that already. Still don't see where the problem is.

 

[DokWatson]

I disconnected all the glow plugs, and what do you know...12 volts on the bottom post. This is really weird, I tested all the plugs and they checked out. Maybe I didn't test the plugs right.

 

[antennaclimber]

What is the voltage at the top post of the relay when the relay is closed (energized) and the GP's are connected?

If it remains at 12 volts and the GP side drops, then the relay may be bad.

If it drops to the same voltage as the GP side, then your problem is before the relay.
Karl

 

[mistaken1]

In a stock system that top post should have 24V on it.

If you have converted to a 12V glow plug feed then that top post will have 12V.

Sounds like your relay is bad.

The coil is energized all the time the key is on. When you ground the small terminal with the blue wire current flows through the coil turning it into an electromagnet. This in turn causes a contact block to move so that the large power terminals will conduct electricity. If the internal contact points on the power terminals are bad you will not get full voltage through there when under a load (glow plugs connected). When you test without the glow plugs (no load) the voltage is normal.

Basically the bad contacts cause resistance in the circuit, the more current that flows the greater the voltage drop through that resistance (bad contacts). The glow plugs draw a lot of current, the test meter draws very little.

 

[DokWatson]

Its a 12 volt system. Relay is fine, its brand new. The glow plugs were bad, I think I tested them wrong the first time. Put new ones in and the voltage will slowly climb towards 12 volts with the relay engaged.

 

[DokWatson]

I just realized what was wrong! Whoever did the 12 volt conversion didn't bypass the resistor bank! I was getting the normal voltage drop+the resistor necking down the voltage, No wonder I only had 4-5 volts. D'oh!