Quote:
Originally Posted by Mxfrank
Not exactly. The current flowing through the #1 plug is compared to the total current flowing through 2-5. If the ratio isn't 1:4, then the indicator light is turned off during the preglow cycle, but will come on later.
The result is very wonky, because the way that current is measured is with two coils on either side of a magnetic switch. One coil has 4 times the number of windings on the other, and is counterwound. These coils supply power to the plugs. When ratio of the currents is exactly 1:4, the magnetic fields created by current flowing through the coils are equal and opposite, and the magnetic switch isn't activated. So odd situations can occur when more than one plug is bad, or when the resistances aren't all in spec. My policy is to replace all the plugs whenever the lights go nuts.
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Mr. MxFrank has it right. It is a current balance relay. There are cases where you can lose more than one plug but the relay will not catch it.
Best thing to do here is go ahead and do a full plug replacement since you don't know the history. Time to bite the bullet and pull the manifold. Yes someone will chime in and say you don't need to do that, but on a 60x you pretty much have to, unless you like having to contort yourself to get around all the obstructions. And unless you happen to have the perfect length tools to get in there, and be able to rotate them through a useful fraction of the circle, without hitting anything down there.
You can of course try the simple ohm test from the connector. But the only thing I trust in that regard is if I get a high reading then it has definitely failed. Low resistance won't tell you anything. The element could be shorted halfway along the length, which would pass the ohms test, but won't get hot where it counts, at the tip.
You can pull them and do the jumper cable and vice trick, but you've already got them out by that point, so I would go ahead and put in new ones on principle. Unless you just wanted to confirm that glow plugs was the problem, and not something more serious like low compression, the vice trick is a waste of time in my book.