Put control light on GP relay and see how it works

 

Either a glow plug (or more) has already failed, or one (or more) has a problem in the wiring, or the relay is bad.

I like to test each wire/plug from the connector at the relay. First, test for a dead short with your multi-meter on each point on the connector.

After that, test for current draw. I have an old-school ammeter gauge, meant for dash mount, the can measure up to 50 amps. I attached heavy copper house wire to the gauge. Put one wire in hole in the connector, put the other wire to a 12v source, and watch the gauge. Each plug should start out pulling about 15 amps which drops off to 8 amps or less as the plug heats up.

If no current draw, you have an open circuit. If all the plugs / wires are good, then your relay is probably bad. Note there are other inputs to the relay, you could have a fault in one of those wires / circuits, but not likely.

 

Either a glow plug (or more) has already failed, or one (or more) has a problem in the wiring, or the relay is bad.

Im thinking the relay is bad. always giving power to the glow plugs.
Temporary fix. I tapped into the ground wire and connect a temporary push button switch to turn the relay on and off.
works good for the first start of the day.

 

Beware that few extra seconds with manual switch can burn all the GP.
Did you check ebay for used relay? They should be cheap .

 

The GP are only on as long as i have my finger on the temporary switch. Just a few seconds to warm them up.