lb7 glow plug wiring

danzick

danzick

playing with fire
Feb 20, 2014
576
16
18
Livingston, MT
I noticed my truck starting like absolute crap when its below about 45. No glow plug codes were tripped, but for some reason, on the drivers side where the wire comes down from the glow plug relay to the first glow plug, it shorted out. like bad. Got so hot it melted the little metal thing that connects all the glow plugs together in half, and melted that first glow plug all up. I started looking for a short, and now im all confused. all of the glow plugs ohm with ground on the stud when they are in the block not connected. Did I short all of them out? or is this normal? I cannot find where a wire has went to ground.
 
danzick

danzick

playing with fire
Feb 20, 2014
576
16
18
Livingston, MT
so what would have caused the connection to burn up like that? poor or loose connection? I would have thought it would burn that 175 fuse in the event of a short.
 
juddski88

juddski88

Freedom Diesel
Jul 1, 2008
4,656
120
63
Chesterfield, Mass.
The fuse can actually handle 175amps of current...the relay, terminals, wires, and bussbar cannot. What gen do you have?? You have the newer controller or the old relay pack?
 
juddski88

juddski88

Freedom Diesel
Jul 1, 2008
4,656
120
63
Chesterfield, Mass.
It's possible you just put in a sticky relay. What I would do is first repair your wiring and clean up any corrosion on terminals etc, then find total ohms of the feeder wire to ground, then calculate theoretical load of the circuit at 12v to verify it isn't supposed to overload the new relay. Then replace the relay with a new one and try again if everything checks out.
 
2004LB7

2004LB7

Well-known member
Dec 15, 2010
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juddski88 said:
It's possible you just put in a sticky relay. What I would do is first repair your wiring and clean up any corrosion on terminals etc, then find total ohms of the feeder wire to ground, then calculate theoretical load of the circuit at 12v to verify it isn't supposed to overload the new relay. Then replace the relay with a new one and try again if everything checks out.
Click to expand...
this could be quite difficult to measure without a calibrated wheatstone bridge or other meter built for sub one ohm measurements. each glow plug is about 1/2 ohm. multiply that x 4 and you end up with 1/8th ohm. most meters have a hard time measuring less then 1 ohm. the difference between 1 ohm and 1/8 ohm is 10 amps and 100 amps.

it would be easier to just put all new glow plugs in and measure the current with a DC clamp meter or calibrated shunt.

more then likely the melting was due to high resistance in a connection or corrosion in the wiring that increased the resistance and thus heat generation. a sticking relay will more then likely just burn out the glow plugs before melting the wiring / buss bar if they are in good shape
 
danzick

danzick

playing with fire
Feb 20, 2014
576
16
18
Livingston, MT
2004LB7 said:
this could be quite difficult to measure without a calibrated wheatstone bridge or other meter built for sub one ohm measurements. each glow plug is about 1/2 ohm. multiply that x 4 and you end up with 1/8th ohm. most meters have a hard time measuring less then 1 ohm. the difference between 1 ohm and 1/8 ohm is 10 amps and 100 amps.

it would be easier to just put all new glow plugs in and measure the current with a DC clamp meter or calibrated shunt.

more then likely the melting was due to high resistance in a connection or corrosion in the wiring that increased the resistance and thus heat generation. a sticking relay will more then likely just burn out the glow plugs before melting the wiring / buss bar if they are in good shape
Click to expand...
This is kinda what I was thinking. It's like a poor connection with an extension cord. I was just confused when i put my meter on the power lug from the relay and the battery ground and there was a connection.
 
juddski88

juddski88

Freedom Diesel
Jul 1, 2008
4,656
120
63
Chesterfield, Mass.
2004LB7 said:
this could be quite difficult to measure without a calibrated wheatstone bridge or other meter built for sub one ohm measurements. each glow plug is about 1/2 ohm. multiply that x 4 and you end up with 1/8th ohm. most meters have a hard time measuring less then 1 ohm. the difference between 1 ohm and 1/8 ohm is 10 amps and 100 amps.

it would be easier to just put all new glow plugs in and measure the current with a DC clamp meter or calibrated shunt.

more then likely the melting was due to high resistance in a connection or corrosion in the wiring that increased the resistance and thus heat generation. a sticking relay will more then likely just burn out the glow plugs before melting the wiring / buss bar if they are in good shape
Click to expand...
The Equivalent Resistance of the 8 glows at .5 ohm each is .063, which yes, is too small to measure with an average tool. That's why I suggested to ohm the feeders where they connect to the relay block, so he measures the whole system, which should be much more. Otherwise the system would be pulling greater than 175 amps. The total resistance should be somewhere closer to .25 Ohms to pull 50 amps on the Relay which IIRC is rated at 60Amps.
 
2004LB7

2004LB7

Well-known member
Dec 15, 2010
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danzick said:
This is kinda what I was thinking. It's like a poor connection with an extension cord. I was just confused when i put my meter on the power lug from the relay and the battery ground and there was a connection.
Click to expand...
depending on what you measured you may have been measuring the resistance of the glow plugs by doing that. relay goes down to the glow plugs and glow plugs go to ground
 
2004LB7

2004LB7

Well-known member
Dec 15, 2010
6,987
2,146
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Norcal
juddski88 said:
The Equivalent Resistance of the 8 glows at .5 ohm each is .063, which yes, is too small to measure with an average tool. That's why I suggested to ohm the feeders where they connect to the relay block, so he measures the whole system, which should be much more. Otherwise the system would be pulling greater than 175 amps. The total resistance should be somewhere closer to .25 Ohms to pull 50 amps on the Relay which IIRC is rated at 60Amps.
Click to expand...
I'm pretty sure there rated for much higher than that. I think there is two 100 amp relays inside the controller. the glow plugs could draw 100 amps or more depending on voltage. a 60 amp relay wouldn't last very long at those currents
 
danzick

danzick

playing with fire
Feb 20, 2014
576
16
18
Livingston, MT
I think when I tried to slide the bar into the glow plug stud with the nut on, I missed and the slotted hole for the bar was actually making a connection by the base. You can see the stud didn't get any damage.
 

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