Fried resistor

[3panther]

This happened with my first CUCV. Today, the resistor bank fried itself, and now, of course, I have no response to a turn of the key- nothing- dead. My buddy has an extra one on a parts truck but it's a few hundred miles away. I was considering bypassing the resistor bank just to get it started, but might this fry the relay? Once it's running, there is no current passing through, so I wondered how long I would get away with this bypass? Also, what causes the resistor to burn up like that in the first place? Thanks in advance for any help.

 

[doghead]

If you have absolutely nothing, you have another issue besides the resistor. It is only used to supply the glow plugs.

You can easily disconnect the resistor and resupply the GP relay with 12 volts directly off the 12v stud just above and to the left of the GP relay. This eliminates cascading GP failures and eliminates the resistor.


As for having nothing, you probably blew a 12 volt circuit fusible link(supplying the 12 volt stud described above).

 

[Ken_86gt]

I doubt that you fried the resistor, more likely a fusible link. I would not replace it if it is fried- by-pass it to the 12v bus. Search for this if you need more info or help.

 

[3panther]

Thanks Doghead- what size gauge is that link?

 

[doghead]

Off the top of my head, I don't recall the size. It should be labeled. If not, check in tomorrow and we'll find it in the TM, or Warthog may jump in with more information.

 

[paraclete comes]

good info I may just try to wire the old glow plugs up to 12 volts as a matter of precaution.

 

[doghead]

good info I may just try to wire the old glow plugs up to 12 volts as a matter of precaution.

I usually recommend this.

 

[3panther]

So once I disconnect both resistor ends, the relay end will be wired directly to the 12V bus on the firewall, and the other side (battery side) is connected where?

 

[Speddmon]

Search "resistor bypass" in the CUCV forum using advanced search...lots of instructions there.

Basically, you only disconnect the wire at the top of the relay that came in from the resistor...tape that wire up really good. Then, place a wire from the 12 volts bus (Diamond shaped block above the relay) to the terminal where you removed the wire. Thats it

 

[3panther]

So if a fusible link is blown, wouldn't it be visibly melted or burnt? None of the fusible links in the circuit LOOK fried. I'm gonna clean everything up, put it all back together, make sure it's all tight and see what happens - and I'm hoping when I turn the key I get lights/voltmeter- something

 

[cpf240]

Not always... they can burn without it being visible from the outside.

 

[3panther]

If you have absolutely nothing, you have another issue besides the resistor. It is only used to supply the glow plugs.

You can easily disconnect the resistor and resupply the GP relay with 12 volts directly off the 12v stud just above and to the left of the GP relay. This eliminates cascading GP failures and eliminates the resistor.


As for having nothing, you probably blew a 12 volt circuit fusible link(supplying the 12 volt stud described above).

So Doghead what causes the fusible link to fail in the first place? A short somewhere along the wiring harness? Bad / insufficient ground? Both of these and more?

 

[doghead]

Age, corrosion, overloads, shorts, vibration, and probably a few other things.

Never test continuity with your eyes, use a digital multimeter. ("it looks good")

 

[4x4 Forever]

All of the fusbile links that have blown on me showed no outside signs of it being blown. As DH recommended, check with a multimeter.

Good Luck!

 

[3panther]

Attach to the larger of the 2 posts on the 12V bus?

 

[doghead]

Yes, although they are both connected.

I prefer to use the bigger one.

 

[3panther]

OK- I bypassed the resistor bank; replaced a fusible link attached to the 10gauge wire from the rear battery's negative terminal; checked ignition fuse on panel under dash and it was good; now, at pre-ignition key turn, Gen 2 light and a weak wait light are lit, but no starter crank, no voltmeter, no Gen 1- what am I missing? Left side of resistor bank is still connected to the positive terminal board- should that be disconnected? I'm going to test for voltage with my multimeter along the circuit - it doesn't help that the truck broke down remotely from where I am now

 

[3panther]

If I disconnect the resistor's connection to the GP relay, should I also disconnect the connection to the positive terminal board?

 

[3panther]

I've got a multimeter but am a rookie in its use- testing for continuity, I touch the black probe to part of the body for a negative ground, and touch the red probe to the connection, and continuity is displayed in voltage? What voltage am I looking for?

 

[MarcusOReallyus]

No, continuity isn't measured in voltage. You are checking to see if the conductor is intact. You need to DISCONNECT THE CONDUCTOR BEING TESTED FROM THE BATTERY in order to do a continuity check. You'll use the OHMS setting. Ohms are a measure of resistance. Too much resistance is bad.

The value you are looking for depends on the circuit being checked. I don't have the actual numbers for the CUCV, but if it's a power lead, generally you shouldn't see more than a few ohms for such a short distance. Really, it should be pretty close to zero.

If you are measuring volts, you can get an indication of there being SOME continuity, but you could still have significant resistance in the line and not know it. Here's an example:


BATTERY --------------- CORRODED CONNECTOR------------------ TEST POINT


If your wire is not connected to any kind of load after the TEST POINT, you'll measure full battery voltage there even with that corroded connector in the line, and you won't know you have a problem. "Hey, I got 12 jolts, so I'm good!" You think it's good, but it's not.



Now put a load on that same circuit, and it might look something like this:

BATTERY --------------- CORRODED CONNECTOR------------------ TEST POINT --------- LOAD --------- GROUND

Now in this situation, you will measure something less than battery voltage at the test point. How much? That will depend on the resistance of the load and the resistance of that corroded connection. If they happened to be EQUAL resistance, you'll measure exactly half of battery voltage at the test point. That ain't likely, but it illustrates the point.

You can see what that would do to your glow plugs. They are the load when you try to use them. You measured 12 volts at the GP connector, you think they are getting 12 volts, but they aren't. And you are left scratching your head.


Now back to the first diagram:

BATTERY --------------- CORRODED CONNECTOR------------------ TEST POINT

If you measure this using the ohm scale, you'll see exactly how much resistance you have, and you'll see you have a problem. It OUGHT to be close to zero, but it's not. So, you go looking for that source of resistance. You find it, you clean it up, you double check and life is good.


Measuring using the ohms scale can be messed up if there is voltage present. So, either disconnect at both ends, or disconnect the battery.

Does that help?