Electrical woes...

[StoneMill]

Getting the deuce back together and ran into some trouble with the wiring. I bought a new harness from od iron. Everything matches up except where the wiring comes through the firewall there are two wires (74a and 74b) that were not on the original harness. We left them unhooked. Everything else hooked up just like the previous harness. Went to hook up the batteries got a nasty surprise when the cable arced. We've retraced most of the wiring. All looks good. Starter is connected as it was. Lost right now. Any help???

 

[Speddmon]

According to the schematic, 74a is for the start button. 74 is the hot side of the start button, comes out of the start button as 74a. 74a goes to the fuel pressure switch and then comes out of the fuel pressure switch as 74B and goes to the start relay.

 

[StoneMill]

Where does it connect to the fuel pressure switch? I see no place to connect it. The original harness didn't have it.

 

[StoneMill]

I'm reading posts and looking at schematics. From what I read, only the tractors have the fuel pressure switch. Is that the case, and if so, what'd I need to do with these wires. Tie them together? Wish I had this thing started already.

 

[Speddmon]

If you have no fuel pressure switch, then yes, you'll need to hook them together because the other side of 74B should be going to your start relay.

Essentially then you'll have 74A coming off of your start button and going straight to 74B (the two you tied together) and 74B to your start relay.

But not knowing what was causing the large arc you got from the battery I can't help you out much there because these two wires shouldn't have done that.

 

[StoneMill]

Okay, I'm going to wire the fuel pressure switch wires together. Then I'm going to go through all the wire harness again and see what caused the arc. Any suggestions besides going through and checking each wire. thanks....

 

[glcaines]

I think you are going to need to go through each wire. I would disconnect a lot of the wiring harness and check with an ohmmeter. There is a short to ground somewhere if you are getting a large arc. Check with an ohmmeter to avoid damage to something. Once you get to the situation where the short is removed, start reconnecting until you find the cause.

 

[StoneMill]

Don't really know what I'm doing with an ohmmeter. How should I go about checking the harness with it?

 

[glcaines]

With an ohmmeter, you can measure the resistance of the circuit. After you disconnect circuits from the wiring harness, place one lead of the ohmmeter on ground and the other lead on the positive batter lead. Make sure the positive battery cable is disconnected from the battery before starting. With everything turned off and/or disconnected, you should not get a reading. It is more convenient if you have a meter that sounds a beep. if you have a short circuit to ground somewhere, the meter will tell you, and you don't risk damage to anything. When the meter indicates an open circuit, simply keep adding connections until you see the resistance go to near zero, or the meter beeps. This will identify where the problem lies.

You can test the meter ahead of time by shorting out the test leads. If you don't have an ohmmeter, you can pick up a very inexpensive one from Radio Shack, or other sources. This is a very useful instrument to have and they are very easy to use.

 

[Warthog]

So you own a ohm meter and don't know how to use it?

Here is a Deuce wiring diagram.

 

[G-Force]

An easier way to do it would be to remove the 24 volt + cable from the battery and put a 24 volt test light in between the battery post and the cable end (If you don't have a 24 volt test light put two twelve volt test lights in series. Otherwise a 12 volt test light bulb won't last that long). When you connect the test light and there is any short to ground the light will light up. Go and start removing your connections until the light goes out. When the light goes out that wire is your shorted one. I would start at the alternator wire. It could be a bad rectifier in the alternator.

 

[StoneMill]

So you own a ohm meter and don't know how to use it?

Here is a Deuce wiring diagram.

Yup, thanks for pointing that out. I know how to use it with in home wiring just haven't used it much with automotive and want to make sure I'm diagnosing this right. Thanks for the diagrams. Went through them yesterday and things check out so far. I must be missing things somewhere.

Glcaines, thanks for your post. I'll see what I can figure out today.

 

[StoneMill]

An easier way to do it would be to remove the 24 volt + cable from the battery and put a 24 volt test light in between the battery post and the cable end (If you don't have a 24 volt test light put two twelve volt test lights in series. Otherwise a 12 volt test light bulb won't last that long). When you connect the test light and there is any short to ground the light will light up. Go and start removing your connections until the light goes out. When the light goes out that wire is your shorted one. I would start at the alternator wire. It could be a bad rectifier in the alternator.

With the arc we had yesterday, the batteries have been disconnected. Can I hook up all but the positive cable, then connect the test light from positive to battery without an arc.

 

[StoneMill]

I hooked my ohmmeter to the pos and
neg cables. Reading was like 104.2. Disconnected the alternator wire and the meter goes back to 1 like when it is not connected. Guess that means the alternator is the issue?

 

[StoneMill]

Before we started tearing things down the truck functioned fine. No electrical problems to speak of. Do rectifiers just go out for no reason? Just thinking there has to be more to it than just the alternator.

 

[StoneMill]

Used the ohmmeter again between the positive cable and positive terminal of the batt. Read 25 volts. Disconnected the alternator and it reads 4 volts. Hooked up the batts with alternator disconnected and no fireworks display. So, this leads me to believe that the alternator is the issue. Do alternators just die like that. Has been disconnected for a couple months, lying on a shelf. Worked fine prior to disconnecting. Anything else I should check or should I just drop $190 on a new alternator listed in the classifieds??

 

[nk14zp]

Is it hooked up right?

 

[area52]

The alternator uses a charge from the battery to "flash" the field, it should have a diode to prevent the current from flowing from the alternator into the battery. Maybe you are missing that diode?

 

[StoneMill]

I believe the alternator is hooked up right. Matches the diagram. #2 wire goes from main positive lug on starter (where battery + attaches) and feeds under two screw clamp to lug on alternator under plastic cap. Smaller wire is attached directly next to it and is covered with black silicone, then plugs into wire harness. Alternator has a good ground to bolt holding fuel filter bracket.
I wouldn't be surprised to have messed something up, but so far everything looks like it's in the right place. Since disconnecting the alternator drops the voltage back down and I can then hook up the batteries without sparks, I assume that the alternator is the culprit.
Is it okay that the meter still shows 4 volts when the alt is disconnected? What else could cause this and/or what should I look at. Sorry, I'm new at this.

 

[Barrman]

Is your on/off switch on? It could be on and exciting the alternator. As pointed out above, power goes from the batteries through the big line to the alternator and the # 11 wire to the breaker on the firewall. Might want to unplug 11 at the breaker and then see what happens with the alternator.

Another option is the exciter wire for the alternator. That little metal cover can sometimes short out the exciter wire or/and the big wire at the alternator. Since it worked before, I am thinking it is something kinked or shorted. As pointed out above.