Big electrical short during start up - advice needed.

[XH29N0G]

One of my projects this weekend was to pull the cluster and try to fix the speedometer.  I think I managed to fix the speedometer (and also installed a tach), but when I went to start the car, it would not start.  I noticed the positive cable heating up, but thought that might be due to cranking.  Just now, I had something very strange happen and I think I might have been close to starting a fire.  The engine would not stop cranking, even when I turned off the key it kept cranking.  By the time I ran around and disconnected the batter, the insulation on the positive cable was melting.  I obviously did something when I pulled and replaced the cluster, but I do not know what and am looking for advice on how to proceed.  

I am assuming it is related to the key switch on the steering column.  Should I look somewhere else?  

The things I can tell you are (1) the last time I drove it (before pulling the cluster), I went to the gas station for a fill up and it would not start after the fill up. It cranked over much more slowly than normal.  I ultimately managed to start it and get it home.  After replacing the cluster it also cranked over very slowly.  (2) I may have done something stupid.   In checking the lights for the cluster, I used the steering column - more specifically the key to complete the circuit.  I do not yet know enough about the key mechanisms to know what problems that might cause.  

[garner7555]

It could also be your starter solenoid sticking,  it does make you think it is in the wiring that you did but the starter solenoid could have decided to go out at the same time.

[XH29N0G]

Thank you.  Is there a straightforward way to check if the starter solenoid is sticking?


Would this work?  Since I cannot connect the battery without the starter engaging (even with key off and removed from ignition switch), I am thinking I can test whether it is the starter solenoid or ignition switch by doing the following.

I should be able to disconnect the ignition switch wire from the starter and see continuity between it (through the switch) to the negative batter terminal.  If it is continuous, then the ignition switch is stuck on. If it is not continuous, then it is the starter solenoid that is stuck on.  I cannot think of a test through the starter.  I suppose I could check for continuity between the place where the battery cable connects and the ground (starter body) with the cables disconnected.  That way there would be no way to get 12V at the ignition switch to trip the solenoid.  (maybe a second test?)

Have I missed something?

[Pete in NH]

Hi,

With the positive battery cable disconnected, I would disconnect the other end of the heavy red battery cable from the starter and carefully tape up the ring terminal so it can't short out to surrounding metal. I would also disconnect the brown wire from the starter relay to the starter solenoid. I would then reconnect the positive battery cable to the battery. With the ignition key in the off position you should not have any voltage on the starter relay terminal that you disconnected the brown wire from. If you do there is something wrong it the dash wiring. Try turning the ignition key to the cranking/start position, you should now have voltage on the terminal where the brown wire was connected. If you do have voltage when in the start/cranking position of the ignition key but, not when the key is in the run but not cranking position, the dash wiring is likely okay. If that checks out, use you meter in the ohm meter position and check between the starter battery connection stud and ground. If you see zero ohms the starter solenoid is likely hung up. There is a copper disc connected to the solenoid plunger that gets pushed to connect the battery terminal to the starter motor windings. If the solenoid is hung up it will make that connection and your meter will see the motor windings which are practically a short circuit if the motor is not turning.

Good luck and let us know what you find.

[XH29N0G]

Thanks.  I will do this (probably not today or even before thanksgiving because of other work, but as soon as I can).

If I understand correctly, the heavy red cable powers the starter.  With this disconnected, the starter should not spin.  There is another positive lead to the solenoid that stays on, right?  The voltage the voltage you are describing is between the brown wire and the starter relay. 

[Pete in NH]

Yes, the heaviest red cable from the battery powers the starter. With that cable disconnected at the starter, the starter will not spin. There will still be a red cable from the battery to the starter relay connected. There will still be a brown wire connected at the starter solenoid but, the brown wire will be disconnected at the starter relay. You will be looking for voltage at the starter relay terminal that had the brown wire connected to it. The voltage would be measured with one voltmeter lead on the terminal and the other voltmeter lead on a ground.

[XH29N0G]

So if I understand correctly.  Disconnect the wire labeled 1 in the picture below (tape it well so it does not short).  Disconnect the brown wire at 2B (other picture) but leave attached at 2 (first pic). (I am assuming 2 is the same wire that connects up to 2B on the firewall.)  Measure the voltage (to ground) from post that 2B was connected to.

[Pete in NH]

That's it, you've got it!

[myk]

Wow, excellent advice Pete...

[Dino]

Pete knows electrical!      

[XH29N0G]

Check done. 

Disconnected the wire labeled 1 in the picture below (stuck a piece of tubing over end so it would not short).  Disconnected the brown wire at 2B (other picture) but leave attached at 2 (first pic).  Reconnected battery.  Measured voltage from post of 2B to ground.  0 volts unless key is turned and clutch depressed then just shy of 12 volts.  Also checked continuity between 1 and ground - 1 is continuous with the ground.

I think this means the short is in the starter rather than the switch.  Advice on how to approach it?  I am assuming I need to remove the starter to get at any parts that need work.

Thanks for the advice so far.

[Pete in NH]

Okay, now we know which end of things the problem is on. It sounds like the starter solenoid is hung up for some reason. You can try giving it a rap with a big mallet and see if it will release. But, even if you get it unstuck, there is a good chance it will hang up again. It looks like you're headed for a new starter or at least taking that one apart and see what's going on in there. You can replace the solenoid assembly. The solenoid pushes a fork mechanism that move the Bendix drive forward to engage the engine flywheel teeth. If you have a copy of the factory service manual starter repair is covered in there. If I had the starter out, I  would replace the Bendix drive and four brushes and check out the solenoid as required. Or, the easier thing to do is get a rebuilt starter. Also, make sure the starter is properly mounted on the engine and you don't have a loose mounting bolt or something causing the starter to get at angle that would cause it to jam up.

If I've got a good core unit I lean toward repairing my own as so many of the rebuilt units today are not the best quality.