93 36v - Possible Dead Short - help please

[cracer250]

I have a 93 ezgo 36v controller cart. It's the metal body cart with no tow switch or anything like that. I've been running the cart with no problems whatsoever for about 2 years. It had new trojans put in a year ago. One day my family came to visit and rode the cart around the block and they had (against my wishes) about 7 people piled up on it. Well, I got a call saying the cart quit and they were stranded. I hauled it home and began to diagnose. I was getting no click on the solenoid so I tested it per instructions on bgw. I couldn't get it to click so I went to the ezgo dealer and purchased a new, heavy duty ezgo 36v solenoid (125.00) figuring that was the problem. I took the old one off, marking all wires so I didn't screw anything up, installed the new one the same way with new diodes on top. Good to go right?????? NO.....I turned the key to ON and it immediately fried the terminal off the big wire post on the ignition switch. Completed melted it off with a bright arc. I bought a new ignition switch and it did the same thing. Fried it off again. So, here's where I'm at. I took all connections off the motor trying to find the short and the motor tested good with an ohm meter. I left the motor wires unhooked and tried the ignition switch again and still got violent arcing at the switch terminal. I can't find any wires that are grounded out or anything like that. I'm thinking that the problem fried the original solenoid and now with a new one, the short is frying the weakest link being the ignition switch terminal. I need some help on where go next with diagnosing my problem. Thanks for any help!!

[cracer250]

I'm dying here!!! Any ideas on my cart? I can hook everything up with no problems until I turn the key switch on....then it burns the switch terminal....

[scottyb]

Do you have a diagram of the cart and digital voltmeter? You will need both.
First check for frame ground. We should never have a ground at the frame. If you do, find it and get rid of that first.
Second this is the basic solenoid activation circuit. See where it is failing in your cart.

[cracer250]

Thanks for diagram. I checked wiring from ignition switch to first micro switch on the F/R. The micro switch was not clicking. It had dirt in it so I cleaned it and that fixed the micro switch. I then checked the second micro switch on the F/R. It works good. Then I traced the wires to the micro switch on the pedal. It also was not clicking. I haven't fixed that one yet, but do you think that would be causing such a short? Oh and there are no grounds to the frame. I have a digital volt meter I've been using.

[scottyb]

So far that's all good news. I don't think you have found your problem yet?
How did you check the motor for shorts?

[JohnnieB]

Unlike ScottyB and many others here, I have no hands on experience with a Marathon, but I can read a schematic and know a bit about troubleshooting.

Since you are burning the terminals off key switches, you most likely do have a dead short, or something close to it, between B+ and B- through the key switch.

Since the key switch is in the low current solenoid activation circuit, the motor and high current cables are not directly involved. They may have been damaged by the cart's weight limit being exceeded, but they wouldn't cause the symptoms described. The controller, except for one possibility (Blue wire from MS-3 to controller pin 1) also falls into same category.

Normally, troubleshooting is done be attaching the negative test lead of your DVM to B- and go looking for B+, but this is one of the situations where you need to do the opposite.
Attach the Positive Test lead to B+ and look for B-

Attach the positive DVM lead to the red wire from battery (B+) to key switch.
Attach the negative DVM lead to the Blue wire going to MS-2 and start with the F-N-R switch in Neutral and the pedal not depressed.
Should read Zero Volts
Put F-N-R switch in F or R.
Should still read Zero Volts.
Press the throttle pedal.
Should read battery pack voltage.

If you get battery pack voltage immediately upon attaching test lead to Blue wire between key switch and MS-2, that wire is somehow connected to B- and shouldn't be.
If you get battery pack voltage when you shift F-N-R switch to F or R, the controller is bad and supplying B- via Blue wire from Pin-1 to MS-3.
If you get Battery pack voltage when pressing pedal, the diode across the solenoid's small terminals is either shorted or installed backwards.

Note-1: Seeing battery pack voltage when throttle is pressed is normal, but if solenoid isn't clicking, the coil is most likely being bypassed by the diode.
Note-2: The current flow that burnt off key switch terminal may have also weld contacts in MS-2 and/or MS-3 closed, so check them to be sure they are working properly.

[cracer250]

Thanks for help. I'll post back my findings....

[simple man]

Just a thought, you stated that you replaced the " diodes ". There should be one diode and one resistor! The diode must be installed in the correct direction, or a short will occur in the activation circuit! Check the diagram very carefully and make sure you have the diode in the proper direction. The resistor doesn't matter as to a direction.

[cracer250]

Wow. I had the diode hooked up backwards. The band was on the controller side of the solenoid. BUT!!! Still shorts out. it will fry badly any connection that is hooked up last with the key on. does not short out when the key is in off position.

Scottyb, I tested the motor with my ohm meter. I have continuity on my common terminals (a1 a2 or s1 s2) but not across any a to s terminals.

[scottyb]

Let us know what all got fried?
I know what fries on the TXT when you do this but not sure what all is smoked on the marathon, seems odd to me your micro switches were intact.