1988 Marathon Rewire Short

[jcloven]

Hi all. First post. Be gentle

I just got a 1988 Marathon. When I acquired it, it had no key switch and had been hotwired. It was a mess.

I installed all new electrics between the motor and the foot pedal.
Contact board
Solenoid
Sweeper
Complete FNR (with MS1 and MS2)
Key Switch
2ga cables
Coil pack

The only parts I'm reusing are
MS3 (stop/go on contact board) (Forgot to order one, but it tests good. No resistance when closed. No contact when open)
2 motor cables
Charger port.

The charger port is not connected, but is shown in my (amateur) schematic.
There was a 36-12vdc voltage reducer, but that is not installed and is NOT on my schematic.

With the KEY OFF, FNR REVERSE, the cart does NOT move and, apparently, there is a dead short.
Sparks when I move the FNR and the battery terminals are getting crazy hot.

With the key on and the FNR in forward, the cart DOES move.

I have NOT tested KEY ON, FNR FORWARD to see if the terminals get hot as I don't want to risk damage.

I have attached photos of my set up and a really terrible schematic of how it's wired. The grounds are disconnected for obvious reasons. Any assistance that anyone can provide will be greatly appreciated. If anything is unclear, by all means, please ask

Thank you in advance.

 

[Golf Cart Wizard]

It appears you have a dead short in the schematic. I'd look for a wire diagram on this site to follow, this might work: EZGO Marathon Golf Cart Wiring Diagram Resistor Coils

 

[jcloven]

It appears you have a dead short in the schematic. I'd look for a wire diagram on this site to follow, this might work: EZGO Marathon Golf Cart Wiring Diagram Resistor Coils

Thank you for that. I've seen that one before, but I'm not seeing MS1 anywhere. Am I just missing it?

 

[jcloven]

UPDATE: Multimeter test results are below.

Disconnected B- to S2 for testing.
Disconnected all cables to post side of contact board (CB)
Connected sweeper contact to SOLENOID OUT.

I switched the posts I was using on the key switch. I bought a three position switch and I belive I was on the accessory side. Probably shouldn't make a difference, but it's correct now.

Grounding to B- for all tests.

THE MICROSWITCH (MS) TRAIN

KEY OFF - FNR FWD
No voltage at any point in the MS circuit.
SOLENOID LOW OUT 0v
SOLENOID HIGH OUT 0v
FNR6/B+ (clock position) 36v
FNR9 36v
FNR12 0v
FNR3 0v

KEY OFF - FNR REV
No voltage at any point in the MS circuit.
SOLENOID LOW OUT 0v
SOLENOID HIGH OUT 0v
FNR6/B+ 36v
FNR9 36v
FNR12 31v
FNR3 31v

KEY ON - FNR FWD - PEDAL UP -
Good voltage at all points on the MS circuit through SOLENOID LOW IN
SOLENOID LOW OUT 0v
SOLENOID HIGH OUT 0v

KEY ON - FNR REV - PEDAL UP - Same as above.

KEY ON - FNR FWD - PEDAL DOWN -
Good voltage across the MS circuit.
Solenoid clicks.
Good voltage from Solenoid Low Amp Out.
Good voltage from Solenoid High Amp Out.
Good voltage at SWWEPER CONTACT/CB1.

KEY ON - FNR REV - PEDAL DOWN -
Same as above, plus back up warning works.

So I belive I'm good through the entire switching process. Please correct me if I'm wrong or missing something.

Including a picture of the front of the FNR. I have MS2+ piggybacked from MS1+... at least I think I do. If that is wrong, please let me know!

HIGH AMP CONNECTIONS

FNR WIRING (Clock positions)
3 TO S1
6 TO B+
9 TO SOLENOID IN
12 TO A2

MOTOR Textron 5bc48jb815
S1 TO FNR 3
A2 TO FNR 12
S2 TO B- (Disconnected)
A1 TO R 4

SOLENOID HIGH AMP OUT TO SWEEPER CONTACT

CB1-4 UNWIRED

R1-3 (Resistor pack) UNWired.
R4 to A1

BATTERY IS NOT GROUNDED TO FRAME

KEY OFF - FNR FWD - PEDAL UP
FNR 12 36v
NR6 36v
FNR9 36v
A1 AT R4 0v
S2 0v

KEY OFF - FNR REV - PEDAL UP
FNR 12 36v
NR6 36v
FNR9 36v
A1 AT R4 31v
R3 28.2v
R2 28.2v
R1 30.9v
S2 36v

KEY ON - FNR FWD - PEDAL UP
FNR 12 36V
NR6 36v
FNR9 36V
A1 AT R422v
R4 20.6v
R3 22.8v
R1 22.4v
S2 1.1v

KEY ON - FNR REV - PEDAL UP
FNR 12 36v
NR6 36v
FNR9 36v
A1 AT R4 29v
R3 31.2v
R2 30.0v
R1 29.2v
S2 36.0v

So after all that, with KEY OFF FNR REV I'm still getting 36v between S2 and B-. For the life of me I can't figure out how.

 

[Golf Cart Wizard]

Your wiring is all wrong you have direct battery positive to S1 when in reverse (3 connects to 6) and battery negative to S2 that's a dead short, you need to find a wire diagram to follow

 

[jcloven]

Just for giggles I put my meter between the frame and B- and got 36v. So that's unfortunate. Guess I need to chase that down first.

 

[jcloven]

Your wiring is all wrong you have direct battery positive to S1 when in reverse (3 connects to 6) and battery negative to S2 that's a dead short, you need to find a wire diagram to follow

This is the diagram I'm following.
B+ to FNR9
S1 to FNR12
A2 to FNR3
S2 to B-
A1 to R4

I just disconnected everything (including the key switch and all the micro switches). See attached pictures. I physically removed all the cables from the car.

The ONLY things that are connected are B+ to FNR9 and FNR3 to A2. Somehow I'm still getting 30+v off the frame. If I disconnect A2 it goes away and there is no continuity between the A2 stud and the motor case.

 

[bogman]

Looks like B+ goes to F/R 6 on your wiring diagram to me.

 

[jcloven]

Looks like B+ goes to F/R 6 on your wiring diagram to me.

Correct you are. Thank you for noticing. That was a typo. If you look at the pic I have it on 6.

 

[Rstaley]

Years ago, I drew this diagram for my own use. It may or may not help, but you've definitely got wiring issues. Good luck, Ron.

 

[jcloven]

Years ago, I drew this diagram for my own use. It may or may not help, but you've definitely got wiring issues. Good luck, Ron.
View attachment 12190

I downloaded the book last week. Thank you for that.

I know there are several ways to wire it that will work. I just can't figure out how in the world I'm getting 30+v off the frame and motor case with only one wire connected between the battery and A2. Literally every other wire has been removed. And with that last wire removed there is no continuity between A2 and the motor case or A2 and the frame.

Thank you all for your help and suggestions.

 

[jcloven]

I simplified the circuit even more. I took the FNR out of the equation. I ran B+ to A2 directly. I'm still getting 30v off the frame when grounding to B-. That makes me think that there is an internal short in the motor, but if I disconnect the cable from B+ and test between the cable end, or directly from the A2 stud, and the frame there is no continuity. I'm at a complete loss to explain where this voltage is coming from.

Yet more pics below.

 

[Rstaley]

I think you might be looking at what I call a “phantom” reading caused by the fact that these new digital meters are extremely sensitive and offer a very high impedance of there own to the circuit they are testing. Let’s say that there is a large amount of graphite (from the brushes) built up in the motor. It causes a very high impedance path for current between B+ (A2) that your meter can respond to, even though it would never be “enough” of a path to create a problem. If you were to stick, for example, a 12v light bulb between chassis ground and the point you are testing, it would never light up (the path offers too much impedance to supply enough current to light the bulb)). If you measure with your meter from A2 to the case of the motor with a high resistance scale (not a continuity scale or low resistance scale) like 2M or 20M you will probably get a reading. It will probably be like 10M or even greater. If you were to take the motor apart and blow out all of the graphite dust, it would go away (I done it many times). You may be worrying about something that is never going to be a problem. That’s the only explanation that I can think of. Good luck, Ron.

 

[jcloven]

I think you won the cigar. 30v but zero amps. Now to put it all back together and triple check everything.

So in figure 23 you have B+ KS to MS1 to Solenoid low amp in, solenoid low amp out to MS3 to MS2 and back to the key switch. Am I looking at that correctly?

 

[jcloven]

I think you won the cigar. 30v but zero amps. Now to put it all back together and triple check everything.

So in figure 23 you have B+ KS to MS1 to Solenoid low amp in, solenoid low amp out to MS3 to MS2 and back to the key switch. Am I looking at that correctly?

Scratch that. Me and my typos.

I'm only seeing 2 MSs in figure 23. I have 3. Or am I just not seeing it in the illustration?

 

[Rstaley]

On these older carts I've seen it where people have rearranged the order of the switches, but just so it takes all three switches being activated to get B+ to one of the small connectors of the solenoid and B- to the other one, it will work. Good luck, Ron.

 

[jcloven]

Can anyone tell me the purpose of CB1 having two paths to positive (sweeper contact and cable to Solenoid High Amp out)? Is it just so the motor has immediate power as soon as MS3 closes?

And what would happen if CB1 only had the sweeper contact?

Just curious.

 

[Rstaley]

It would be a disaster. It is terribly important that when the main solenoid makes contact that there is already a path for current BEFORE first speed contact is made. The speed contacts are NOT designed to withstand the initial surge of current in the “take off” mode. This way, when the main contactor makes contact, there is already a path for current flow and all that the speed control does is provide another path and then start to remove resistance as the speed is advanced. If you removed this apparently redundant connection, then the first speed contact would ”fry”, trying to be the path of first contact (surge). If you try it, you will soon be buying a new speed contact board. Good luck, Ron.

 

[jcloven]

It would be a disaster. It is terribly important that when the main solenoid makes contact that there is already a path for current BEFORE first speed contact is made. The speed contacts are NOT designed to withstand the initial surge of current in the “take off” mode. This way, when the main contactor makes contact, there is already a path for current flow and all that the speed control does is provide another path and then start to remove resistance as the speed is advanced. If you removed this apparently redundant connection, then the first speed contact would ”fry”, trying to be the path of first contact (surge). If you try it, you will soon be buying a new speed contact board. Good luck, Ron.

And now I know. You are a wealth of information sir.

 

[jcloven]

Update: It's running!

I replaced the last 2 old cables with new ones that I made myself. So all the wiring is new except for the charging port.

I belive the source of the short was the FNR. The new one did not go back in exactly the same aligned as the old one and I belive it was making contact with the sheet metal. That would explain why it was hot in reverse with the key off and not in forward. Pushing the lever over caused it to shift just enough to touch.

I adjusted it so that there is a gap and when I can I'm going to glue a piece of rubber to the sheet metal to make sure it never contacts again.

I reran the cables in the same order as before and viola, a working cart. I got forward. I got backwards. I even have beeping.

Thank you everyone for helping me think through it.

Two last items. The negative side terminal seems to get pretty hot when running. It's that a common issue and if so is there a common fix.

And finally, sometimes when I let off the accelerator, hot the brake, and then release the brake, it accelerates again. It's that just likely to be something sticking or possibly the ball socket being out of adjustment?

Thank you again everyone!