93 Marathon 36V doesn’t move

[jhughey79]

I’ve been reading this forum quite a bit and I haven’t found my solution yet. Here’s where I’m at:
I have a 93 Marathon 36V. The cart measures 36.8V with the key on in neutral. Once I shift it to forward or reverse, the voltage at the controller drops to 30. If I hit the gas pedal, it jumps back to 36.4 but does not turn the wheels. As soon as the pedal is released, voltage dips back to 30. The solenoid clicks when I hit the pedal.

Back story: this cart had a 500amp Curtis controller. The FNR switch was melted and the cart wouldn’t move. I replaced it, and all of the micro switches. They all show voltage going through when engaged. I then replaced the POT box. Nothing changed. Replaced the controller with a 325amp Curtis controller. No change. I have taken pictures of all wiring as I’ve done work to make sure I’m getting things back where they should go, and from what I can see everything is correct.

What are my next steps? This thing has almost new everything…when I bought it it had a newer motor, and it ran really well. It would go about 20, albeit it wasn’t super torquey which is probably expected of a 36V cart. Any tips would be greatly appreciated.

[jhughey79]

Update if anyone reads this…replaced the diode on the solenoid. It blew immediately when I touched the go pedal.

Also…when I replaced the POT box, it came with red and black wires instead of white and black. I put the black in the same place as the previous black wires, and red where the white had been.

[jhughey79]

Replaced the diode (correctly this time). The solenoid clicks as soon as I shift into gear, but the wheels do not turn. Micro switch on the POT box bad, maybe? It shows 36.5V on both sides of the switch after shifting into gear, prior to touching the go pedal.

[scottyb]

The pot MS should be powered by the key (power on one side) and triggered by the pedal (power at both sides)
Many of the Pots available have 3 terminals on the ms. use your continuity meter to determine which 2 terminals are normally off then on with the switch. Note there is a combination of 2 of these 3 terminals that is on constantly then off with the pedal.
This may be your problem > being on the wrong switch terminals.

If memory serves me right, and it does not always, you want to be on the 2 outer terminals with the center empty

[jhughey79]

Well, that MS was bad. Replaced it with a new one. Still no wheel movement, so here’s a bunch of voltage readings that I hope help with my troubleshooting:

Key off in N
Pack 36.4
Solenoid controller side 35.9
FNR 1 35.9
FNR 2 24.4
FNR 3 0.0
FNR 4 24.4
Pot MS 0 on both

Key on in N same as above

Key on in F no pedal
Controller drop to 30
FNR 1 30
FNR 2 24.4
FNR 3 13.3
FNR 4 24.4

Key on in R no pedal
FNR 1 30
FNR 2 13.3
FNR 3 13.3
FNR 4 13.3

Key on in F with pedal depressed
Controller 36.4
FNR 1 36.4
FNR 2 36.4
FNR 3 13.3
FNR 4 36.4

Key on in R with pedal depressed
Controller 36.4
FNR 1 36.4
FNR 2 13.3
FNR 3 13.3
FNR 4 13.3

[jhughey79]

Would it be possible that the resistor on the solenoid is bad? Since I have a drop of 6 volts and I keep reading that it shouldn’t be more than 3, it makes me think that’s causing the issue. But I end up with pack voltage after pressing the go pedal…which doesn’t make sense as to why the wheels won’t turn.

[SolarRat]

I know nothing about this particular cart, and don't have a diagram in front of me...but 36.4v is dead. I'm not sure if that controller has a low voltage cutoff, but 35.9v at the solenoid is just pain dead and not charged enough for any proper testing. Any draw at that point would bring it down an easy few more volts. Do they not hold a charge?

It might not be your actual problem, but it sounds like you have a bad battery or a very bad connection on one or more battery terminals. If so, any testing may not give reliable results.

[SolarRat]

Originally Posted by jhughey79

Would it be possible that the resistor on the solenoid is bad? Since I have a drop of 6 volts and I keep reading that it shouldn’t be more than 3, it makes me think that’s causing the issue. But I end up with pack voltage after pressing the go pedal…which doesn’t make sense as to why the wheels won’t turn.

No. The resistor just pre-charges the capacitors in the controller. The only ways you could have a 6v drop are bad batteries, bad connections, or something is shorted. The latter two would cause a LOT of heat, so feel around. When you have this 6v drop, put a volt meter on each individual battery...see if they drop the same.

[jhughey79]

Thanks! I charged the batteries but haven’t started testing again. I’ll do some checking…thanks for your assistance!

[Buzzworth]

Rotary switch (FNR) ? Check that you have continuity across the terminals. I just found that my terminal A was burned and did not make contact. I had to remove the switch and take it apart to find the problem.