Overdrive electrics
 

My '50 Merc is 12 volt - ground, with Painless wiring end to end. This week I removed the defective 12 volt overdrive solenoid and re-installed the original 6 volt to fill the void until I can get a new 12 volt.

Today I drove the car about two blocks when the car quit cold. Turns out the 30 amp fuse in the COIL slot blew. I replaced the fuse, and got a repeat performance.

I'm using a traditional Ford overdrive relay, (three posts) and have a #10 wire running from the relay fuse to the + coil terminal.

Any ideas why I'm blowing that fuse? I'm stumped.

Re: Overdrive electrics
 

Have you reduced the voltage to the solenoid to 6v?

Re: Overdrive electrics
 

Disconnect the solenoid and see if it still blows the fuse.

Re: Overdrive electrics
 

So 12 volts and half the amps of the 6 volt system. What is the 'coil slot'?

Re: Overdrive electrics
 

By "coil slot" I was referring to the slot in the Painless fuse panel that holds the 30 amp fuse. .... that's the label on that slot.

I drove the car using the 6V solenoid for a few months without any problems before buying a 12 V solenoid. I'll try driving it without activating the 6 V solenoid... see wht happens. I ran out of time Friday.... and frankly got lucky.... the fuse blew just a few blocks from where I started, and I was able to coast (backwards) downhill to my starting point. (did I mention? The car quit dead when the fuse blew).

Re: Overdrive electrics
 

I’ve run a 6v solenoid on 12v for years without trouble (knock wood)

Re: Overdrive electrics
 

The OD should work with a 6v solenoid. But things happen. The OP is going to have to troubleshoot the cause of the excessive draw. The solenoid was the last thing he did from his description. It could be the solenoid, wiring, kickdown switch, or nothing connected to the OD and wiring. I would disconnect the solenoid from the wiring first. Then I would take the OD feed off the coil. If it still blows the fuse, he has some more diagnostics to do. Is his 12v solenoid actually defective, or something related to this issue?

Re: Overdrive electrics
 

Blowing a 30-amp fuse in succession indicates a direct short to ground somewhere. Check all the wiring to make sure it's not grounding out anywhere. The fuse is for the protection of all the wiring but the main circuit is the operating circuit. Kick down is a separate circuit but is part of the complete circuit for operation in all modes.

The coil doesn't need a 10-AWG wire to ground it out when you hit the kick down switch. A 16-AWG would suffice. The solenoid operating circuit can get by with smaller wire on 12-volts. Does this transmission still have a rail cut out switch or has it been removed? My early 51 cars still have them but they have to be maintained or bypassed. Does it blow the fuse when in overdrive or just when you try to kick it out of overdrive? There is a point set in the solenoid that controls the coil grounding function in kick down and there is a point set that controls the switch from the overdrive pull in coil to the overdrive hold in coil function. The pull in function is a high amp function so it needs to go into holding function as soon as it's in overdrive so as not to pull too many amps. The kick down switch is in a swampy area so it has to be maintained in good condition as well. The governor is there to keep the unit from going into overdrive below 25 MPH or so. They can get a build up of crud in the points now and then but the overdrive usually just doesn't function if the switch isn't working right.

Make sure the operating solenoid is properly connected too. It can sometimes be something simple like that. We all make mistakes now and then. I know I have. A Link:
https://fifthaveinternetgarage.blogs...ve-wiring.html

Re: Overdrive electrics
 

The kickdown switch, relay, and 12 volt solenoid are all new, as is the wiring, which I continuity-checked yesterday. Found out the hard way the 12 volt solenoid is defective. The shaft on the solenoid has a "knob" on the end (flat on two sides) that fit into a slot in the pawl inside the overdrive unit. On my new solenoid the knob is oversized. It will fit through the opening in the pawl, but when turned, it binds in the larger opening in the pawl. Anyway, that's why I re-installed the 6 volt solenoid

The #10 wiring is overkill, but what I had available at the time.

I did bypass the rail switch. Wire is direct from the governor to the kickdown switch. Governor has been tested, and appears to close about 25 mph... a little below the pre-determined speed.

I will try Monday to drive the car with the solenoid out of the circuit.

Thanks all for the suggestions.

Re: Overdrive electrics
 

UPDATE:

Drove the car with the solenoid out of circuit, and no blown fuses. Also checked all circuits (again). Found no obvious shorts.

I made one wiring change, switching the wire to the IGN terminal on the overdrive relay from the coil + terminal to the IGN terminal on the key switch. I then put the solenoid back in the circuit, and low and behold..... my overdrive is working--- and no blown fuses. Drove about 10 miles late this afternoon, with several stops and starts, and it went into overdrive like it was new. Now if I can get a new 12 volt solenoid before the 6 volt gives out.

Jackson

Re: Overdrive electrics
 

Glad you found it. You are getting a good Borg Warner electric overdrive education. My old Mercury cars taught me a lot about them.

Re: Overdrive electrics
 

Without this forum I doubt I would have ever gotten my overdrive issues fixed. The wisdom of forum participants like yourself, and their wilingness to share is a blessing.. and I'm grateful.

A shoutout to Mac at VanPelt. He helped me with parts and suggestions that helped me replace the gear/balk ring and the rail/fork assembly.