Merc OD

P

Pvmt-Pndr

Member
1950 factory merc, 3 on the tree with OD, 6V. I replaced all the wiring within the system. I found that my kick down switch is in question now. My main question is what side of the coil does the "interrupter wire" connect to? + or -? And which wire goes where on the actuator on the trans? I just took it for the first ride after going through the system and that's what I wasn't confident in. The whole system isn't in the prettiest of shape but I'm managing. Thanks
 
Last edited:
Ok, Lets go slow here and I think I can walk you through this, The answer to your first ? is the distributor side of the coil. This grounds out the points for a millisecond and allows the overdrive to disengage. The actuator as you call it is I assume the solenoid ( round thing about the size of a beer can on the drivers side) It gets power from the relay on the firewall through the kickdown switch. The second wire should go back through the kick down switch to the point side of the coil. You can test which is which on the solenoid by putting power to them one at a time. The one that make it click is the power. The wire that goes to the speed switch on the passenger side is the actuator wire for the relay on the firewall. I hope this helps ,Tim
 
Wiring diagram for the OD is attached.
 

Attachments

  • Overdrive Wiring Diagram.jpg
    Overdrive Wiring Diagram.jpg
    17.5 KB · Views: 327
It would connect to the points side. With positive ground that should be the + terminal but I keep a polarity tester in my tool box just in case. If it grounds the power side the a wire will get real hot real fast.
 
Thanks a lot guys! I think I have it wired correctly but will check this weekend. I bought the wiring from shoebox central. I have no idea if there is an electrical gremlin in the system because it hasn't work since I got it and I found the original wires cut, taped and stuffed by the trans.
 
rotorwrench said:
It would connect to the points side. With positive ground that should be the + terminal but I keep a polarity tester in my tool box just in case. If it grounds the power side the a wire will get real hot real fast.
Click to expand...


Hmmm, Rotor you bring up a point that had escaped me in my converting from 6v - 12v neg. ground in my '51. The points side of my dist will be neg terminal of coil yes?
 
I'm a little late but your reasoning is correct for negative ground. I still check polarity with the Nu-Rex sparklite tool.
 
All the wiring is factory-ish on the car. I have rewired everything under the hood at this point, 6v positive ground. I did buy a modern 6V wiring harness to replace all of the wiring in the car, that's one of my big jobs for this winter. The weather here (Michigan) has been nice enough to drive plus I got the heater working a couple weeks ago and made a complete exhaust for it, now I can drive with the windows up since no fumes come into the car. I haven't really dug into the car yet for my winter plans. So I've been taking advantage of making improvements and still being able to test. My plan today is to correct any wiring in the OD that may be wrong and then drive it around. 55-60 mpg with no OD it's working hard. I've ran 2 tanks of gas through it over the summer with minimal idle time and have gotten 7 and 10 mpg.
 
Last edited:
Pvmt-Pndr said:
I've ran 2 tanks of gas through it over the summer with minimal idle time and have gotten 7 and 10 mpg.
Click to expand...
That is unusually bad gas mileage for a load-o-matic era flathead. Without overdrive I'm used to seeing 15 mpg on worn but not worn out engines. Have you checked if the vacuum advance unit is good?
 
I checked the vacuum advance once I got it running about 6 months ago, it does work. It may not work correctly for now, thanks for reminding me. I need to replace the vacuum line. I also have an average of 105-ish psi per cylinder when I did a compression test.

As for the OD I verified all wiring is hooked correctly, every wire within the system is brand new now. It's not working though. I put power to the solenoid on the trans and it clicked. I also put power to the relay under the hood, it also clicks. I believe my kickdown switch is bad, it isn't in the best of shape. Aside from that I see no electrical reason for it not to work. Am I correct to think that the kickdown switch can stop the OD from working?

Currently with my OD engaged I get the typical free spinning. Once I replace the kickdown switch it'll either work or it won't. If it doesn't I'll go back through all the threads I've read and start verifying everything is correct on the trans.

Side note. I replaced my speedometer cable today also because the old one was making all kinds of noise and jumping around. Under 30 mph the new one is nice, quiet, smooth and reads correctly. Over 30ish mph it was worse than before! I had to disconnect it in a parking lot just to hear if my OD was kicking in or not.
 
Last edited:
If you want to test the overdrive by itself you can bypass the factory controls. Run a jumper wire to a switch that you can reach from the drivers seat to power the solenoid. The crudest version of this I ever did was run a hot wire to the passenger area and a second wire run through rust holes in the floor to the solenoid with an alligator clip. Dad drove and I clipped the ends of the wires together when it was time to test the overdrive.


Have you checked that the points in the governor are working? If the points in there are dirty you don't get a connection and the overdrive doesn't drop in.
 
The points are in the cap that was removed from the governor body you are holding. When you spin up the shaft in the body in your hand the center shaft moves towards the cap and closes the points to complete a ground circuit. Picture 1439 shows the point side of the cap. To test the governor function put the cap back on and connect an OHM meter between the 2 terminals shown in picture 1479 9there are multiple designs of the cap but they function similarly). With the drill attached and not turning you should have and open circuit. When you spin up the shaft and reach the proper rpm the circuit should be completed.
 

Attachments

  • IMG_1439.jpg
    IMG_1439.jpg
    34.5 KB · Views: 7
  • IMG_1479.jpg
    IMG_1479.jpg
    31.1 KB · Views: 7
A couple of more pictures.

Where are you in Michigan? I am just west of Detroit (Livonia). I have a test jumper harness that I made to get my OD working. I found 2 issues, My governor wouldn't engage until 40 mph rather than 27 mph. And I had a voltage drop issue to the relay (fixed by running a wire directly to the relay bypassing the ignition switch).
 

Attachments

  • IMG_1457.jpg
    IMG_1457.jpg
    21.3 KB · Views: 6
  • IMG_1490.jpg
    IMG_1490.jpg
    44.1 KB · Views: 6
Temperance MI, just north of toledo.

Duplicating the test I'm seeing as high as 12 ohms while spinning my drill max rpm. An open circuit when not spinning
 
What would be the proper way to bypass the kickdown until I get another one? This is the wiring diagram and I have dug up.
 

Attachments

  • 20231216_162806.jpg
    20231216_162806.jpg
    25.6 KB · Views: 15
You must log in or register to reply here.
Back
Top