Wiring issue

[JD39B]

I have a mm RTU. 1948 with a distributor. Push pull on off
switch. Will start by hand but will not start with the starter.
Every time I use the switch it cuts my spark out. Have new
push switch. New ignition switch new amp gauge new 6 v
coil and new solenoid. What am I missing. Trying to get it to
go with the old 6 v system. The p.o had it on 12v and had
wires all connected with screws to make it run. It looked
bad so Im trying to go back to factory. Thanks in advance
from a 2 cyl guy used to a 2 spark plug wiring harness

 

[Janicholson]

Low voltage at the coil is likely the issue. Several things can be involved. Maybe more than one.
A battery that has a volt reading of 12.4 (not running)is not charged enough, or is weak. Small 12v cables. The Copper needs to be 3/8 inches thick, 0-gauge. The starter motor needs to draw 200 amps or less while cranking. There are gauges for this. Starters can drag internally from worn bushings. Poor connections or internally corroded cables. All these things can drop battery volts below the threshold of spark.
Hand cranking allows full volts to the coil. Jim
one source many others

 

[Hemmjo]

I have never worked on an MM RTU so this is a generic response. Very possible when using the starter, the voltage drops too low to make a spark. A lot of older systems used an external resistor to the coil when the engine was running. When starting here was a circuit to bypass the resistor to account for voltage drop from the starter.

 

[DPittman]

I dont know what you mean by cuts the spark out but I had the same problem with a 50 RTU. Had power to the coil and it would start by hand crank but push the starter button it would kill the power to the coil. Replaced the battery cause it was only 9 years old and tired anyway, bench testing the starter and solenoid proved them good.
Keeping all my other frustrations to myself it turned out to be a bad battery cable. It was strong enough for the ignition but wouldnt pull enough power for the starter. Had to wiggle it under load to find that out. Felt kinda silly cause it appeared to be fine but looks can be deceiving DP

 

[JD39B]

So I have correct 0 gauge wire for the ground and hot cable. All new wire on the connectionsBUT I switched back to the 12v battery and coil with my wiring and it took right off. Looks like the old starter may be the draw on power. Thanks for helping. My next decision will probably be to switch to a 12v generator and light bulbs.

 

[boler76]

personally I would fix it so it works properly on 6v

 

[BarnyardEngineering]

Did you by chance leave the ballast resistor in for the coil, or use a "no external resistor required" 12V coil?

 

[BarnyardEngineering]

(quoted from post at 04:33:53 10/09/23) personally I would fix it so it works properly on 6v

Easier said than done. Hard to find a good starter shop these days, and there may not be anything wrong with the starter to begin with.

That tractor's likely been overhauled multiple times, probably with some kind of overbore piston and sleeve, one or more head shaves and/or block planes. Takes a lot more to wheel it over than when it was new.

 

[timcasbolt]

(quoted from post at 06:33:53 10/09/23) personally I would fix it so it works properly on 6v

f it's for show, I would agree. If it's for everyday use, I'd switch it to a 10si and 12v.

 

[560Dennis]

Suggest a voltage drop test ,may be something simple as poor ground , cable ? Tell a lot that way .

 

[Born Again Green]

(quoted from post at 10:33:53 10/09/23) personally I would fix it so it works properly on 6v[/



Since you guys are recent, Would anyone have a wiring diagram for a 1978 Ford Diesel 3600

 

[showcrop]

(quoted from post at 14:56:15 10/09/23)

(quoted from post at 10:33:53 10/09/23) personally I would fix it so it works properly on 6v[/



Since you guys are recent, Would anyone have a wiring diagram for a 1978 Ford Diesel 3600

Recent? maybe. Maybe not. but anyway you may get answers if you drop down to the JD forum and put in a new post, rather than adding onto one on a different topic.

 

[Born Again Green]

(quoted from post at 21:12:36 10/09/23)

(quoted from post at 14:56:15 10/09/23)

(quoted from post at 10:33:53 10/09/23) personally I would fix it so it works properly on 6v[/



Since you guys are recent, Would anyone have a wiring diagram for a 1978 Ford Diesel 3600

Recent? maybe. Maybe not. but anyway you may get answers if you drop down to the JD forum and put in a new post, rather than adding onto one on a different topic.

JD as in John Deer ???

 

[Born Again Green]

JD as in John Deer ? I'm not sure where to navigate ? JD doesn't jingle dong right with this harness of wires

 

[JD39B]

Found a dead spot on the starter so that is most likely the
culprit. I have a couple extra good started around I can try
to use.

 

[Jim.ME]

(quoted from post at 18:28:35 10/09/23)
JD as in John Deer ? I'm not sure where to navigate ? JD doesn't jingle dong right with this harness of wires

Yes, JD would be for John Deere. You are looking for info on a 1978 Ford Diesel 3600, correct?

Here is a link to take you to the Ford Forum this site has. You will likely have better luck there. Start a post with all the info and issuse with your tractor.

Ford Discussion Forum

 

[JD39B]

The coil used with the 6 volt battery was a 6 volt but the 12v
coil used with the 12v is a non ballast coil

 

[JD39B]

Thats still the idea moving forward. Clearly there is something at play here and it is not the wiring.

 

[JD39B]

This is exactly what is going on with mine. The problem is the cables are nice new thick ones.