74 fj40 coil wiring

[nick1860]

My 40 came without a coil or resistor and wanting to know what wires go to the resistor and which ones go to the + side of the coil and what ones to the - side. The wire diaghram I keep finding for it does not show a resistor or what sides of the coil is which

 

[Roboosfj40s]

Hey Nick, There should be a black/yellow wire coming from the ignition circuit (ignition sw.) This wire goes to the Ballast resisitor Primary then the same color from the Secondary side of the res. to the Positive+ side of the coil. From the Negative- coil side to the distributor. Now this is providing you are using an external resistor coil. If using an internal resisited coil the hook up it the same just no Ballast resisitor inline. Hope this helps!

Rob

 

[Rocky_LC]

IIRC, there is also a wire that comes off the starter solenoid that provides you a shot of "non-resistied" 12V when the solenoid is engaged. This wire is only active with the starter on.

The wire comes off the little tab on the starter solenoid, and goes to the (+) side of the coil.

Rocky

 

[nick1860]

thanks guys.

 

[nick1860]

have it wired up this way and something is fishy. Just for kicks I put a push button from battery to starter and the engine tried to fire without the key on. I have the black with yellow stripe to the + side of resistor and the other side of the resistor to the + side of the coil where also the black with the white stripe is that goes to the starter. Then the black wire goes to the dist am I missing something

 

[Roboosfj40s]

have it wired up this way and something is fishy. Just for kicks I put a push button from battery to starter and the engine tried to fire without the key on. I have the black with yellow stripe to the + side of resistor and the other side of the resistor to the + side of the coil where also the black with the white stripe is that goes to the starter. Then the black wire goes to the dist am I missing something

The wire that goes to the starter solenoid should come from the ignition switch and to the starter only. The push button is doing the same thing as a remote starter switch, a cheap mechanics tool. I have one lol. Remove the blk/wht wire from the starter to coil and try it again. Should be only at least on my truck; Blk/yw to resistor from resistor to +coil. From - coil to dist.

 

[Rocky_LC]

...I put a push button from battery to starter and the engine tried to fire without the key on.

Then you must have sent power directly to the solenoid (bypassing the ignition switch), which will crank the starter, and when the solenoid gets pulled in, it sends voltage to the + side of the coil, which will let the engine run as long as the starter is cranking.

Let me guess.... As soon as you stopped cranking the starter, the engine died?

Rocky

 

[nick1860]

Yes Rocky that is what happened so does that mean I had it wired correct the first time

 

[bikersmurf]

If all is wired correctly, and it starts when you turn the key, but dies when you let go, the ballast resistor is shot.

Can you test the ballast resistor? If you run a jumper from one side to the other, does it run?

 

[Rocky_LC]

Or just take a meter across the ballast resistor. Bikersmurf is right about jumping it (but don't run like that, or your coil can overheat). His solution is the easiest way to check it.

If you take it out of the circuit (disconnect the wires), with a meter (set on "Ohms"), you should get show a pretty low resistance (I am guessing about 3 Ohms, but maybe I am wrong). You definately should NOT see an "open circuit" (infinite).

The purpose of the Ballast Resistor is to cut down the voltage that the coil sees under general operating conditions. The ballast resistor drops about 5 Volts (I think the coil runs at 7 volts normally). The purpose of the wire from the solenoid is to give the coil the full 12V when you are cranking the engine (resulting in a hotter spark at startup).

Good Luck

Rocky

 

[Pin_Head]

There is a diagram for a 78 in tech links that shows how to wire it. The ignition coil wiring on your '74 is the same. The ballast resistor is the zig zag part of the wire that is black with yellow stripe. The color code of the wire from the ignition switch to the starter motor has the wrong color code in the diagram. The real color of this wire is black with white stripe.

http://www.ih8mud.com/tech/pdf/fj40_wiring_diagram.pdf

 

[nick1860]

thanks for the schematic I better save that. Hoping I can get out and work on it this weekend thanks again guys

 

[pc4400]

Anyone know what resistance for the ballast resistor?

I found 3/4 ohm, 1 ohm and 1-1/2 ohm

 

[nick1860]

Well after alot of cussing and a few beers I found I had a bad fuse that would test ok with the door open but when it shuts the fuse end I guess would loose contact to the black and yellow wire causing it not to start. Now all new fuses and got to take it out in the yard with no brakes . Now on to the next step

 

[Pin_Head]

That is pretty strange because the ignition circuit on FJ40s of that vintage is not fused at all. Maybe it is wired incorectly?