How much current does a coil need?

desertrat

desertrat

0_0
70 Ford pickup. No spark. No 12v to coil so wiring or unfound fuse or does it go through a relay? I figured hooking 12v outside source to it may work, but don't want to burn it up. (New coil). I know some have or had internal resistance to limit current or resistive wire going to them. This is just regular wire though.
 
GWguy

GWguy

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Foreign cars would have a resistor mounted on the firewall just prior to the coil. Some US vehicles did too, not sure if Ford ever did. I know my '63 Belair did.

See if you can find a wiring diagram on line for the truck and look for a resistor before the coil. If none, it's OK to run a hot directly to the coil.
 
GWguy

GWguy

*
The diagram may also contain a reference to a "fuseable link". It's a kind of resistive wire which pops under load.
 
PJumper

PJumper

New Member
desertrat said:
70 Ford pickup. No spark. No 12v to coil so wiring or unfound fuse or does it go through a relay? I figured hooking 12v outside source to it may work, but don't want to burn it up. (New coil). I know some have or had internal resistance to limit current or resistive wire going to them. This is just regular wire though.
Click to expand...


There should be a Start Relay in between the battery and the coil. When you turn the ignition key you should hear an audible click and have the 12 V available at the coil. If no click is heard, check Ignition fuse. If fuse is good, then it's your relay (common problem). You could also do internet search for the Make/Model/Year of your truck and type the problem.
 
desertrat

desertrat

0_0
PJumper said:
There should be a Start Relay in between the battery and the coil. When you turn the ignition key you should hear an audible click and have the 12 V available at the coil. If no click is heard, check Ignition fuse. If fuse is good, then it's your relay (common problem). You could also do internet search for the Make/Model/Year of your truck and type the problem.
Click to expand...

Yeah the relay is going to get checked next.

glhs837 said:
Hmmm, looks like the ballast resistor for a 70 F100 is actually a wire looking thing.

70 1970 Ford F100 Pickup Ballast Resistor - Engine Electrical - Standard Motor Products - PartsGeek
Click to expand...

Not seeing anything like a resistor or other than regular wire. Good chance a few things have been changed on this truck.
 
Gilligan

Gilligan

#*! boat!
PREMO Member
desertrat said:
70 Ford pickup. No spark. No 12v to coil so wiring or unfound fuse or does it go through a relay? I figured hooking 12v outside source to it may work, but don't want to burn it up. (New coil). I know some have or had internal resistance to limit current or resistive wire going to them. This is just regular wire though.
Click to expand...

That year would have used resistor wire in the harness coil feed, dropping the voltage to about 7.5V at the coil. The coil resistance would be roughly 1.5 ohms on the 12V side...possibly less. Hitting a Ford coil with the full 12V (which is what the "I" post on the starter solenoid does when you are cranking the engine) for more than a brief period will burn it up. However, you can "get away with juicing the coil directly with 12V " for a short period of time as a "get home" hot-wire measure as long as you do not leave the 12V on the coil for anything but a very brief period of time when the engine is not actually running.
 
Gilligan

Gilligan

#*! boat!
PREMO Member
desertrat said:
Not seeing anything like a resistor or other than regular wire. Good chance a few things have been changed on this truck.
Click to expand...

The Ford ballast wire looks the same as regular wire. So does the new resistor wire.

The stuff will eventually give out.

You can run a new ignition wire from the switch with regular wire and insert a Chrysler ballast resistor in line with it.
 
aps45819

aps45819

24/7 Single Dad
Hook one side to the battery, hold the other and pee on the bumper.

It's now easy to tell if it works
 
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