Lost voltage to coil while cranking

O

Owlseye

Member
OK maybe I am beating a dead horse, but I seem to lose most of the voltage to my ignition coil during cranking with the starter. I have run 0 and 00 cables to ground and starter. I have cleaned the connections on the battery, frame, engine, and starter switch. Also replaced the foot starter switch due to burned contact bar. I have checked voltage to points and coil while the engine is not running or cranking and I have 6 volts as long as the points are open. Voltage to coil while cranking drops to 2 volts or less. I have also replaced the starter thinking that it may be drawing too much current. How do I get better voltage to the ignition while starting? As it is the truck is a bear to start. Can anyone give me any ideas? THANKS.
 
Hi,

If the engine is cranking at close to a normal rate,the voltage at the starter while cranking should be near normal so, if you're seeing 2V at the coil, I would suspect an internal partial short in the coil. Try swapping in a known good coil.

Hope this helps
 
Well I would think that the very first thing to do is test the voltage at the battery at rest and then while cranking the engine. Or better still have the battery load tested by placing about 300 plus amps load on it while measuring the voltage. Even if the battery is new it should be load tested. After establishing that the battery is good you can move on further along the circuit and voltage test. Regards, Kevin.
 
Put one terminal of a volt meter on the hot terminal of the battery. That would be on the battery post itself. Then, put the other terminal on the clamp and crank the engine a bit. If it shows voltage, your clamp / battery joint needs to be cleaned. if no voltage shows, move the meter terminal to the other end of the cable, cranking the engine at each point. Does it show voltage? Do this at every point to the starter. If that half of the starter circuit shows very little drop, start again at the ground side battery terminal checking all points to the starter itself. You seem to have a bad joint somewhere along the line. Something like a loose connection or paint on a ground.
 
Charge up your battery and take it to your local auto parts store to have it load checked. It's free of charge. Many battery's fail under loaded conditions only.
 
get a 10 amp or larger dioed. now run a wire from the starter side of sol. on the fire wall to one side of the dioed flow toward coil. run wire on flow side of dioed to coil. now when you hit the starter you will get full volatge to coil. the dioed will prevent back feed to the sol.when truck starts
 
Richard, 1933 does not use a solenoid. It uses a heavy contact foot switch, so you manually make the connection to the starter. I am leaning toward the voltage resistor as maybe the problem. What happens if I bypass the resistor ad what does it do on a 6 volt system? No gauges are fed off of the power, all are mechanical.
 
Marko39 , what does the resistor do o a 6 volt system? Yes I have one right beside the fuse block. What is it dropping the current to? All gauges are mechanical. If I take the resistor out of circuit and bypass it what will that do?
 
The resistor drops the voltage to the coil. Not sure what coil you are using but you should have 6volts entering and about 3 volts going to coil. This is easy to test and if bad look for a nos resistor.
 
With resistor bypassed you should have 6volts to coil. You should not run it very long with it bypassed
 
6 volt starters require a huge current to crank. (That's one of the reasons that everyone went to 12 volt systems.) With that large current, the slightest resistance in any of the connections or cables in the starting current loop will cause a large voltage drop. You have to check for voltage drops all along the way, both the "hot" side and the ground side.
 
I don't think you would need a resistor with an 8BA. Was the truck originally
a V8 or a 4 cyl, the 4 cyl didn't us a resister.
 
If it is a "can" style coil, it has to have 6 volts to the coil (no ballast resistor). It is simple to bypass the resistor, just move the input wire to the output side so both wires are on the same side of the resistor. You can check the coil to determine what you have, the resistance across the two terminals should be around 1.5 ohms. If that is what you have, no resistor should be used in the circuit.
 
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