The Ford Barn

mjdunn · 07-10-2016, 12:48 PM

My 1939 Ford runs perfectly until I turn on the headlights or the electric cooling fan on the radiator, and then it starts missing out. I have running lights that also come on at the same time the headlights come on. It is still 6 volt and I have a 6 volt alternator and an Otima Red top battery. I assume this is caused by too much draw on the electrical system. Have any of you had a similar problem? If so, is there anything I can do to remedy this?

RKS.PA · 07-10-2016, 01:11 PM

Not sure about this, but with all your lights, fan, etc on, check the voltage output from your alternator. Think it should be in the 7.2 to 7.4 range. Also, can you trouble shoot for any shorts in any of those circuits.

I have a '39 with all those electrical extras, 6volt Optima, and alternator and I don't have any of those issues.

Good luck....Dick.

rich b · 07-10-2016, 01:48 PM

If the alternator output checks out, I'd check out connections down the line for the voltage drop. If an existing system that was working, watch for corrosion, loose or overheated terminal crimps and connectors, etc. If this is a new set-up be sure wires are sized for
a six volt system. Relays for the fan and lights can be used to "unload" the main wiring harness and switches if that is the source of the drop.

mjdunn · 07-10-2016, 02:41 PM

Thanks guys. The last time I checked the alternator it checked out OK, but I will check it again. I have relays on the fan and the lights. I will check the voltage going to the distributor, with the fan running.

Ken/Alabama · 07-10-2016, 03:00 PM

Also check the contacts inside the ignition on/off switch on the column.

BUBBAS IGNITION · 07-10-2016, 03:10 PM

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I see this quite a bit . Some of the electric fans draw way too many amps and hurt the ignition supply voltage. I had one ( dual set) last summer drawing almost 70 amps ! Drops the ignition voltage when on ,your six volt system when running has approx 3-4 volts to the coil after the dash resistor . Check voltage at the coil input driving with fan on........

koates · 07-11-2016, 02:23 AM

Yes that's right ! A 6 volt radiator fan can draw over 25 amps. Plus all your lights on which could total up to well over 50 amps draw on your system. Your ignition circuit is being robbed of voltage because of this EXTRA HEAVY draw. Do some testing with a test ammeter on the actual current draw on each circuit. Check the voltage at the ignition coil with everything turned on and engine at some revs. Voltage at coil should not go below 3.5 volts at a minimum. Use a heavy gauge wire (#10) to feed your radiator fan via a 30 amp relay direct from the battery terminal on the starter solenoid. Even with a 6 volt alternator the system was never designed for these type of loads all on at the same time. Make sure the alternator battery wire is at least # 8 gauge but depends on the amps rating of the alternator. Everything in a 6 volt system has to be correct and most are not up to scratch. Regards. Kevin.

G.M. · 07-11-2016, 07:00 AM

Check the voltage to the coil when the engine is running, it should be about 4.0
volts. Turn your fan on and read the voltage and I'll bet it's 3.0 volts or lower.
Look for a bad battery or ground connection. G.M.

JSeery · 07-11-2016, 07:26 AM

Also, what is the rated amp output of your alternator? Is it even designed for this much current draw?

Henry/Kokomo · 07-11-2016, 08:02 AM

Check how the car is wired. I think there's a good chance that rich b (post #3) is on to a solution I'd also be wary of putting too many amps through the ignition switch as well.

JSeery · 07-11-2016, 09:29 AM

There really should not be anything attached to the ignition switch other than the ignition coil and the dash instruments. Relay trigger wires might be ok, but that is about it.

scooder · 07-11-2016, 03:39 PM

It sounds like a possible wiring issue, this is only based on RKS.PA stating he has the same stuff but without the miss. It could be your fan is a higher amp than his though. So check your voltage as above. Definitely agree with the relay with power direct from battery.
Not trying to be cocky here, a mechanical fan uses no amps.
Martin.

mjdunn · 07-11-2016, 05:33 PM

The only thing running through the ignition switch is the trigger switch for the fan and the lights. The fan and lights are running straight off the battery through a relay. They are separate relays. The alternator is putting out 7 volts. The wire going to the fan is a 10 gauge wire. The wire from the battery to the relay for the lights is also 10 gauge.

07-10-2016, 01:11 PM	#2
RKS.PA Senior Member Join Date: Jun 2010 Location: Marana, AZ Posts: 1,194	Re: Misses out when the cooling fan is on Not sure about this, but with all your lights, fan, etc on, check the voltage output from your alternator. Think it should be in the 7.2 to 7.4 range. Also, can you trouble shoot for any shorts in any of those circuits. I have a '39 with all those electrical extras, 6volt Optima, and alternator and I don't have any of those issues. Good luck....Dick.

07-10-2016, 02:41 PM	#4
mjdunn Senior Member Join Date: May 2013 Location: Dry Ridge, KY Posts: 107	Re: Misses out when the cooling fan is on Thanks guys. The last time I checked the alternator it checked out OK, but I will check it again. I have relays on the fan and the lights. I will check the voltage going to the distributor, with the fan running.

07-10-2016, 03:00 PM	#5
Ken/Alabama Senior Member Join Date: May 2010 Location: Alabama Posts: 3,257	Re: Misses out when the cooling fan is on Also check the contacts inside the ignition on/off switch on the column.

07-10-2016, 03:10 PM	#6
BUBBAS IGNITION Senior Member Join Date: May 2010 Location: SPEEDWAY INDIANA Posts: 4,148	Re: Misses out when the cooling fan is on Sponsored Links (Register now to hide all advertisements) I see this quite a bit . Some of the electric fans draw way too many amps and hurt the ignition supply voltage. I had one ( dual set) last summer drawing almost 70 amps ! Drops the ignition voltage when on ,your six volt system when running has approx 3-4 volts to the coil after the dash resistor . Check voltage at the coil input driving with fan on........ __________________ If it Makes Spark, we do it !!!! www.bubbasignition.com [email protected]

07-11-2016, 02:23 AM	#7
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,078	Re: Misses out when the cooling fan is on Yes that's right ! A 6 volt radiator fan can draw over 25 amps. Plus all your lights on which could total up to well over 50 amps draw on your system. Your ignition circuit is being robbed of voltage because of this EXTRA HEAVY draw. Do some testing with a test ammeter on the actual current draw on each circuit. Check the voltage at the ignition coil with everything turned on and engine at some revs. Voltage at coil should not go below 3.5 volts at a minimum. Use a heavy gauge wire (#10) to feed your radiator fan via a 30 amp relay direct from the battery terminal on the starter solenoid. Even with a 6 volt alternator the system was never designed for these type of loads all on at the same time. Make sure the alternator battery wire is at least # 8 gauge but depends on the amps rating of the alternator. Everything in a 6 volt system has to be correct and most are not up to scratch. Regards. Kevin.

07-10-2016, 12:48 PM	#1
mjdunn Senior Member Join Date: May 2013 Location: Dry Ridge, KY Posts: 107	Misses out when the cooling fan is on My 1939 Ford runs perfectly until I turn on the headlights or the electric cooling fan on the radiator, and then it starts missing out. I have running lights that also come on at the same time the headlights come on. It is still 6 volt and I have a 6 volt alternator and an Otima Red top battery. I assume this is caused by too much draw on the electrical system. Have any of you had a similar problem? If so, is there anything I can do to remedy this?

07-10-2016, 01:48 PM	#3
rich b Senior Member Join Date: May 2010 Location: Minnesota Posts: 1,825	Re: Misses out when the cooling fan is on If the alternator output checks out, I'd check out connections down the line for the voltage drop. If an existing system that was working, watch for corrosion, loose or overheated terminal crimps and connectors, etc. If this is a new set-up be sure wires are sized for a six volt system. Relays for the fan and lights can be used to "unload" the main wiring harness and switches if that is the source of the drop.

07-11-2016, 07:00 AM	#8
G.M. Senior Member Join Date: May 2010 Location: Florida and Penna. Posts: 4,471	Re: Misses out when the cooling fan is on Check the voltage to the coil when the engine is running, it should be about 4.0 volts. Turn your fan on and read the voltage and I'll bet it's 3.0 volts or lower. Look for a bad battery or ground connection. G.M. __________________ www.fordcollector.com

07-11-2016, 07:26 AM	#9
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Misses out when the cooling fan is on Also, what is the rated amp output of your alternator? Is it even designed for this much current draw?

07-11-2016, 08:02 AM	#10
Henry/Kokomo Senior Member Join Date: May 2010 Location: Kokomo, Indiana Posts: 1,731	Re: Misses out when the cooling fan is on Check how the car is wired. I think there's a good chance that rich b (post #3) is on to a solution I'd also be wary of putting too many amps through the ignition switch as well. __________________ Henry

07-11-2016, 09:29 AM	#11
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Misses out when the cooling fan is on There really should not be anything attached to the ignition switch other than the ignition coil and the dash instruments. Relay trigger wires might be ok, but that is about it.

07-11-2016, 03:39 PM	#12
scooder Senior Member Join Date: Jul 2010 Posts: 2,593	Re: Misses out when the cooling fan is on It sounds like a possible wiring issue, this is only based on RKS.PA stating he has the same stuff but without the miss. It could be your fan is a higher amp than his though. So check your voltage as above. Definitely agree with the relay with power direct from battery. Not trying to be cocky here, a mechanical fan uses no amps. Martin.

07-11-2016, 05:33 PM	#13
mjdunn Senior Member Join Date: May 2013 Location: Dry Ridge, KY Posts: 107	Re: Misses out when the cooling fan is on The only thing running through the ignition switch is the trigger switch for the fan and the lights. The fan and lights are running straight off the battery through a relay. They are separate relays. The alternator is putting out 7 volts. The wire going to the fan is a 10 gauge wire. The wire from the battery to the relay for the lights is also 10 gauge.