The Stovebolt Site Forums The Shop Area The Electrical Bay Heater keeps ignition on

Hi all,
I have a question about my 61 c10. When I shut off my truck with the heater on high, it keeps running for a while (10-20 sec.) before stopping. With the heater off, works fine. Even at medium or low it keeps running just for shorter period. All other electrical is fine.

Where should I start?

Thanks

WHAT THE FU-HELL? Gotta be in the wiring somewhere, somehow. Or maybe it's the ignition switch. I'd say start by looking under the dash for any suspicious looking wiring- burnt, add-on, etc. Then I would test the ignition switch with a volt-meter. Good luck.

Joe Parrie,

What an interesting post. I wonder if the heater came stock with the truck or was added by the dealer or a previous owner after delivery.

If you what you describe is true, there must be some connection between heater wiring and ignition wiring...as Oldcarandtrucknut pointed out.

What's interesting is that the run-on time is affected by the heater motor speed. The more voltage applied to the heater motor, the longer the engine runs.

This must mean the connection, whatever it is, in on the load side of the fan speed switch. Does this truck have a new alternator that may have been added recently?

Can you cause this run-on by switching the headlights or any other device on. Although the ignition switch is a common junction for both heater (ACC) and ignition, the fact the the run-on time changes with fan speed sort of precludes the switch from the list of causes....I think!

I have a picture of a fuse block, and the fuse for the heater is adjacent to a pair of pass through terminals for the igniton. Again, these are on the line, or supply side of the fan speed switch, so it still doesn't make sense this could be the culprit. Be sure to keep us posted and maybe someone will pop in with a real deal.

Stuart

When you shut the ignition off and the blower is still spinning, the blower then acts like a generator. So your getting voltage feed back to the ignition, to keep the engine running for a while. High speed the blower spins longer, low speed a shorter time, when shut off.
So, that's what's probably going on,I just don't know where you would look to fix it. (sorry) Maybe the ignition switch????

Hope this helps. When you turn or spin a d/c motor it will make voltage.

55, that kinda makes sense, but for 10- 20 seconds? If that's what it is, then it seems like the ignition switch isn't opening all circuits (shutting down).

Ok guys,

I just returned from the garage and here is some more info.

The ignition switch is new. The blower motor is new. As near as I can tell, the heater is a factory unit, the deluxe model with the 4 controls on the dash. The heater switch is also new.

If I disconnect the wire at the blower motor the engine dies right away when you shut of the key. The wiring under the dash looks just like a new truck, no frayed wires or butt connectors, etc. The control resistor in the airway is good.

The only thing that I can say is the replacement heater motor has a ground wire that is connected to the body of the heater housing. The original did not have this wire. By the way, I jumpped a wire from this ground directly to the battery negative and same result.

I also connected a test light to the positive side of the coil and you can clearly tell that the light stays on longer with the fan switch on as compared to off.

This really has me stumpped. The blower does run at a high speed, like I assume it should and maybe it is generating the extra.

Ya got me.

Whoops!

I forgot, the alternator is a standard delco with the battery wire on the back and the 2-wire connector on the side. Someone before me put it on and it works great. No battery run down problems if it sets or anything like that.

If it is a blower motor turned generator, I wonder if anyone else has had this happen?

Thanks

As a test,disconnect the heater motor at the heater,run a jumper wire from a switch controlled curcuit on the fuse block,to the heater motor,what does it do now?

Joe Parrie,

How or when did this problem crop up? Is there any cause and effect you can think of, like the new ignition switch or new heater motor.

I'm not a motor man, but I strongly doubt if that little fan motor could produce enough voltage to make the ignition run-on...but I have been wrong before.

Stuart

Ok,

I ran a wire to the only switched fuse in the fuse block which is the one that feeds the heater circuit. It has a spade terminal on the left of the fuse and a brown wire on the right that goes directly to the fan switch and no other place. The spade is on the feed side of the fuse. I pulled the fuse so the heater wiring is out of the circuit. The fan runs on high speed when the ignition switch is on and the engine still runs for a short while, just like before.

I am starting to believe the fan is running like a generator as earlier discussed, but I need to get a wiring diagram to see if the coil circuit is connected with the heater motor when the ignition switch is in the off position. That is the only way I can see it doing this.

If anyone has a diagram handy, I would appriciate knowing how this circuit is set up.

Thanks for all your help, this should turn out to be a learning experiance!

right now I can't think of anything else,Joe.I'm very interested is this keep us imformed please.


Boyd

Stuart,

I can't tie it to any particular change. I thought it was a bad connection in the ignition switch to start with, so I changed the switch. I noticed that sometimes it would shut off instantly, like normal and sometimes not, and it was by accident that I noticed that the fan switch would kill it. If I shut off the key, it would run for a few seconds, but if I shut off the key and then turn off the fan switch it dies instantly. At first I didn't believe it, but you can easily tell the difference.

Joe

The heater is probably wired into the ign. side of the switch. Wire the heater so it is in the acessory side.

I think Wrenchbender has it figured out.

Joe's last post leads me to believe the problem arose, he changed the ignition switch, and the problem is still there. This would mean it was wired into the ignition switch incorrectly before he changed it wouldn't it.

It will be interesting to see the outcome of this gremlin!

Stuart

Ok I have a question about which side of the ignition the fan is wired to. There is a brown wire that goes from the fan switch directly to the fuse marked heater in the fuse block. I have traced the entire wire from end to end and it has no splices to anything else. The ends are the factory plastic ones and the power at the fuse goes off when the ignition switch is shut off. If I pull the fuse, problem is gone. The ignition switch also has the factory plug with no changes to the wiring that I can see (the wrap over the wires looks factory). So does this mean that the connection to the coil is upstream from the fuse for the heater? I am going to try to find a wiring diagram, maybe that will help.

Thanks again everyone.
JOE

Joe as another test connect you jumper wire right to the heater motor,bypassing the heater switch,the other end to another curcuit,such as the radio,see if that changes anything I'm also wondering if a diode between the heater switch and the heater motor might fix this.I don't know what value however

Boyd

My truck doesn't have an alternator of course so I am going to guess at what I think the problem is. I understand that the alternator has a connection to the ignition switch, which supplies voltage to allow the alternator to build up it's field, when the motor is first started. When the iginition is turned off, it probably takes a while for the alternator voltage to collapse. Normally the engine would stop first. So I think maybe the alternator is supplying voltage through that wire and somehow through the heater connection.

I would be inclined to disconnect the alternator somehow, and see if the problem still exists.

Nothing unusual to have an engine cooling fan maintain the engine running after shutting down the truck. Earlier post described the fan turning from a motor to a generator when the ignition is shut down. As the fan looses speed the voltage generatored by the fan back into the system also dies down so in turn does the truck. Possibly to test that this is the case disconnect 12v to the heater fan and sustitute a test globe. Check operation again using the globe as a load instead of the heater fan. Having wired numerous hot rods this generation effect is not uncommon some do some don't. To overcome the problem I have used a diode from a wrecked alternator in series with the 12v to the engine fan. Solder some wires to the diode you may have to file the top of the diode before it will accept solder. Cover in heatshrink and mount safely. Heater should be wired to the accesories position on the ignition switch via a fuse to the heater also mentioned earlier but some installations do not have an acessories facilty. If the run-on effect is due to the heater motor the install of the diode will stop this . You will need to ascertain which direction the current flows thru the diode with a meter as it will only allow current flow one way. If you haven't got a meter just make some temporary connections by twisting the wires together. one way it will work one way it won't. I am suprised the a heater fan motor would do it but with electricity whether it be 12v 110v 240v or 22000kv nothing suprises me.

Fred,

That was one of my initial thoughts also. DA #2, when conveniently connected to the coil terminal for key switched power can back feed and cause run-on.

The symptoms seem to have just recently shown up, and appear to be controlled by heater fan speed....it's a puzzler for sure.

Pulling the DA plug could answer that question though.

Stuart

I must say that I am intrigued by problems like this. The fan motor thing is really interesting too.

I would try slipping the alternator belt off, then start it up and shut it down with the fan on. Does the engine shut off right away?

Wow! Thanks for all the responses! This is a great site. I have the next couple of days off so today I am going to go at it again. I will report back what I find out.

Thanks again for all your help everyone!

Joe

Ok guys, here it is.

I have installed a diode out of an old alternator in the line right at the heater blower motor. Fixed it. It would appear that the heater motor indeed was generating enough to keep the ignition energized for a few seconds after turning the ignition switch off.

In case anyone else has this crop up, I used a diode from a 70's vintage Motorcraft alternator. (Please don't tell anyone it was a Ford) The diodes in this alternator are soldered to a plate and I was easily able to solder a short wire onto the end that came off the plate. The heater blower is wired with 1/4" spades, so I just used some crimp-on automotive connectors to make the connection. It does have to be installed in the right direction. One way you have no current to the motor, the other way you have no current comming back to the ignition.

Thanks again for all your help with this, and have a very merry Christmas!

Joe

WOW, I sure learned something from this thread...who'd have thunk!!
A few members had this pegged from the beginning, congrats to you guys.

It's great you've solved the problem.

Stuart

Any of blower motor with permanent field magnets will generate 12 0r 6 volt depending on the voltage of the motor. The fan has enough momentum to spin it for a few seconds with enough amps and voltage to run the engine ben there done that.