Engine Quits when Instrument Light Turned On

johndduvall

johndduvall

Member
I acquired "Tinker" about a month ago. I've been sorting things since that time. It came with a 12v negative ground system. While test driving the other day, I twisted the instrument light on and the engine began to quit. Turned it off, the light went off and engine came back.

Before I take the instrument panel off, any ideas what would cause this to happen?

Thanks!

John D.
 
Not sure since we don't know about potential wiring troubles lurking somewhere, but makes me think the dash light wire is connected to the same terminal as the ignition switch wire, causing a temporary loss of power when it is switched on. Maybe move the wire for the dash light to the opposite side of the Ammeter to see if that helps. The electrical experts here on the Barn will have the answer.
 
I experienced a similar problem with a 1931 Coupe I restored for a friend. The car had previously been "restored" by a "professional", but my friend said he could never be sure he'd make it home after a drive. It didn't run right on the road, he said. After rebuilding the entire car - including the ignition system - a test drive showed that sure enough - the engine missed upon acceleration or at a sustained speed. I checked out everything and found nothing wrong. Backtracking, I decided to disconnect electrical items until I had isolated the troublemaker. By sheer dumb luck, the first item I disconnected was the oil pressure gauge light wire that ran to the terminal box or ammeter, I don't recall which. (An auxiliary gauge was mounted at the bottom of the instrument panel.) A test drive proved that the light in the oil pressure gauge was causing the engine to misfire under power demands.
So, I can see why turning on something as equally harmless as a defective instrument light could play havoc with the ignition system. Try completely disconnecting the wire first and see if that makes a difference. If it does, then do as "mcgarrett" suggests and connect it to the ammeter terminal closer to the speedometer, the usual place for this wire (on a 6 volt system). If the ignition cuts out again, then you know for sure there is a short inside the instrument light, probably a frayed wired where it exits the light's body.
Marshall
 
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Marshall V. Daut said:
I experienced a similar problem with a 1931 Coupe I restored for a friend. The car had previously been "restored" by a "professional", but my friend said he could never be sure he'd make it home after a drive. It didn't run right on the road, he said. After rebuilding the entire car - including the ignition system - a test drive showed that sure enough - the engine missed upon acceleration or at a sustained speed. I checked out everything and found nothing wrong. Backtracking, I decided to disconnect electrical items until I had isolated the troublemaker. By sheer dumb luck, the first item I disconnected was the oil pressure gauge light wire that ran to the terminal box or ammeter, I don't recall which. (An auxiliary gauge was mounted at the bottom of the instrument panel.) A test drive proved that the light in the oil pressure gauge was causing the engine to misfire under power demands.
So, I can see why turning on something as equally harmless as a defective instrument light could play havoc with the ignition system. Try completely disconnecting the wire first and see if that makes a difference. If it does, then do as "mcgarrett" suggests and connect it to the ammeter terminal closer to the speedometer, the usual place for this wire (on a 6 volt system). If the ignition cuts out again, then you know for sure there is a short inside the instrument light, probably a frayed wired where it exits the light's body.
Marshall
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Marshall, if a short was occurring in the light, would it still burn bright or not at all? Also, if left in that position, wouldn't the 40A body fuse blow?

Thanks for your reply.

John D.
 
mcgarrett said:
Not sure since we don't know about potential wiring troubles lurking somewhere, but makes me think the dash light wire is connected to the same terminal as the ignition switch wire, causing a temporary loss of power when it is switched on. Maybe move the wire for the dash light to the opposite side of the Ammeter to see if that helps. The electrical experts here on the Barn will have the answer.
Click to expand...

Thanks for the info.

John D.
 
POSTED 02-01 2023 01:58 PM:

I will say that the wire is most likely not hooked to the ampmeter but might be hooked to one side of the ignition switch!
 
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"Marshall, if a short was occurring in the light, would it still burn bright or not at all? Also, if left in that position, wouldn't the 40A body fuse blow?"

Apparently, the light bulb in the oil pressure gauge did not blow out or the owner would have mentioned that. And I don't recall the bulb burning out when I first test drove it after rebuilding the entire car. Or maybe because the bulb was so dim to start with that we didn't notice it being burned out? That's an interesting question because I know the owner never drove the car at night - he couldn't trust it to make it back home and the previous "restorer" had not made all lights functional. So, possibly the present owner at the time never knew that the bulb had burned out. We replaced all bulbs during the rebuilding process and I test drove the car during the day. So, I most likely wouldn't have noticed if the bulb had blown out. It was not connected to a fuse.
It was very frustrating trying to find the source of that misfire after so much had been done to the car. What a relief it was to discover the problem was the light in the oil pressure gauge. I simply disconnected the wire so that the engine would run properly. Not a fix, but that did solve the misfiring problem. :)
Marshall
 
Marshall V. Daut said:
"Marshall, if a short was occurring in the light, would it still burn bright or not at all? Also, if left in that position, wouldn't the 40A body fuse blow?"

Apparently, the light bulb in the oil pressure gauge did not blow out or the owner would have mentioned that. And I don't recall the bulb burning out when I first test drove it after rebuilding the entire car. Or maybe because the bulb was so dim to start with that we didn't notice it being burned out? That's an interesting question because I know the owner never drove the car at night - he couldn't trust it to make it back home and the previous "restorer" had not made all lights functional. So, possibly the present owner at the time never knew that the bulb had burned out. We replaced all bulbs during the rebuilding process and I test drove the car during the day. So, I most likely wouldn't have noticed if the bulb had blown out. It was not connected to a fuse.
It was very frustrating trying to find the source of that misfire after so much had been done to the car. What a relief it was to discover the problem was the light in the oil pressure gauge. I simply disconnected the wire so that the engine would run properly. Not a fix, but that did solve the misfiring problem. :)
Marshall
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Marshall,

I was referring to my car with that question. I just went out and turned my key on and then the instrument (twist) light. The body fuse didn't blow and the amp meter indicated a slight discharge.

Thanks,

John D.
 
Most electrical problems are caused by bad connections. Take the terminals off the junction box and clean them up by scraping or sanding. Use an electrical grease when you re assembly them. Do one side at a time. Do the same with the connections on the coil and at the distributor and everywhere else that has connection points. Use a volt meter to measure the voltage at the different connection points before you take them apart which may help eliminate some work.

It could also be a bad ammeter. The voltmeter will tell you if that is the case or you can just bypass the ammeter with a short jumper wire. The connectors on the back of the ammeter need to be cleaned up too.
 
Does the car in question have an original type Electro Lock ignition switch or a modern type switch? This has an affect on how it's all connected up.
 
johndduvall said:
It has the A-11575-EMA RE-POP ignition switch.

Thanks,

John D.
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Is it a hot switch powering the coil up from the battery or is it a ground cutoff switch from coil to distributor?

If hot, where does the switch get it's power, ie from the generator circuit through or prior to the amp meter or direct from the battery side?

What is the panel light connected to in order to get power?

All these questions are relevant if there is a switch problem or if there is connection problem. The original ignition switch only controlled the ground from the coil to the breaker points in the distributor. The coil was powered from the battery terminal in the terminal box. There could also be a problem with polarity at the coil connections. The + side generally connects to the distributor breaker points and the - side connects to the battery. A polarity tester will confirm a correct connection in any case. The November 1929 service bulletin confused the polarity question by the way the illustration shows it to be connected. According to that figure, Ford switched polarity on the coil with no mention of a coil change. Their intent was to change the coil power over to the generator side so that is would register a discharge when the coil was powered up. This made it a valuable tool to check the ignition function.

I've had the dash light short out on me before and it burnt the dash light wire. In this case the wire acted as the fuse which could have started a fire. It was connected to the amp meter for power and it shorted to the speedometer housing. Be very careful how you connect the dash light in any case.
 
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Interesting thread.

I've always been a fan, personally, of bone stock Model A's. 6V POS ground, original gennie, no add on oil pressure gauges and such hanging off of the bottom of the dash. I WILL surrender to a non-popout ignition switch.

The older I get the more I realize Henry Ford was a little smarter than what we are:p Upgrades and re-engineering often lead to Model A Miseries.
 
Jeff/Illinois said:
Interesting thread.

I've always been a fan, personally, of bone stock Model A's. 6V POS ground, original gennie, no add on oil pressure gauges and such hanging off of the bottom of the dash. I WILL surrender to a non-popout ignition switch.

The older I get the more I realize Henry Ford was a little smarter than what we are:p Upgrades and re-engineering often lead to Model A Miseries.
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I am indeed in agreement with you. My entire collection remains stock. Wayne
 
I had this same problem except it happened when I turned on the electric wiper. When I installed the wiring for the wiper, I wired it to the ignition switch so that when I turned off the key the power to the wiper was also off. Everything worked fine as long as the motor wasn't running but when it was, and I turned on the wiper motor on the engine would die. I'm glad that I found this in my shop and not on the road while it was raining. I moved the hot wire from the ignition switch to the voltage gauge and now it works fine and does't kill the motor when I turn on the wiper.
 
Grumps said:
I had this same problem except it happened when I turned on the electric wiper. When I installed the wiring for the wiper, I wired it to the ignition switch so that when I turned off the key the power to the wiper was also off. Everything worked fine as long as the motor wasn't running but when it was, and I turned on the wiper motor on the engine would die. I'm glad that I found this in my shop and not on the road while it was raining. I moved the hot wire from the ignition switch to the voltage gauge and now it works fine and does't kill the motor when I turn on the wiper.
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Grumps, this is a great learning thread for me, and your post causes me to want to dig deeper into the knowledge base present here.

Would the cause of Grumps issue be: by wiring the wipers to the 'switch on' side of the ignition switch, he has created a parallel circuit in series with the primary ignition circuit, and the voltage and current to each load will be reduced proportionate to the amount each load draws??

Adding the wiper motor will rob a good deal of the current needed to saturate the primary side of the ignition coil. If there is secondary spark at all, I'd expect it to be a miserable, dribble of a spark.
 
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The coil should be connected to the generator terminal in the terminal box per the service bulletin. The key switch should control the ground path between the distributor and.the coil. An electric wiper should be connected to the generator side of the terminal box so it will register on the amp meter. It should have its own switch but modern replacements don't have an internal switch so an under dash switch would be needed. The dash light connection to the amp meter wasn't one of Fords better ideas but it was all they could do to make it work reliably.

The problem with adding circuits to the terminal box is the limited space in there. It's crowded with just the stock wiring. A person can add a circuit to the battery at the starter switch but it won't register on the amp meter. It should be fused near to the power source wherever it is connected.

If any electric component has a wire come loose or isn't functioning correctly causing high resistance, it can really tax the other systems. A person should be sure to secure wiring connections as well as possible for besr reliability.
 
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