Jump to content
Sign in to follow this  
truckin88

parking brake light stays on 312-8

Recommended Posts

truckin88

On my 312-8 it has the red LED indicator lights the parking brake one functions fine when the tractor is on and running, lights up and shuts off with the engagment and disengagment of the parking brake. But when I shut off the tractor and pull the key, the parking brake light stays lit no matter if the parking brake is engaged or not. All other electrical seems fine, hour meter only is on when the key is on, other lights work correctly. Any ideas?

Share this post


Link to post
Share on other sites
 
tractordave3128

the only thing i could think is wrong wireing

Share this post


Link to post
Share on other sites
 
nylyon

I haven't heard of that one before but I would suspect that the little light board is defective. When you hit the test switch and key is off do things light up?

Share this post


Link to post
Share on other sites
 
truckin88

I haven't heard of that one before but I would suspect that the little light board is defective. When you hit the test switch and key is off do things light up?

key is off, all lights light up when you hit the test switch....the parking one stays on when u let go of the test switch

Share this post


Link to post
Share on other sites
 
bitten

Put a flasher on it and people will think it is the security alarm :scratchead:

Share this post


Link to post
Share on other sites
 
Save Old Iron

The dash pod for these lights contain a certain degree of "logic" circuitry with the wiring. It is a kind of "if this wire is at 12 volts and the other wire is at ground then lite this indicator" type of response. If these circuits operate at 12 volts and ground, they do not like a voltage they cannot interpret - like 7 volts instead of 12 volts.

They cannot decide if the signal is low or high and fail to give you the response you expect.

There is (should be) a white wire coming from the parking brake safety switch up into the logic board for the indicator pad. With the ignition on, measure the voltage at the white lead to parking brake switch. In one position, there should be battery voltage on the white wire and when the parking brake position is changed, the 12 volts should change to a much lower voltage - probably less than 1 volt.

The point is you should see a big change of the voltage at the white wire on the parking brake switch when the parking brake position is changed from on to off. And one of the two voltages should be battery voltage !! If not, suspect the safety switch or wiring / connectors at the safety switch.

Don't know if the parking brake switch is adjustable in your model but make sure as you move the parking brake that the switch actually mechanically switches on and off - the switch could be loose (or broken) and the parking brake never engages / disengages the switch. Check that visually or with a multimeter on the ohms setting.

Check the ground wire going into the dash pod harness - make sure its a good ground. Bad grounds drive "computer logic" into doing wacky things. I don't really suspect this area as your test switch function works ok. But who knows.

good luck - keep us updated.

:scratchead:

Share this post


Link to post
Share on other sites
 
jpmcleod

Truckin88,

I am picking up a 312-8 tomorrow and I hope it works out good for me. I will have to get used to the black hood and rear fenders compared to my other older two Wheel Horses but the "price is right". The only thing it needs as I can tell is a new muffler. It is all complete, runs good and the mower deck works fine. It has some rust on the hood and missing a headlight lense but the rest looks good. I may be gettinmg back with you at a later date if I run into any problems. I hope to start tearing it apart and repaint it when the weather cools down.

Share this post


Link to post
Share on other sites
 
marvairplanes

Black hood on a 312-8 ?????

Are you sure ????

Marv (NW OH)

Share this post


Link to post
Share on other sites
 
Duff

Black hood on a 312-8 ?????

Are you sure ????

Marv (NW OH)

Marv, I'll bet he's talking about the black grille area compared to his all red older machines. JMHO..... :scratchead:

Duff

Share this post


Link to post
Share on other sites
 
jpmcleod

It's only black in the grille area.

Share this post


Link to post
Share on other sites
 
truckin88

The dash pod for these lights contain a certain degree of "logic" circuitry with the wiring. It is a kind of "if this wire is at 12 volts and the other wire is at ground then lite this indicator" type of response. If these circuits operate at 12 volts and ground, they do not like a voltage they cannot interpret - like 7 volts instead of 12 volts.

They cannot decide if the signal is low or high and fail to give you the response you expect.

There is (should be) a white wire coming from the parking brake safety switch up into the logic board for the indicator pad. With the ignition on, measure the voltage at the white lead to parking brake switch. In one position, there should be battery voltage on the white wire and when the parking brake position is changed, the 12 volts should change to a much lower voltage - probably less than 1 volt.

The point is you should see a big change of the voltage at the white wire on the parking brake switch when the parking brake position is changed from on to off. And one of the two voltages should be battery voltage !! If not, suspect the safety switch or wiring / connectors at the safety switch.

Don't know if the parking brake switch is adjustable in your model but make sure as you move the parking brake that the switch actually mechanically switches on and off - the switch could be loose (or broken) and the parking brake never engages / disengages the switch. Check that visually or with a multimeter on the ohms setting.

Check the ground wire going into the dash pod harness - make sure its a good ground. Bad grounds drive "computer logic" into doing wacky things. I don't really suspect this area as your test switch function works ok. But who knows.

good luck - keep us updated.

:scratchead:

I understand this, but shouldn't these things be on a switch power....I guess not because of the test light. I am just wondering as it functions as it should when the machine is running, and then stays on when off. I really like this tractor it works awesome and is in good shape.

Share this post


Link to post
Share on other sites
 
Save Old Iron

If all the inputs are confirmed good to the indicator pod - confirmed good both with ignition off and on - then no where to go but a fault in the way the dash pod circuitry is processing the signal.

Share this post


Link to post
Share on other sites
 
Save Old Iron

as far as the switched power issue, here is where the pod could be live at all times

312-8parklite2.jpg

I say could because I am not sure if the connection at #11 at the pod is just a pass thru for the battery voltage to the test switch or if the battery voltage on pin 11 is introduced into the pod circuitry at this connection. If the pod actually picks it's power at pin 11, then it's live at all times. The fact that the parking indicator lites with the key off means power is coming from SOMEWHERE to the module.

Same concern with pins 1 and 12 for ground . Pin 1 may be just a pass thru

:scratchead: but the pod could be picking up grounds for 2 electrically separate circuits within the pod - one being ground at pin 1 , the other circuit grounded thru pin 12.

One of these ground pins could be corroded and screwing with just the parking lite logic.

Share this post


Link to post
Share on other sites
 
truckin88

I believe they were punch down connectors as well (as seen in network and telecom wiring) , maybe I will repunch and see whats up with the voltmeter. It is possible that a piece of wire is bare and completing the circuit somewhere, esp after 21 years

Share this post


Link to post
Share on other sites
 
truckin88

I forgot my punch down, will bring it tomorrow for the molex connector, but I know the pb switch is working fine, cause I tested it's function and the wires going to it. I did reseat the wires in the molex with a small flat head, and now the engine oil light will not light up when hitting the test switch. I will bring a punch down tomorrow from a friends and repunch everything.

The PB light is still staying lit when off, it is like something is jumping the switch and going to a constant. , but grounding out when on???????????

Share this post


Link to post
Share on other sites
 
Save Old Iron

My favorite saying when I was in the field fixin' stuff was

"When you hear hoof beats - Think HORSES not ZEBRA's"

Always try for the common, obvious issues first. Don't go too exotic too quickly.

The Horses here would be the dash pod electronics or corrosion at the grounds or punchdowns.

If you want to hear my thoughts on ZEBRA stuff, read on .....

The Demystification guide makes a claim that the switch positions shown on the diagram " are drawn in the position necessary to make the circuit function". I'm guessing here that means to turn on the parking brake light, the parking brake switch must be applying the 12 volts from the hour meter connection / orange wire thru the PB switch to the module. So far so good.

It appears pin #8 on the punchdown receives 12 volts to turn on the light. Break that connection and the lite should go out.

I'm also guessing that the dash indicators are LED's and not incandescent bulbs - correct me if I'm wrong here.

LED's only require 0.020 to 0.030 amps to lite up - some at a voltage as low as 1.5 to 2 volts. If these are more than just hardwired LED's and are driven by transistorized devices, voltages as low as 0.7 volts and micro amp currents could turn on the LED indicators. Small leakage currents or even slightly conductive "buildup" in or near the connections of the punchdown block could cause issues. Not knowing what is in the pod makes it hard to say.

Can the pod be disconnected from the punchdown connector and that junction checked for buildup or liquid forced into that area - possibly from a recent pressure washing ??

I know you said the PB lite works OK when the tractor is running - just wanted to say that I clearly understand that. But you might want to try this just out of curiosity.

I'm not sure if the PB switch is hardwired or has push on connectors - when the tractor is off and the PB lite is on - remove the white wire from the PB switch and see if the PB lite goes out. There could also be a slightly conductive pathway thru the PB switch that does not allow the voltage at punchdown #8 to drop off far enough to shut of the PB lite. Let's find out !

Who knows - you may replace the dash pod and we will all see a herd of horses run by and problem will be fixed. But it's the occasional Zebra herd that makes me get involved with the tough and weird and interesting issues. Soon we will find out.

Thanks for the continuing updates.

Share this post


Link to post
Share on other sites
 
kpinnc

I'm also guessing that the dash indicators are LED's and not incandescent bulbs - correct me if I'm wrong here.

LED's only require 0.020 to 0.030 amps to lite up - some at a voltage as low as 1.5 to 2 volts. If these are more than just hardwired LED's and are driven by transistorized devices, voltages as low as 0.7 volts and micro amp currents could turn on the LED indicators. Small leakage currents or even slightly conductive "buildup" in or near the connections of the punchdown block could cause issues. Not knowing what is in the pod makes it hard to say.

Can the pod be disconnected from the punchdown connector and that junction checked for buildup or liquid forced into that area - possibly from a recent pressure washing ??

Chuck makes a good point.

There are two small bolts and one 9-pin connector on the PC board. It is very easy to remove. Just use caution when taking it off, as the LED leads are easy to break when they are pulled from the rubber grommets that hold the red lenses on.

The board itself sometimes has a thin "gel" coat on the component side, and sometimes it does not. Regardless, it would be a good idea to remove the board, and clean it with an electronics-safe cleaner. Often times dirt and other contaminates build up under the dash, which can hold moisture and breed a bit of corrosion. It would also be a good idea to pull back the foam cover on the underside of the board and clear away any contaminates as well.

The PC board itself is very simple. Only 1 small IC chip, 2-3 transistors, and the rest is diodes and glass resistors. Just look for any corrosion when it's clean- and it may not be a bad idea to seal it after it's completely dry.

Good luck!

Kevin

Share this post


Link to post
Share on other sites
 
truckin88

guys, at the switch it is a plastic harness which has 2 female push on connectors, I tested witha simple test light, when the ignition is on the orange has voltage when it is not on, the test light does not illuminate. The white has no voltage and is dead to the test light. Until the switch is closes the circuit. I will repunch when home.

Since the switch seems to check out. I think the issue is at the board or the pd block.I am also thinking that something on the board is conductive and giving power to this light from a constant.

Share this post


Link to post
Share on other sites
 
Save Old Iron

I'm not sure if the PB switch is hardwired or has push on connectors - when the tractor is off and the PB lite is on - remove the white wire from the PB switch and see if the PB lite goes out. There could also be a slightly conductive pathway thru the PB switch that does not allow the voltage at punchdown #8 to drop off far enough to shut of the PB lite. Let's find out !

If you have not started to tear apart the pod, it may still be of some value to check the PB switch by actually disconnecting the white wire from the PB switch to the pod - this will POSITIVELY ABSOLUTELY confirm the PB switch does not have leakage current thru it - the current it takes to lite the incandescent tester is about 100 times the voltage and current needed to turn on an LED in the pod.

THOSE WHO DON"T LIKE ZEBRA STUFF STOP READING HERE !!

A good comparison of this idea is how a relay on the starter uses very little to current to engage the relay but CONTROLS a much bigger current at it terminals.

So we end up putting 1 - 2 amps of current thru the relay coil to engage contacts that control 50 amps or more of starter current.

So the relay could be termed a device that has a 50 times CURRENT GAIN ( 1 amp controls 50 amps)

A transistor circuit usually has at least a 20 x current gain and the gain can be as high as 2000X , Actually, depending on circuit configuration, the transistor can be used to control current or voltage gains.

So my point is that a voltage / current level that will not lite an incandesent bulb will EASILY lite a transistorized LED circuit.

Just today's Zebra lesson.

Share this post


Link to post
Share on other sites
 
truckin88

If you have not started to tear apart the pod, it may still be of some value to check the PB switch by actually disconnecting the white wire from the PB switch to the pod - this will POSITIVELY ABSOLUTELY confirm the PB switch does not have leakage current thru it - the current it takes to lite the incandescent tester is about 100 times the voltage and current needed to turn on an LED in the pod.

THOSE WHO DON"T LIKE ZEBRA STUFF STOP READING HERE !!

A good comparison of this idea is how a relay on the starter uses very little to current to engage the relay but CONTROLS a much bigger current at it terminals.

So we end up putting 1 - 2 amps of current thru the relay coil to engage contacts that control 50 amps or more of starter current.

So the relay could be termed a device that has a 50 times CURRENT GAIN ( 1 amp controls 50 amps)

A transistor circuit usually has at least a 20 x current gain and the gain can be as high as 2000X , Actually, depending on circuit configuration, the transistor can be used to control current or voltage gains.

So my point is that a voltage / current level that will not lite an incandesent bulb will EASILY lite a transistorized LED circuit.

Just today's Zebra lesson.

understood, but the white wire on that switch is fed by a ign on power (switched power). which via volt meter is doing it's job. I am thinking it could be on the pod,

Share this post


Link to post
Share on other sites
 
Save Old Iron

and all said and done - remove the PB LED from the pod and wire in a direct connection to another LED. You could install another LED in the pod area behind the PB display. Power the LED directly from the white wire - insert a current limit resistor ( probably around 470 ohms from radio shack) in series with the LED and ground the resistor to the dash pod area.

You will have a direct wired - dedicated LED directly off the PB switch - this can't help but work correctly - not original but will bring the tractor indicators back to full - normal - function.

Share this post


Link to post
Share on other sites
 
truckin88

guys,

I took it apart with a volt meter handy. I removed the board and foam, cleaned it, then covered it with some of the foam and electrical tape. I test the Molex connector with the board off. I tested the top and the inside of it, at the connections. It only gets power at the red constant when the tractor is off, not even the pb signal wire. Yet when the board is plugged in it lights the pb light. I swapped around the bulbs, and only the pb light would light. Bad board?

Share this post


Link to post
Share on other sites
 
nylyon

I think that's really what you're left with. You may want to post in the wanted section to see if anyone has an extra?

Share this post


Link to post
Share on other sites
 
hummod

My first thought would be a problem on the board with the IC chip. It could be a

bad transistor that drives that bulb too. I had a similar problem but it was the oil light and not the parking brake light that was staying on. I did have a second board from another tractor that I swapped to verify that it was a bad board. My

job is working with electronics so I have good access to parts and equipment.

I will move this reply back out of the wanted section to your original thread.

Larry (hummod)

Share this post


Link to post
Share on other sites
 
truckin88

it was the transistor on the circuit. a $1.00 fix. The reverse engineering of this board can be found ain the FAQ section

Share this post


Link to post
Share on other sites
 

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...