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Convertible Top Not Working - Bad Switch?

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My convertible top is not working. When I press the switch nothing happens. I am trying to determine if the switch is defective. I attach a diagram of the switch terminals with the appropriate wires attached.

When the switch has no wires attached, there is continuity as follows:

Without pressing the top up or top down button:
Between terminals 1 and 3
Between terminals 2 and 5

When pressing the top up button:
Between terminals 1 and 3

When pressing the top down button:
Between terminals 2 and 5.

Without pressing the top up or down button, there is +12 volts at terminals 1, 2, 3 and 5.

When the top up button is pressed however, contrary to logic, there is no longer +12 volts at terminal 1. Likewise, when the top down button is pressed, there is no longer +12 volts at terminal 2. How can there be continuity but not +12 volts in these two situations? These two illogical situations lead me to believe that there is something wrong with the switch.

The manual for this vehicle describes the operation of the power top as follows:

With the ignition in the On or Accessory position, the top relay and top switch have power available through their respective circuits. When the console switch for the power is toggled up, the up relay coil is energized pulling the Normally Open contact to the common, and power flows thru the up wire on the hydraulic pump. Similarly, when the top switch is toggled down, voltage is supplied to the down wire.


Your help is greatly appreciated.


John
 

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  • Top Switch.png
    Top Switch.png
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Either a connection is fused open or a PTC current limited is fused open. Trace the impedance from load back to source. How many ohms and volts across each switch when open . Do not test Ohms when closed as this puts on 12V. If there is any V drop in mV, then Ohm reading will be wrong when connected to power.

If the current is limited by a common PTC that is high resistance i.e. >> coil resistance than the coil voltage drops to ground.
 
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Tony,
Thanks so much for your response. Your knowledge of electricity and electrical terms is much more advance than mine. Give me a couple days and I will get back to you,

John
 
Yes Engineering made me very geek like at an early age. Now after 40 yrs of bleeding edge and a few years of fixing my Dad's MGB for myself.... taught me about Lucas 3 way switches.

On-OFF-MAYBE
 
Hi all, When measuring voltage where are you picking up ground from? Without seeing a schematic or wiring diagram it is difficult to say for sure. I don't see a need for ground at the switch unless it is there for illumination. You might have excessive voltage drop at the switch contacts such that when current is flowing there is a voltage drop at the contacts not allowing full voltage to the hydraulic pump. One other thought is many convertible vehicles use a secondary safety circuit that would not allow the top to operated while the vehicle is rolling such as a signal from a park neutral switch or handbrake. Based on the ohm readings you gave terminals 1 and 3 are connected in top up position and 2 and 5 in the top down. If you measure voltage across 1 and 3 or across 2 and 5 with the switch engaged, good contacts would show around 500 millivolts or so. Anything more indicates a voltage drop across the contacts and a faulty switch.
 
Thanks so much for your rfranzk.

I found the wiring diagram for the top switch. I may have the wiring for the switch wrong. Please tell me if I am reading the diagram correctly. First, no ground wire (as you suspected) goes to the switch. Secondly, +12 volts (brown wire) goes to terminals 2 and 5 on the switch. The top down wire(yellow wire) goes to terminal 3. The top up wire (orange wire) goes to terminal 4. Now here is the problem. From the diagram, it appears that jumper wires go from terminals 3 to 1 and 4 to 6, but the original oem switch only has 5 terminals. Here is the other problem. The way I described the wiring of the switch in my initial posting is the way I found it. Now I did have some work done to the car and the mechanic could have changed things from the factory, but why would he add a ground wire to a top switch. I don't know only to say this mechanic had an ax to grind and maybe was sabotaging my top. The diagram that I have attached is comes from the manual for this vehicle. Its odd that the switch drawn in the diagram has the wrong number of terminals. What do you suggest? Forget the ground wire and the jumper wires?

Perhaps I mispoke in my initial posting. In the places I said there was +12 volts, that may be an inaccurate statement since I was only using a test light and NOT a multimeter. I will test again today using a multimeter and get back with the amount of voltage before and after the switch is pressed.
 

Attachments

  • Top Switch Diagram.pdf
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Hi John,
A wiring diagram helps a lot. This looks pretty simple. Apparently the hydraulic pump has 2 different windings for direction and you get power to the orange wire for one direction and yellow for the other. Looks like only 4 terminals on the switch are used so you are probably ok if your switch is original. Terminals 2 and 5 receive power (brown wire) from what appears to be an accessory relay that is energized only with ignition on. Terminals 2 and 3 are connected energizing the up relay and powering the yellow wire to the pump in the up position. Terminals 4 and 5 are connected energizing the down relay and sending power to the orange wire on the pump.

Check for power at the yellow and orange wires at the pump with the switch in its respective positions. If no power there then check at the switch. If there is power at the pump then check the ground for the pump motor. Grounds are a very common issue in automotive electrical problems. Worse case just jumper the switch brown wire to orange or yellow and see what you get.

A test light is usually sufficient for older automotive troubleshooting but they are a no no with computer controls unless they are high impedance self powered test light.

Thanks.

rfranzk.
 
Measure the resistance on Orange and yellow wrt frame ground when OFF. It should be in milliohms
Then measure voltage when ON. wrt. frame ground.
 
To All:

Thank you for you help. Rather than try to figure out what is wrong with the existing setup. I created my own setup very similar to the existing setup. My setup is working but it is blowing 40 amp fuses. I have started a new thread. Please , please look at this thread and give me you thoughts as to why the new setup is blowing fuses.

Thanks.
John
 
It sounds like an under-rated switch was used and may be blown. If a circuit is provided, better results can be achieved.
 
I found out why the fuses were blowing. I had too much hydraulic fluid in the motor. This was causing the motor overcompensate and use more amps due to the incorrect amount of fluid in the reservoir. Thank God I have the circuit fused. Otherwise I would have burned out the motor. As I reduced the amount of fluid little by little the circuit went from blowing 50 amp fuses to blowing 40 amp fuses to blowing 30 amp fuses to not blowing a 30 amp fuse. That is how I knew that fluid overfill was the problem. As I reduced the amount of fluid, the size of the fuse the circuit was blowing keep going down, and then the circuit finally stopped blowing fuses. The top works great now. Thanks again to everyone for your help. It is still a mystery why the original wiring would not work.
 
If I remember correctly there was a mention that this system was made by Lucas, the prince of darkness.
 
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