Technical Punto cabrio. Any auto electrician out there?

[FiorinoDan]

I am normally not too bad with electrics, but I think I need some superior advice.
On the hatchback, the handbrake switch earths directly to the handbrake warning lamp.
However, on the cabrio, the electric hood uses the handbrake switch as a safety device and earths to one of the relays in the boot.
I have got the Fiat manual but I cannot find how the relay links to the handbrake warning lamp.
To make things worse , the factory alarm has been replaced by a Clifford system, which I haven't got a clue how it is wired or operates!
Now here's my issue. The roof worked a couple of years, when I last used it. But now, nothing, nada, niente. The handbrake warning lamp does not illuminate when I put the handbrake on, but it lights if I press the fluid switch on the brake cylinder.
I have tested the handbrake switch with a multi-meter, and it appears to work properly, creating a circuit when released.
Would I be right in thinking that maybe the relays have degraded over time, or should I be looking for something more basic?
The only fuse I can find is the 40A one under the bonnet, and that is fine.
There is, what appears to be an earth wire, spare under the bonnet, which I may have dislodged when I have been charging the battery, but I have tried earthing it and it makes no difference. It is on a small loom near the battery, but the other wires are cut, so it may be part of the factory alarm system. HELP?..................:bang:

 

[Noddy]

From memory on my cabriolet it has two connectors on the handbrake switch. One for the dash and the other to the roof circuit. This kept the two systems separate as they were live feeds that earthed through the switch rather than getting a feed from the switch.

 

[FiorinoDan]

This is not the case on post 96 cabby's. There are two wires on the switch, but one is an earth and the other goes to earth one of the relays. I presume that the handbrake on light is fed from further down the line, but the wiring diagrams are a bit vague on this.
As my handbrake warning lamp doesn't light up, I suspect that there is a supply issue.
There doesn't appear to be power at the roof switch either, so I think one of the safety devices is (i.e. handbrake) is causing the problem. I need to check whether there is an earth at the relay, but it is difficult in a cramped dark lockup.

 

[FiorinoDan]

The handbrake switch is No40 in the diagram

 

[AndyRKett]

Assuming everything used to work, and you’ve not changed anything, either a connection or a wire has broken so check the connections at all the various places they join switches or relays. Then there is the possibility of a broken wire, finally a failed component. Generally it’s best to check the components work so if you just need to short something to ground via the handbrake for the roof to work then bypass the switch and short the roof ECU to ground or live or whatever it needs, if that works then change the relay, if that doesn’t work then look at connections or wiring.

People get hung up on wiring looms and the various components working but on these older cars you can usually take things out of the circuit and see if they work independently bypassing the switches and relays.

You could even short and bypass the relay if without touching the wiring to the handbrake switch, would give you some idea what’s going on

 

[FiorinoDan]

Assuming everything used to work, and you’ve not changed anything, either a connection or a wire has broken so check the connections at all the various places they join switches or relays. Then there is the possibility of a broken wire, finally a failed component. Generally it’s best to check the components work so if you just need to short something to ground via the handbrake for the roof to work then bypass the switch and short the roof ECU to ground or live or whatever it needs, if that works then change the relay, if that doesn’t work then look at connections or wiring.

People get hung up on wiring looms and the various components working but on these older cars you can usually take things out of the circuit and see if they work independently bypassing the switches and relays.

You could even short and bypass the relay if without touching the wiring to the handbrake switch, would give you some idea what’s going on

Thanks for the helpful information. I have bought new relays and diodes so I can replace them one at a time. But, as you have said, it will probably come down to a dodgy connection.
It is just a nightmare trying to follow the circuit, but I will give it my all!?

 

[Flyingsquirrel]

Thanks for the helpful information. I have bought new relays and diodes so I can replace them one at a time. But, as you have said, it will probably come down to a dodgy connection.
It is just a nightmare trying to follow the circuit, but I will give it my all!?

Did you get to the bottom of this?
Currently sorting out an electrical issue with our ‘98 cabriolet’s roof opening circuit and would really like a circuit diagram of roof electrics to see how they intended it to be.

 

[FiorinoDan]

Did you get to the bottom of this?
Currently sorting out an electrical issue with our ‘98 cabriolet’s roof opening circuit and would really like a circuit diagram of roof electrics to see how they intended it to be.

Did I get to the bottom of this? Sort of, but not in a way that will be helpful to you! I still think it was something very minor like a loose wire, but, due to lack of access, I never got round to checking it out.
In the end, I bought another Punto and sold my old one which, incidentally, was a 98.
How long have you owned yours?