I need some help. I have a 1990 XJS V12 Convertible and have been troubleshooting a problem with the convertible top not working. I have checked the handbrake mechanism, the switch, both relays and they are OK. Grounds and switches, etc. all seem to work OK.

What I need to know now is 1. Where is the neutral switch? So that I can check that. But I suspect that it is OK. and 2) How do I remove the ECM to test that. I see that it is almost impossible to pull the switch because try a metal bracket holding the ECM is in the way. When I try to remove that bracket and ECM / relays it looks like the fluid reservoir is coming out and I am concerned about breaking some line.

 

Mi Foodie,

As you probably know, there are "only" 3 conditions that need to be met for the ecu to allow the top to operate:

- Ignition In Pos II
- Handbrake on
- Car in Park or Neutral

The most common fault is naturally the handbrake switch. I would suggest just bridging the terminals to earth in order to bypass this.

The transmission selector switch is not usually an issue. It's on the side of the transmission so not very easy to access. I would check by trying the hood in Park AND Neutral. After that, if you don't have easy access under the car, check by backprobing the ecu (as below).

If you're then absolutely sure that the relays are ok, I would swap the switch wires over to a known working window switch. Remember that prising the switch out can damage the fragile surround. I would lift the skislope and do it from underneath.

If that all proves fruitless then the best way is to backprobe the connection block to the ecu to see that the conditions are being met and the switch is opening the circuit.

Good luck

Paul