Convertible Top ECM Removal

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.

Re your switch, it’s the same type as the handbrake switch you checked. And you’re right, at least the other-side of the circuit - the starter side - is working because the car wouldn’t start if the switch wasn’t closing to ground (at least on that 1/2 of the circuit). It may be that the Neutral swtich has ONE contact, not three as it looks like the Conv top wire and starter relay ground wire pass to the same contact.

Hopefully you’ll get some advice on how to remove the top ECM so you can check it’s wiring for sure before giving up on it.

~Paul K.

The ECM is beside the hydraulic pump.
You can get to it once you remove the relay bracket.
Is that your concern ?

If you search this topic it shows the relay bracket removed.
You have to go a long way down the topic to see the photos.

Convertible top cylinder ( ram )

I am guessing when you move the top operating switch on the centre console you do not even hear a relay click. From memory there is a multipin connector in the loom for the ECM.
If you have the wiring diagram you could pull it apart and check you have the two grounds you need and also the battery supply via the ignition switch.
You could defeat the neutral and handbrake switch by cutting into the wires just in front of the ECM and grounding them. Then you can operate the top anytime, and if you are sensible you will not do it at 60mph on the freeway.
If the ECM is fried and hard to replace you can bypass it and use Paul’s idea of simply controlling the top from switches on the console.

OK so removing the relay bracket does not move the hydraulic pump and ECM.

Thanks, I feel more comfortable now.

OK. I was able to remove the ECM and unplug the wires going to the motor. With the engine on, Handbrake engaged and the top switch jumped and both relays in place. I have no power to either blue wire that goes to the motor. I assume that means that the ECM does not work. Would that be a correct assumption? Also how to I test the motor?

Getting there

For reference the FBook thread on this is here:


Bill, as I recall, the motor whirred to life when you jumpered the relay sockets from pin 30 to 87 one at a time on both sockets (as long as the opposite socket was jumpered from 30 to 87a). That says the motor is ok.

There are a number of blue colored wires here. Are you talking about the Blue/Purple and Blue/Black ones that are going to the motor connector? No power there simply means the relays aren’t engaging, because they’re not being told to engage. You’ve swapped them and OHMed them and they seem ok… so we’re really talking about what’s happening on the control side of the relay… pins 86 to 85. With the ECU out, and disconnected, you should see +12V on the Blue/Green and Blue/Orange wires on the connector (as circled in red). The ECM will turn ON the relay by providing a ground pathway for that +12V to complete the circuit to ground (thus energizing the relay - one direction or the other - and powering the top motor - in one direction or the other).

We know the ECM provides grounding for the WINDOW relays, but we’re not so sure if it’s grounding on pins 2 and 3, and why since all the other checks so far seem OK.

There seems to be key-on power to the White and White/Pink wires to the ECM. I assume at least ONE has to be working for the ECM to be able to move the windows… but what if it needs one for the windows and one for the top? IDK. Worth a quick multimeter check…

~Paul K.

Well, at one time when I checked the motor as connected did not work. I then connected power directly to the motor and it did work. I reconnected everything to strat to pull the ECM and decided to try the top again.

IT WORKED !!! who knows what was wrong either initially or as I tested it, but that was good news. I assume it somehow was a lose wire. But it is a Jaguar so I will not ask further.

I really appreciate the help with this issue and I have learned a lot with all of your help.

Now on to the gas smell in the trunk.


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