W163: ML270CDi power seats not working.

[DexterML]

Hello all

The ML270 power seats are not working. The foot well fuse box was quite corroded. I took it out and cleaned it and installed a new relay. I have checked with a multimeter. I get 12 volts on the live side or the fuses.
I took the seat cover apart and measured the switch, I got four (4) wires going in and all show +12v, which makes no sense to me. I checked the cable to the under seat module and I get various pins with 12v.
Yet neither of the two seats will move.
I cannot apply 12v directly to any of the motors as I have very little space and I can't see what I am doing.

any ideas?
*passenger side switch also has 12v on all 4 pins going in.

 

[zipdip]

Well given you have power,do you hear the motor running,if not suggest you look at the switches that send the seats back and forward.

 

[DexterML]

Well given you have power,do you hear the motor running,if not suggest you look at the switches that send the seats back and forward.

Hi, thanks for your reply.
No there is no sound coming from the motors on either seat.
How do you mean look at the switches? I measured the switch connector and got 4 wires with 12v. What else is there to check? You mean take the switch apart?

What I don't get is how the switch operates with all 4 wires feeding 12v to it. I mean surely at least one should have been ground and this is the same for both switches.

 

[DexterML]

Correction : All 4 wires to the adjustment switch are grounded, not live.

 

[DexterML]

UPDATE:

The seats are working now. I was using a replacement generic relay which perhaps couldn't handle the load. I sourced some 2nd hand relays and now the seats are working.

cheers all

 

[zipdip]

Well done

 

[DexterML]

To finalize the update perhaps in case it will be useful to others in the future.

The car had major water ingress which messed up the footwell fuse box.
All snap on relay sockets were corroded and the relays were ruined.

I took the fuse panel out, cleaned (with dremel, and sanding paper) out all contacts and used a brush wire for the pins in the connectors to make sure corrosion remnants were gone.

Used generic similar relay (probably couldn't handle the load and although clicking, wasn't carrying any juice to the seats) --Avoid if possible generic relays.

Sourced second hand genuine relays.

Seats are working now.

It took a lot of work to pin point the source of the issue.


Thank you all