'91 500SL heated seat problem

[Olly]

Hi chaps, newbie here.

The driver's seat heater on my 1991 500SL has just started playing up.

The backrest heating works as normal, but the heating in the seat base has failed.

The passenger seat works as normal.

Any ideas?

 

[talbir]

Hi,

This is most likely to be the relay, which is usually located under the seats. Since your backrest is working, there is no problem with the switch.

First check the connection to the element, which can be found under the seat - there are 2 two-prong black connectors under the seat which control the heated seat elements. One for the base, one for the backrest. Check the integrity of the connections.

Both terminals in each connector should be ground at rest and when heated seat switch is pressed, the terminals change to supply a +12V and ground for the element. Check the connectors are giving out the right signals.

Using a tester, find which one is working - then swap over the connectors. If swapping over, results in your base warming up and not your backerst, then you know it's your relay.

The relay is fairly expensive, approx £95 +Vat. On later cars there is usually just a single relay which controls both front seats.

You should be able to adjust the seat to maximum height and work without removing the seat.

It is very unlikely to be the heating pad itself - but gear up for some hard work if it is......you'll need to remove the seat, remove the base leather cover, fit a new element and then refit seat cover etc etc. A new element is approx £60.


Hope this helps.

 

[Olly]

Great information talbir, thanks for your help.

 

[Olly]

Had an investigation: could only find one black 2 pronged plug (located at the back of the seat) on each seat.

Unplugging the black connector made no difference on the drivers seat, the backrest still warmed but the squab did not. Undoing the same plug on the passenger seat killed the squab heating, so this must be the correct connector for the squab heater..

The connector becomes live once the switch is pressed on, so I take it that the relay is defective.

Anyone know where the relay is located, under the seat or elswhere?