Replacing External Temperature Sensor - 107 Series - Any pro

[Malcolm Brown]

The external temp dial on my 1988 SL constantly reads max temperature. I have assumed the sensor is a simple thermistor which is faulty (shorting) and have got hold of a new one (the MB part number is not 107-specific). It has a long cable (2 wires) attached with a plastic connector on the other end. This connector is different from the one at the back of the meter, which has 4 wires. The new sensor also came with a small packet containing 3 pairs of small aluminium pin-type devices in different sizes and a small rectangular plastic thing that looks like a connector of some sort - no idea what those are for.

There must clearly be a connection in the cable - to introduce power via the two extra wires - but I can't find it. The cable from the sensor, which is behind the front number plate, runs into a bundle of wires and I've not managed to trace it right through. Please does anyone know whereabouts the connector is?

If I can't find it, or if it is somewhere difficult to access, can anyone think of a reason why I should not just cut and join the existing cable to the new? Provided I make a very good connection and don't change the length of the wires, then it shouldn't affect the calibration significantly. There's about 3 metres of wire so I reckon that if I match the cable length as closely as I can, the change in the total resistance of the wire should be very, very small - certainly less than 1%. Of course, this is only a theory - and it fails completely if the problem isn't a faulty sensor!

PS. One day, I hope I'll be able to answer a question - I'm just asking them at the moment. But there's lots of fascinating reading and some very helpful people in these forums.

 

[Anthony Banos]

Replacing External Temperature Sensor - 107 Series

Quote: from Malcolm Brown on 12:06 am on Jan. 11, 2002
The external temp dial on my 1988 SL constantly reads max temperature. I have assumed the sensor is a simple thermistor which is faulty (shorting) and have got hold of a new one (the MB part number is not 107-specific). It has a long cable (2 wires) attached with a plastic connector on the other end. This connector is different from the one at the back of the meter, which has 4 wires. The new sensor also came with a small packet containing 3 pairs of small aluminium pin-type devices in different sizes and a small rectangular plastic thing that looks like a connector of some sort - no idea what those are for.

There must clearly be a connection in the cable - to introduce power via the two extra wires - but I can't find it. The cable from the sensor, which is behind the front number plate, runs into a bundle of wires and I've not managed to trace it right through. Please does anyone know whereabouts the connector is?

If I can't find it, or if it is somewhere difficult to access, can anyone think of a reason why I should not just cut and join the existing cable to the new? Provided I make a very good connection and don't change the length of the wires, then it shouldn't affect the calibration significantly. There's about 3 metres of wire so I reckon that if I match the cable length as closely as I can, the change in the total resistance of the wire should be very, very small - certainly less than 1%. Of course, this is only a theory - and it fails completely if the problem isn't a faulty sensor!

PS. One day, I hope I'll be able to answer a question - I'm just asking them at the moment. But there's lots of fascinating reading and some very helpful people in these forums.

Hi Malcolm,

The temp sensor with the two wires (one blue & the other black-blue-yellow) are connected to pole 2 & 3 respectively of the 10-pole plug connector for tester in engine bay. The harness of wires is a tight bunch with many twists and bends and very difficult to extract old wires. Suggest you get 2m of plastic wire tubbing to shield the new wires and wrap it with ties at intervals on the wires harness to the 10-pole plug, disconnect the old ones and connect new ones and presto! (If you let me have your email address will attach wiring diagram

 

[Malcolm Brown]

Replacing External Temperature Sensor - 107 Series

Anthony

Thanks v much for reply & advice. The wires on the new sensor are brown & green - not checked originals yet, but connector is a one-way fit so should be no prob (unless they've supplied wrong part!)

I'd like to take up your offer of wiring diag, please. My e-mail address is malcolm.p.brown@ntlworld.com

 

[Anthony Banos]

Replacing External Temperature Sensor - 107 Series

Quote: from Malcolm Brown on 3:44 pm on Jan. 11, 2002
Anthony

Thanks v much for reply & advice. The wires on the new sensor are brown & green - not checked originals yet, but connector is a one-way fit so should be no prob (unless they've supplied wrong part!)

I'd like to take up your offer of wiring diag, please. My e-mail address is malcolm.p.brown@ntlworld.com

Malcolm

MB superseedes color coding .Regard green as black-blue-yellow. Emailed diagrams.

Regards

 

[Malcolm Brown]

Replacing External Temperature Sensor - 107 Series

I'm afraid I gave up on fixing it the proper way and cut and joined the wires, which has worked fine without affecting calibration.

I found several tester connectors (I think) but would have needed to dismantle them find the correct wires. Diag is for A/C system, which I don't have, so that didn't give an obvious answer. I was nervous about dismantling connectors in case any bits fell out and got lost! At least I now know that the little aluminium things that came with the sensor kit are new pins for the multi-pin connector.

Thanks for the help.