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Old 12-27-2009, 05:01 PM
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Join Date: Aug 2005
Location: Palmdale/Ventura, CA
Posts: 813
Two temp sensor leads, one temp sensor

My 1980 300D wiring harness has two leads/connectors
for two temp sensors in the engine head.

My 1981 donor engine only used one sensor.
I tried hard to get the plug out of the 1981 engine head so I could
add the second temp sensor, but this never happened.

So, I have one sending unit and two sensor leads.

Over the years I have tried:
1. Leaving the unused sensor lead unconnected.
2. Connecting a sending unit to the unconnected sensor and left it hanging there.
3. Running a wire from both sensor leads to the one sending unit.

I have mentioned before that my engine temp is a dead on 80C as checked
with a mercury thermometer in the radiator and using a infrared thermometer.

My dash gauge has started reading higher than 80 recently.
Looking for clues.

I swapped the sensor from the 300SD into the 300D and am seeing a
high reading dash gauge still.

Someone here mentioned adding a ground wire to the instrument panel
and I am working that out now.

Any suggestions on what to to with my unused temp sensor lead ?

80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250
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Old 12-27-2009, 05:55 PM
Registered User
Join Date: Jan 2002
Posts: 18,355
One of those sensors controls how long the glowplug light stays on dependent upon temperature. Other than that it plays no role so isn't really necessary.

1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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