Temp gauge not working - bad sending unit?

[Babe Tomahawk]

I've searched through several threads on r3vLimited as well as a few google image searches. I'm trying to diagnose a non-working temp gauge on my 1986 325 (ETA car), here are my questions...

Which sending unit in the attached pic is ties into the gauge? I've read on a couple threads it's the "brown" one, but I have a couple brown ones.



I've Ohm'd out the sensor (forward most in the pic) and I get resistance, so I'm not sure that's the issue.

The gauge needle doesn't even flinch when I turn the ignition on (like this) would that be indicative of a busted gauge? Dead SI batteries?

Just looking for a little advice on which direction I should head before I start throwing money at the problem.

Thanks in advance-
E30 Newb

[modernist]

With the ignition on, ground the wire going to the temp sender. The gauge should go full hot. If the gauge doesn't move either the wire is broken or the gauge is faulty. If the gauge does move, just replace the sender. There are also two 7mm grounding nuts on the back of the cluster -- these work their way loose and cause jumpy/erratic readings. Tighten them up and see if it helps.

[audiquattrot]

if you need a gauge lmk. I have one for sale.

[Babe Tomahawk]

modernist - thanks for the tips! I'll be trying this tonight when I get home.

audiquattrot - thanks for the offer, I'll let you know if I'm in need of one.

[randomtask37]

I fought this issue for over a year only to find an almost broken wire near the sensor that was causing erratic signal - mostly no signal.

Check the wire and try a junk yard sensor.

I had both a dead sensor and bad wore.

[packratbimmer]

The big brown one is the thermal time switch for warm-up enrichment.

[Babe Tomahawk]

So there might be another twist to this non-working temp gauge thing...I pulled my gauge cluster to check the grounding nut on the backside (and to repair the odo gears) and found there is no SI board what so ever... this could be a problem no?