Can an aftermarket head unit cause gauges not to work

[Appleseason]

Hello,

I'm new to r3v and haven't found much information on this topic.

I recently bought an E30 to swap as my first big project, and the original M20 engine blew because the temp gauge wasn't working, and the previous owner did not fix it. I looked into it, and all of the connections on the temp gauge seem to be clean, but I still sanded the three poles that go into the cluster. The test from the Bently Manual of grounding the brown/purple wire has yielded no results on the original cluster I have, and on a new one I found from a junkyard.

A few days ago, I was reading up on some things and found a person who claimed that a bad install of a head unit caused random gauges to stop working.

My question would be if anyone has any information on the wires that may be involved in this issue, thank you.

[TimeMachinE30]

Yes, a FUBAR install could cause many other things to be FUBAR.

[Appleseason]

Yes, a FUBAR install could cause many other things to be FUBAR.

So today I removed and unplugged the aftermarket head unit, the same problem persists, which I find strange. I did try another beet up cluster, and had the same results of all the gauges but the temp gauge working. I don't suspect the instrument panel to be the issue since the one in the car right now is very clean and doesn't have any obvious damage.

I will keep looking.

[IceWhite]

Few questions.
What actually happens to the gauge, Is it completely dead? Does it work intermittently? or does it bounce around?

[AndrewBird]

Could be a bad temp sender on the engine. Hard to tell if the gauge is working without running the engine up to operating temp.

Also, simply unplugging the stereo won't fix bad wiring job. What usually happens is people splice into things they should and cause other things to stop working. Only way to fix it is to return it to stock and wire the stereo properly.

[Appleseason]

Few questions.
What actually happens to the gauge, Is it completely dead? Does it work intermittently? or does it bounce around?

When the engine is started, the needle jumps to the "cold" part of the gauge. It does not jump around. When I removed the instrument cluster for cleaning I found with my continuity tester that if I jump one of the poles to ground or to the other pole, the needle jumps from "cold" to "hot" with no issue.

The issue is that the test from the Bentley manual of grounding the brown/purple wire to make the needle jump to hot is not working under any circumstances.

[Appleseason]

Could be a bad temp sender on the engine. Hard to tell if the gauge is working without running the engine up to operating temp.

Also, simply unplugging the stereo won't fix bad wiring job. What usually happens is people splice into things they should and cause other things to stop working. Only way to fix it is to return it to stock and wire the stereo properly.

I have gotten the engine up to operating temp before with the gauge not responding at all, the previous owner had the same issue.

My swap currently has a brand new brown top e30 sensor in it, and I checked the resistance on it while the engine was heating up before, and it seamed perfect.

The issue persists that the Bentley manual test for the gauge of grounding the brown/purple wire is not working.

[TimeMachinE30]

I have gotten the engine up to operating temp before with the gauge not responding at all, the previous owner had the same issue.

My swap currently has a brand new brown top e30 sensor in it, and I checked the resistance on it while the engine was heating up before, and it seamed perfect.

The issue persists that the Bentley manual test for the gauge of grounding the brown/purple wire is not working.

Trace the wire.

Bet its related to radio "upgrades:".

[Appleseason]

So an update, I took out the head unit and found all kinds of things wrong. One question i have is what is this green wire that is going into the body, I've tried google and found nothing.

http://i.imgur.com/56wrk3X.jpg

[IceWhite]

When the engine is started, the needle jumps to the "cold" part of the gauge. This shows the cluster is getting power. It does not jump around. This shows your grounds are good. When I removed the instrument cluster for cleaning I found with my continuity tester that if I jump one of the poles to ground or to the other pole, the needle jumps from "cold" to "hot" with no issue. This indicates your gauge is functioning.

The issue is that the test from the Bentley manual of grounding the brown/purple wire to make the needle jump to hot is not working under any circumstances. This is where your problem is. Your cluster is getting power but it is not getting the signal to show how hot the engine is getting from startup until operating temp.

Ok, so as TimeMachinE30 stated, you need to trace the wire. The wire in question is usually a Brown/Violet (or purple) wire that starts from your brown temp sender. It then goes through the C191 Connector (Pin 4) then to C101 connector (Pin 4) then to the cluster Blue plug (Pin 26). This info is correct for my car which is a 1990 model 325i and with a motometer cluster. Download the ETM for your car and confirm the wire color and pin positions all the way from the sender to your gauge. If yours are the same, you can now check for continuity along the wire as you can see there are a lot of connectors that can be corroded and cause the connection to be broken.

[Appleseason]

Ok, so as TimeMachinE30 stated, you need to trace the wire. The wire in question is usually a Brown/Violet (or purple) wire that starts from your brown temp sender. It then goes through the C191 Connector (Pin 4) then to C101 connector (Pin 4) then to the cluster Blue plug (Pin 26). This info is correct for my car which is a 1990 model 325i and with a motometer cluster. Download the ETM for your car and confirm the wire color and pin positions all the way from the sender to your gauge. If yours are the same, you can now check for continuity along the wire as you can see there are a lot of connectors that can be corroded and cause the connection to be broken.

That makes sense, I did check for continuity with my little tester from the brown and purple wire that plugs directly to the sensor and to the pin on the blue plug and the continuity is fine. The issue is that the previous engine, and engine harness had the same problem.

I will double check again today.

[TimeMachinE30]

With all the work done to this car you are claiming, I'd suggest tracing the wire. Get your eyes on it. The manuals may no longer apply if slim rigged up his own harness along with ICE mods.

[Appleseason]

An update.

As suggested above, I traced the brown/purple while from the plug on the cluster all the way to the place it plugs into on the motor. I put one small pin into the plug hole for the wire, and the other end into the little plug for the sensor on the engine, there was continuity.

The only thing I can think to do now is to find someone in my area with a known working cluster and try to ask them if I can momentarily swap it.

[IceWhite]

So now the brown/violet (brown/purple) wire does have continuity from the sensor until the female plug for the cluster, the only other place for a problem could be the main cluster board, main board solder joints, SI board batteries or the SI board itself. Have you replaced the batteries, or checked the voltage on them?

[Appleseason]

So now the brown/violet (brown/purple) wire does have continuity from the sensor until the female plug for the cluster, the only other place for a problem could be the main cluster board, main board solder joints, SI board batteries or the SI board itself. Have you replaced the batteries, or checked the voltage on them?

I have not, I will do that later today, I have a suspicion that the board may have something wrong with it, so I will go through it. Are there any guides on replacing SI batteries? I will look.

Thank you