Wow... The electrical gremlins attack!

[Moxie]

Jésus Christo. This is insane. So I just picked up a new (to me) 1989 325i. Did a full tune up and such, the motor is running like a champ (for an M20). But holy cow, this thing has electrical gremlins out the wazoo. I searched all over Google and looked through a couple dozen threads here, but if I missed something pertinent, I apologize! Feel free to point me there. Anyway - Here's what's up:

1. My gauge cluster isn't lighting up at all. (No, it's not a fuse. No, it's not burned out bulbs [see #2 for more info].)

2. Up until a few days ago, my turn signals worked fine (aside from not blinking on the gauge cluster). Now, if I signal, my gauges light up, but my signals don't work??? WTF is this sh!t.

3. My speedo isn't working. All my other gauges work properly.

All of the fuses have been replaced. I know little to nothing about electrical stuff. The best I've done is install a CD player. So speak simple to me, please! Thanks in advance!

[MoreMayhem]

Search around for the electrical troubleshooting manual (ETM) for your model. They are freely abundant on the interwebz. Get a circuit tester. Work through one problem at a time.

Edit: also read up about electronic circuits, relays, wiring diagrams.

[absolutdog]

For your speedo prob check the wires coming off of part #8 in the diagram

For your blinkers... R your cluster light blinking fast or slow??? how do the hazards behave??
check the shared ground between the blinker and the side marker.... buried behind the front bumper

[Moxie]

Search around for the electrical troubleshooting manual (ETM) for your model. They are freely abundant on the interwebz. Get a circuit tester. Work through one problem at a time.

Edit: also read up about electronic circuits, relays, wiring diagrams.

Got one of those manuals. It's all gibberish to me, man. And I'm a grad student, so although I'd like to take your advice and read up about all that stuff, it'd take me months. Was really hoping someone had a similar experience and could chime in.

Blinkers are something I can't do without. ATL drivers would have no clue what was happening if I used hand signals. They'd probably think I was flipping them off or something.

For your speedo prob check the wires coming off of part #8 in the diagram

For your blinkers... R your cluster light blinking fast or slow??? how do the hazards behave??
check the shared ground between the blinker and the side marker.... buried behind the front bumper

Now that I can do!

Right now, nothing with my blinkers works at all. Perhaps I should have added that my right blinker was blinking fast before this happened. However, they were never lit up on the dash. I could hear the clicking and the exterior blinkers lit up properly, but I've never had working lights on the gauge cluster. Last I checked the bulbs are good, but I can give that another double check today.

Thank you guys for the help!

[brianao34]

Grad student in what?

[Moxie]

Grad student in what?

Not sure why that matters, but... Experimental psychology. No, I don't fix crazy.

[Gregs///M]

Speedo and odometer not working is a sure sign the cluster is not getting speed signal from the rear differential sensor. Check to make sure all the plugs are connected to the cluster with nothing left out. Everything should be obvious where it plugs into.

Double check the speed sensor in the rear diff. Disconnect plug and check condition of the conductors and make sure they are not oxidized or corroded.

Verify your blinker bulbs are good. Fast blinking means the bulb is out. I would start there. Same with the cluster bulbs...how do you know they are good? Did you test them on a 12V circuit?

If you suspect any problems with the cluster, I rebuild them. I can go into more details but you need to check those bulbs first.

[brianao34]

Not sure why that matters, but... Experimental psychology. No, I don't fix crazy.

Just checking, if it had been an engineering degree it'd be different. Carry on.

[Moxie]

Speedo and odometer not working is a sure sign the cluster is not getting speed signal from the rear differential sensor. Check to make sure all the plugs are connected to the cluster with nothing left out. Everything should be obvious where it plugs into.

Double check the speed sensor in the rear diff. Disconnect plug and check condition of the conductors and make sure they are not oxidized or corroded.

Verify your blinker bulbs are good. Fast blinking means the bulb is out. I would start there. Same with the cluster bulbs...how do you know they are good? Did you test them on a 12V circuit?

If you suspect any problems with the cluster, I rebuild them. I can go into more details but you need to check those bulbs first.

I'll try to get to the cluster and speed sensor today. Thanks for the tip on that!

The bulbs in the cluster all come on when I have the headlights on and my turn signal stalk in the up OR down position, but I'll go ahead and replace them anyway while I have it out.

I have an update on the blinker. When I put the hazards on, the right blinker blinks (really fast). But neither (left or right) blinks when I move the stalk. Also, I just replaced of the bulbs yesterday morning. While I was doing that, I noticed a couple of anomalies. The rear and front marker lights were unplugged. Not sure if that would make any difference or not.

Thanks again, for all the help with this Greg!

Just checking, if it had been an engineering degree it'd be different. Carry on.

Fair enough.

[MoreMayhem]

I feel your pain. I've had electrical problems with other cars, and was able to weed through them with just a bare minumim knowledge of car electronics and a few simple tools.
No grad degree for me, just a BA in Communications!
Don't know if anyone mentioned it, but check all of your ground points too. There are a few scattered around the car. When you think you have found one, it will usually be several brown wires coming together in one spot that are bolted to the chassis. Make sure you have clean, solid grounds.

[Moxie]

Okay, I have some trouble shooting updates.

Checked the gauge cluster. All seems to be fine. Everything is connected where it should be.

The speed sensor is connected, but I haven't had a chance to pull it and clean off the connections. Is the sensor on the 325i the same as 325e and/or does anyone have the part number on hand? Google is showing up multiple speed sensors, and it could be a couple of days before I get to pull it.



^^Could this possibly be the reason that my signals are jacked? I removed the bumper today, and was kinda surprised when it just popped out and fell to the ground.

Also, what is the correct type of fuse for our cars? I've found mixed results googling this. Should I use open or closed fuses?

[Gregs///M]

The wiring looks pretty mangled so yeah, it could cause intermittent shorting. Repair that wiring and replace any blown fuses. Use the same type (blade) fuses from any auto parts store.

Speed signal comes from the sensor into C2 (white connector, ) brown/red stripe. It should have a pulse signal while moving. You can use a digital multimeter connected with the AC volts setting. You should see 1.5-6 volts AC while moving or applying power to the rear wheels while on jack stands.

If you verify this, (clean contacts at rear diff first,) and it does not solve the problem, you will need to have the speedometer repaired or replaced. Give me a PM if you need it tested.

[Moxie]

The wiring looks pretty mangled so yeah, it could cause intermittent shorting. Repair that wiring and replace any blown fuses. Use the same type (blade) fuses from any auto parts store.

Blown fuses have been replaced. I used ATC's, but that was based on immediately available (i.e., not necessarily reliable) information acquired while at Advance Auto. After digging around, I'm seeing a lot of ATO's in pictures of fuse boxes.

Speed signal comes from the sensor into C2 (white connector, ) brown/red stripe. It should have a pulse signal while moving. You can use a digital multimeter connected with the AC volts setting. You should see 1.5-6 volts AC while moving or applying power to the rear wheels while on jack stands.

If you verify this, (clean contacts at rear diff first,) and it does not solve the problem, you will need to have the speedometer repaired or replaced. Give me a PM if you need it tested.

I should be able to get to testing the speed sensor tomorrow afternoon/evening. Will update then. I'll give you a shout if I need anything! Thanks, again!

[Moxie]

Alright. I switched all the fuses to ATO's. Not sure if it helped anything, but whatever... it's done.

Checked the speed sensor. Ground wire was cut (it was brown, so I presume it was a ground). Spliced it up. Speedo works! However, I didn't mention it before because I figured that my cruise control was causally related to the speedo not working, and apparently it's not. So I'll mention it now... My cruise control also no worky! All my fuses are good. Any trouble shooting advice? Google searches haven't been incredibly productive on the matter.

Edit: Seeing a lot about the brake switch. Might give that a shot, if no one else has any better ideas.

Turn signals still aren't working. As best I can tell, all of the wiring to the lights is good, and I've replaced every single bulb. I've also replaced the relay. Basically, I've replaced everything except the turn signal stalk. I guess that's what I'll try next. I was wanting to do the 13 button OBC conversion anyway.

One thing I've also been meaning to ask about is going back to halogens from HID's. The previous owner did an HID conversion. I don't mind HID's if they work properly, but I've never noticed a huge difference in the HID versus halogens (seems like the most noticeable difference is in the use of a projector lens; not the bulb). Anyway, I digress. Is it easy to switch back? These things have never consistently worked right.

[t1xj]

i know this thread is from a bit ago, but i've been looking all over for answers...

my speed sensor wire is broken pretty close to the plug and in generally bad condition, so i'd like to replace it but i can't find the part number for the wire set... did you find one or did the splice fix you did mean you don't have to find a new wire set? found the sensor that plugs into the diff but can't find the wire set. or maybe i did but didn't know i had found it.

if you or anyone know the part number of that wire set i'd really appreciate it.

my problems are similar, no cruise, no speedo, no odometer, all other gauges work.