Need help finding power draw at interior light relay

[She loved E]

Spent a good chunk of the day trying to track down a 150 mA power draw on my 89, and got to a point where I'm not sure what to do next. Hoping someone here knows this stuff better than I do and can help me out.

I traced the draw to fuse 27, then the interior light relay (the one behind the front speaker next to the central locking unit). While I was in there, I noticed that the dome light is not coming on when either of the doors are open. I don't suspect the door switches or the relay, however, because when I press one of the switches, I hear a click from the relay. Doesn't that mean the switches and the relay are working properly? If so, do I need to start tracing wires to find the fault and/or power drain? Does anything else run thru this relay that I should also be looking into?

I've never gotten this deep in to troubleshooting electrical issues, so if anyone can give me some hints for where I should start looking next I'd appreciate it!

TIA

[She loved E]

Small update. I picked up a used central locking module and light relay today and tried both. No change. Still seeing voltage draw from the relay only.

In the midst of this I noticed that I only have one dome light... The passenger side light has been deleted, but wiring is still running there from the B-pillar. I'm gonna try looking into what is connected thru this relay... I wonder if not having the second dome light connected is part of the problem.

[george graves]

Small update. I picked up a used central locking module and light relay today and tried both. No change. Still seeing voltage draw from the relay only.

You lost me. No change? So you narrowed it down to the interior light relay? What if both are unplugged? Or just one?

In the midst of this I noticed that I only have one dome light... The passenger side light has been deleted

What do you mean it's been deleted? As in removed and there is a gaping hole there in your head liner you didn't notice? Or the factory didn't install it?

The factory interior light relay is a huge power hog - most people don't know that. With that said, when they fail (most) just stop working. But some just sit there and drain your battery and do nothing.

Last question - 150 mA isn't a ton of current, but it might be enough to feel the culprit getting warm to the touch on a cool day. Sp what's getting warm?

[She loved E]

Yep, I get draw when the relay is plugged in, when I unplug it draw drops to ~10 mA. If I unplug the central locking unit I still have the 150 mA draw.

The headliner is black, I'm guessing its not factory. Theres no hole for the passenger side dome light, thats why I didn't notice it at first.

The relay did feel slightly warm as I was disconnecting it. It was so slight though I didn't think it was noteworthy.

Its possible that both these relays are bad, I actually have a third I will try today. Is it reasonable to guess that all three might be bad and that I should just get a new one? I was starting to think that theres a wiring issue causing the drain (theres some hackey DIY wiring in this car), but maybe I'm better off getting a new relay to eliminate it as a variable.

[She loved E]

No luck from the 3rd relay. Will probably shelve this and check for a bad ground when I finish swapping the carpet & dash later this month. Thanks for the help George... will keep an eye out for any other ideas and post back when I figure it out.

[george graves]

You're not making this easy to read IMHO. Your last sentence was confusing at best.

This isn't rocket science - unplug things, and then you find a dramatic drop in amps, there's your issue!

[She loved E]

I'm happy to clarify anything that's not clear, George.

My amperage draw is at the relay. Does that mean the relay is causing the drain? Or is it possible that there's a connected bulb/ground/switch that could be causing the drain? If the former, I'll buy a new relay and call this done.

[Das Delfin]

^ what you want to do is download the electronic troubleshooting manual for your model year from wedophones.com and take a look at the wiring diagram and see what else is in that circuit. Then plug/unplug that stuff until you find the failed component.

It's possible for the relay to still click even if it has failed. But three failed relays in a row seems unlikely.

I just read.. janky wiring is a much more likely culprit than supposedly failed german parts. You will want to use the wiring diagram and correct any shitty wiring FIRST

[She loved E]

Good call... I have the manual, here's the offending circuit:



If I'm reading this right there's just two switches and grounds on this circuit.

[george graves]

The central locking does have a weird loop that feeds into it. And You could have a bad door "pin switch" that is crusty. If it was just the right amount of crust-ness, it could be constantly triggering the interior light relay.

There's also a micoswitch in the door (not seen in that pic of the ETK) that all have failed 20 years ago - it's the pin on the relay hat is the small one.

[She loved E]

Today i disconnected the relay completely and realized its no different than when its connected (dome light works in ON position, but not in doors open setting), except without the draw. Gonna run like this until I check for a bad ground.