W124 woes - self test lights

[16simon]

Hi all, I've just bought a low mileage W124 230E (78k) that should be a good un but has a few niggles that need to be sorted out first.... I had the head gasket replaced (unfortunately it didn't start burning coolant until after I'd bought it) by my local garage and hoped that nothing else would need doing.

However, the self test lights do not illuminate when the ignition key is turned prior to startup. I pulled the instrument cluster (after a lengthy struggle) and all the bulbs are ok. I know that the low coolant light works (it came on when the engine was burning through coolant before the HG was fixed) so after doing some internet research thought that a faulty voltage regulator might be knocking out the self test system. I fitted a new VR but the battery still only shows just over 12v when the engine is running. I've driven the car about 150 miles though, and the battery hasn't died on me which gives me some hope.

Any idea what the problem might be? Is it possible that I've been given the wrong replacement VR? Would appreciate any suggestions

 

[television]

There are not any self test lamps. when you turn the ignition on the battery charge lamp must be on, and this goes out if the alternator is charging, if the lamp has failed the alternator cannot charge as this is fed to the exciter wire on the alternator that starts the charge

 

[16simon]

Hi Television, I didn't explain that really well, I meant that I'd expect the battery light, oil pressure light, etc to illuminate until the engine fired up - but they don't, the handbrake light and ABS light are the only ones that illuminate.

I removed all the bulbs (including the one for the battery charge light) and they all work.

Is there anything else that I can check?

 

[huey]

Hi There, double check the bulbs, also make sure the contacts on the back of the cluster are nice and clean, I dont know if the 2 you have working are on a seperate fuse, but it will also be worth checking all fuses, wiggle them all one at time, may also be worth cleaning the fuse holders 1 at time.

 

[television]

Hi Television, I didn't explain that really well, I meant that I'd expect the battery light, oil pressure light, etc to illuminate until the engine fired up - but they don't, the handbrake light and ABS light are the only ones that illuminate.

I removed all the bulbs (including the one for the battery charge light) and they all work.

Is there anything else that I can check?

You could have a broken wire or poor connection on the very thin wire that goes to the alternator, this goes to the lamp

this is the circuit diagram
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1993/300E/SYSTEM WIRING DIAGRAMS/4513.pdf

 

[16simon]

Thanks guys!! I'll check all the fuses (from memory, they're all slightly corroded on the ends so in need of a clean anyway) and see if I can get the battery light to illuminate by grounding the thin wire on the alternator plug (I think this is right?) - that should give me more of an idea of where the problem is.

Will report back tomorrow....

 

[DIYMAN]

Congratulations on your purchase, should turn out to be a great car, just make sure you keep the coolant mix up to strength to protect the cylinder head.

Did the dash board lights work as expected before the new head casket was fitted, I am thinking maybe all the wiring loom has not been reconnected properly?

 

[balge59]

Hi Television, I didn't explain that really well, I meant that I'd expect the battery light, oil pressure light, etc to illuminate until the engine fired up - but they don't, the handbrake light and ABS light are the only ones that illuminate.
I removed all the bulbs (including the one for the battery charge light) and they all work.
Is there anything else that I can check?

ABS light stays on, try checking the OVP relay and it's fuse (under the plastic flap behind the battery) - if the alternator is definitely charging properly?

 

[16simon]

Thanks everyone, all the suggestions are really helping

The ABS light doesn't stay on - and I don't think it's the OVP since the car starts and runs smoothly.

Good point DIYMan - I only drove the car for a week before it went in for a head gasket (unlucky, I know) so can't remember whether the warning lights worked before. The car has been making tappet noise since the head was done so it needs to go back to the garage for this to be looked at - if I haven't worked out what's up with the electrics before then I'll get them to look at this as well.

 

[star]

Check the voltage reg has good contacts or as above with small wire to alt. all the lamps should light when the ign is turned on as a test of their function.

 

[16simon]

As soon as it was light I was under the bonnet.... I tested the connector at the end of the small wire to the alternator and wasn't getting any voltage. I followed it back to a junction block and tested it there.... 12v with the ignition on!!

I then connected a new wire from the junction block to the connector on the alternator, took a deep breath, and turned the ignition key and..... all the warning lights illuminated

Thanks a lot for the help everyone: I'm really pleased because:

I've learned something new about how the alternator works
I've fixed the problem myself
It hasn't cost anything

win - win - win!!!

 

[television]

As soon as it was light I was under the bonnet.... I tested the connector at the end of the small wire to the alternator and wasn't getting any voltage. I followed it back to a junction block and tested it there.... 12v with the ignition on!!

I then connected a new wire from the junction block to the connector on the alternator, took a deep breath, and turned the ignition key and..... all the warning lights illuminated

Thanks a lot for the help everyone: I'm really pleased because:

I've learned something new about how the alternator works
I've fixed the problem myself
It hasn't cost anything

win - win - win!!!

What a nice post,, thank you

 

[huey]

Brilliant Glad to hear it was a simple fix.

 

[teddycatkin]

Thanks everyone, all the suggestions are really helping

The ABS light doesn't stay on - and I don't think it's the OVP since the car starts and runs smoothly.

Good point DIYMan - I only drove the car for a week before it went in for a head gasket (unlucky, I know) so can't remember whether the warning lights worked before. The car has been making tappet noise since the head was done so it needs to go back to the garage for this to be looked at - if I haven't worked out what's up with the electrics before then I'll get them to look at this as well.

They have re-filled it with oil when head was off ?-hence tappet noise ?