Battery discharged after driving with no gauge cluster - PeachParts Mercedes-Benz Forum

locry · #1 05-31-2011, 07:18 AM

87 300TD

Is it related? I drove my car to work this morning with the gauge cluster off... as I am in the middle of an evap retrofit.

As I started the car later in the afternoon it seems my battery was drained. I'm sure nothing was left ON. Only thing I can think of that's different is the fact that the gauge cluster was absent.

Thoughts anyone?

If it were the case... which pins should I bridge on the big round connector?

btw, I removed the battery and had it charged, starts just fine now... if i'm to attempt to head home I'd want it charging... so which pins if ever?
Thanks

barry123400 · #2 05-31-2011, 07:23 AM

Yes with the cluster out the warning light that is part of the charging circuit is disabled. So the alternator of course does not charge. The voltage that flows through that bulb activates the alternators magnetic field.

You would have to place a bulb into the circuit if you wanted to charge with no cluster and have a charging alternator. I am not sure if just shorting the two terminals is a good ideal where the bulb was connected to..It may do no harm but I am undecided so would play it safe.

locry · #3 05-31-2011, 08:30 AM

Thanks for the info! At least it's just a minor issue.

funola · #4 05-31-2011, 09:16 AM

Rather than trying to find which in in the cluster, it may be easier to clip a bulb from the small terminal on the alt to batt + termina to get the excitaation voltage.

vstech · #5 05-31-2011, 09:47 AM

that's why I like the 126 cluster, the alt and a few other lights are separate...

JHZR2 · #6 05-31-2011, 10:05 AM

Agree, your alt will not excite to charge. I'd get a good charger on that battery right away or risk permanent capacity loss.

locry · #7 05-31-2011, 10:54 AM

it's been charged already, I might opt to drive during daytime so I won't need headlights. The only draw that probably discharged the battery this morning was the permanently on aux fan.

vstech · #8 05-31-2011, 05:40 PM

... it's 99 here with 80% humidity... what's it like near you?

locry · #9 05-31-2011, 10:27 PM

I have no idea what the figures are but its sweltering hot... plus the fact that my evap is off, and I forgot to install the plastic covers and weather strips under the hood/wiper... engine heat is invading my space!!!

anyway, I'm still at the office, for at least 2 more days, gauge cluster is at home, what, if any, can I bridge to restore charging?

Jeremy5848 · #10 05-31-2011, 11:50 PM

Quote:

Originally Posted by locry

I have no idea what the figures are but its sweltering hot... plus the fact that my evap is off, and I forgot to install the plastic covers and weather strips under the hood/wiper... engine heat is invading my space!!!

anyway, I'm still at the office, for at least 2 more days, gauge cluster is at home, what, if any, can I bridge to restore charging?

OK, I have one of those, the sedan version anyway, and all of the electric diagrams. All you need is a lamp and a diode. You can get the parts you need at any electronics store. If you have connections at a company that has an electronics lab, they will probably have what you need in their own supplies.

The lamp and the diode are connected in series and wired between pins 8 and 9 of the round 15-pin plug that you removed from the instrument cluster. All you have to do is twist together one lead of the diode and one lead of the lamp and stick the other leads in the pins of the 15-pin plug. The components must be in the following direction (the lamp can be installed either way but the position of the diode is critical). Don't let any of the wires touch the chassis.

Pin 8----Lamp----Diode with arrow --->|----Pin 9

If the diode has an arrow (diode symbol " ->|- "), the arrow points toward Pin 9. If the diode has only a line or bar on one end, the line or bar goes towards Pin 9.

Just about any garden-variety semiconductor diode will do. Some common part numbers are 1N4001, 1N4002, 1N4003. An electronics store will be able to cross-reference those numbers to what they have. Basic spec would be something like 1 Amp at 100 PIV.

The lamp can be any automotive or electronic pilot lamp rated 12 Volts at 0.25 Amp (about 3 Watts). Do Not Use An LED!

With this jury-rig connected, the lamp should light up when you turn the key to the pre-glow position. Once the engine has started and the alternator is working the lamp should go out.

Jeremy

locry · #11 06-01-2011, 05:26 AM

ey cool! Thanks for the instructions!

I'll try to scrounge a diode somewhere here in the office.