so i bypassed my rheostat...... - PeachParts Mercedes-Benz Forum

IVIuzzy · #1 01-25-2011, 07:44 PM

my cluster lights werent working on my 73 220d, so i bypassed the rheostat. now they work!.....kinda.

i tested, with a continuity tester, power to the posts where the rheostat was, and power is going. now when the lights are lit until i move the cluster, they flicker depending on where how its mounted. where is the ground? it seems to me like there is a bad ground however its difficult for me to stick my fat head between the wheel into the cluster hole. thanks for any input on my dilema!

IVIuzzy · #2 01-25-2011, 09:35 PM

i tried messing with it a little more now im kinda PO'd at it so im going in for the night,

so far ive popped 3 fuses and the lights arent coming on anymore, im normally very good with electronics but for some reason i cant figure this out, power is going to the rheostat post but for some reason the lights are not coming on(i know theyre dim as it is but theyre def not on) with all new bulbs. i feel like im missing a ground somewhere.

all im doing is connecting the main harness, and theres 2 ground posts that go on right by the speedometer. am i for some reason missing something? i know somethings shorting as im popping fuses.

Kpmurphy · #3 01-26-2011, 02:08 PM

w115 Electrical woes (instrument cluster lights?)

This might help I have a picture on the 3rd post.

meltedpanda · #4 01-26-2011, 03:06 PM

whenever I mess with a dash pod in these , I run a ground line to the dash frame from the pod frame.
I know on my 72 the frame grounds with the pod and you have to get it in there just right, so I just run an extra ground wire and its fixed.
Also sometimes the traces get broken and need reflowed or by passed with a jumper , check those closely

IVIuzzy · #5 01-26-2011, 05:04 PM

i today realized that the fuel gauge is inop and the back of the cluster is damaged. i dont know if there is a short somewhere in the cluster itself. ill try to run a whole new ground but the local scrap yard wants 35 for a cluster without the speedometer.

how do i get the temp gauge disconnected from the cluster? the large braided wire it seems like its part of the gauge itself. thanks

meltedpanda · #6 01-26-2011, 07:31 PM

hmm, can you post a picture, thought there were just 2 nuts?

79Mercy · #7 01-26-2011, 07:34 PM

The temp gauge on this car is mechanical, not electrical. That is a braided tube filled with ether. You must disconnect it under the hood and pull it out from inside the car.

Try running a ground wire from the back of the speedometer to the body of the car.

IVIuzzy · #8 01-27-2011, 09:20 AM

so if the cord from the scrapyard was cut, i need to reuse my old gauge?

IVIuzzy · #9 02-01-2011, 09:23 PM

79 mercy... are u sure its ether. my indy said theyre filled with mercury.

at any rate heres what i think happened. the tube was kinked that was for my temp gauge, and leaked the mercury, or ether, all over the circuit board for the cluster.

if it is infact mercury, mercury is conductive and thats what is shorting out my board. (u can see the stain on where it hit the board and dripped everywhere)

so tomorrow im going to the scrapyard to see if i find a gauge that the tube has not been cut.

ill keep u posted.

neubob · #10 02-01-2011, 11:06 PM

2 things. whenever i had a bad rheo i just stuck a wire into the 2 holes that are like long pop rivets u can't adjust u r just at max. # 2 if u can't find temp guage i should have one.

79Mercy · #11 02-01-2011, 11:18 PM

Im pretty sure its ether, that's what was always used back in the day with the mechanical temp gauges on US cars.

WANT '71 280SEL · #12 02-01-2011, 11:31 PM

I bypassed the rheostat in my 116 and I could swear that the lights are brighter than they ever were with a working rheostat. Older Mercs all have poorly lit instrument clusters so I'd find a way to bypass it if at all possible. Then again, this of course doesn't address your capillary tube issue (line going to the temp sensor).

Best Regards,

David

JMela · #13 02-02-2011, 12:18 AM

Here's an easy way to bypass the rheostat - check the bottom of the page:
http://www.sl113.org/wiki/Electrical/Rheostat

250 Coupe · #14 02-02-2011, 04:26 AM

Quote:

Originally Posted by IVIuzzy

79 mercy... are u sure its ether. my indy said theyre filled with mercury.

at any rate heres what i think happened. the tube was kinked that was for my temp gauge, and leaked the mercury, or ether, all over the circuit board for the cluster.

if it is infact mercury, mercury is conductive and thats what is shorting out my board. (u can see the stain on where it hit the board and dripped everywhere)

so tomorrow im going to the scrapyard to see if i find a gauge that the tube has not been cut.

ill keep u posted.

Mercury would not have left a stain. Every gauge I've come across has been filled with ether.

Here is a pretty informative thread about temp gauges,
http://www.british-cars.net/mga-bbs/temp-oil-guage-repair-2010070122184630000.htm

And here is a link for repairing a gauge using an aftermarket gauge as a donor.
http://www.ply33.com/repair/tempgauge

Michael

IVIuzzy · #15 02-07-2011, 10:15 PM

i got a junkyard cluster, with a working rheostat so that issue is solved.

there were no clusters with the temp gauge "hoses" in tact, so i bought a cluster from a 1976 300d, with an electrical temp gauge, took the sender from the block, and just added the wire into my wiring harness.

now i have an electrical gauge