dead fuel guage, turn signal flasher

[Ed Fisher]

Two topics:
1)   While troubleshooting my turn signal flasher I inadvertently hooked up the large two connectors under the dash reversed.  The reversal causes the horn to blow, so it is easy to hear the mistake.  I mention this because my fuel gauge is now on empty no matter what.  I did a search and saw all kinds of cool stuff regarding differences in old/new floats etc, but I did not see anything about a completely dead gauge.  Did I possibly disconnect or knock off a ground?  If so, where does it go?  Did I possibly fry the gauge by connecting the two plugs up wrong?  Any help would be much appreciated.
2)   The turn signal flasher, round and silver, has been disconnected from Bosch.  Will Smith doesn’t know how to hook up the new, square flasher relay, nor can he get the old one from Bosch.  Will called Bosch and they do not have a recommended hook up for our Pagodas.  Ron and Jeff have helped me with replies, and Gernold verified the new wiring to the socket in the car.  Hopefully, I will be able to try it this weekend.  I would so love to contribute something to this list for a change.

Ed
Dallas, Texas

[jeffc280sl]

Hi Ed,  

Sorry to hear about the connector mixup.  We've all been there.  What starts out as a simple problem sometimes multiplies.  There are three wires connected to the instrument cluster fuel guage.  One wire comes directly from fuse 5.  Make sure you have power going to this connection.  The other 2 wires come from the sending unit and provide a ground reading to the gas gauge.  I would ohm out these wires so you know there good.  Assuming you have power at the cluster, if you provide a ground on the sender connector side at the pins you identified, one should you should illuminate the low fuel indicator light.  The other wire provides various resistance measurements to the gas gauge which indicates fuel levels.  About a week or so ago someone posted these measurements for empty and full gas tanks.  One could go to a radio shack store and buy resistors of these values and place the resistors in between ground and the gauge pin on the sending unit.  One should give you a full and the other an empty reading on the gas gauge.  If this all works the problem is in the sending unit.  Let us know what you see and we can go from there.

Jeff C.
1970 280SL 4-speed

[ja17]

Hello Ed,
Start with the cheap and simple things first. Check the fuses. Find the one for the fuel guage and twist it in case it lost contact.

Joe Alexander
Blacklick, Ohio

[Ed Fisher]

Good morning. Thank you for the replies to my questions Jeff and Joe.  I have managed to fix both problems.  

Problem #1.  The dead fuel gauge turned out to be missing/broken solder to one of the pins in one of the big, under-dash connectors.  Apparently, taking them off while troubleshooting the turn signals was enough to break what little connection there was.  I got lucky, when troubleshooting I could move the harness to that connector slightly and see the fuel gauge come and go.  Fresh solder to the wire/pin and the fuel gauge is working again nicely.  

Problem #2.  The new flasher units will work in the Pagodas.  Ron (RBurg) was spot on with his recommendation, which he obtained from Gernold.  The socket that accepts the flasher relay can be taken apart by loosening the three slotted screws.  There are 3 female pins in the socket.  Two adjacent pins and one lone pin.  It is the lone female pin that must be moved to the empty hole next to it and that is all there is to it.  There is no soldering/crimping/rewiring needed.  Just move the pin and button the socket back up.  Since the other relay is NLA, it is nice to fit the modern flasher relay with its nice even switching times.  It was an easy fix.