4107 Fuel gauge

[Bill Gerrie]

Does anyone have a wiring diagram of the 4107 fuel gauge and sender? It appears to be different them a normal float with one sender wire.

[chessie4905]

How many terminals on your sender?

[Bill Gerrie]

As of right now I can't get to the sender but the gauge has 3 terminals but only 2 used. It appears as if the ground might be coming from the sender to give a reading. A white block mounted on the back  of the gauge as well. As it is listed in the manual as optional equipment there is no wiring diagram in the book.

[chessie4905]

On the 4108,4905 the sending unit only uses one wire, a resistance to ground connection to gauge. Check aftermarket gauge sender info,ie. Auto Meter, Stewart Warner, etc.

[Bill Gerrie]

Chessie
Do you have any idea of the ohms of the sending unit?

[chessie4905]

I just went out and checked on the gage I replaced. It is stamped 90 ohms. I believe GM used that resistance on all their gages, cars, trucks, buses, and coaches. The gage or sending unit is not listed in the coach parts book, as it was optional equipment. It would be in a SEO supplement book which I would love having g a copy, but I don't know if any are available.
The fuel gage received a switched 24 volts. The other terminal on gage connected a wire going to the fuel sender in tank. There also was an option to have an additional gage by the fuel filler neck. The switched power to that gage was activated by a spring loaded or momentary on-off switch. I would like to see a picture of this gage to see how it was mounted.
I used to have a 1948 ACF Brill IC41 that had this option.
BTW, the coaches had two tank sizes, standard was 145 gallons, optional was 165.The tanks were identical other than the larger one was about 18 inches longer. It reached completely to the driver's side while the smaller one left a recess there. Both tanks use the same gage and sending unit.

[Bill Gerrie]

Thanks chessie
That is what I needed to know. First step is to replace the gauge as it appears dead and a last resort is the sender.

[richard5933]

Funny... I just picked up our 4108a and had to ask where the gauge was. Answer was that there wasn't a need. Tank holds 165 gallons. At 8-10 mpg, that's one heck of a range. I know that this doesn't answer the question, but I though it would add a little different perspective.

Richard

Richard
1974 GMC P8M4108A-125 (Current bus)
1964 GM PD4106-2412 (totalled Sept 2017)
Located in beautiful Wisconsin
KD9GRB

[Bill Gerrie]

Richard
They were a special equipment option. Just nice to know when you are about to run out of fuel in the middle of nowhere.