Wiring for Sport-Comp AM3316 Fuel Gauge

Discussion in 'Mech Tech' started by mgbman, Jun 26, 2019.

  1. On my son's T25 the original fuel gauge has not worked for months and we are thinking of replacing with a Sport-Comp AM3316 gauge from VW Heritage.

    This gauge is rated at 33 to 240 ohms range and matches the VDO tank sender. I have a spare nearly new one and the multimeter shows its good and in range.

    We need to drop the tank anyway, which is centre mounted and easy to get at, as the repro balance pipe is too short and popped out the tank, and the earth wire from sender to chassis is crusty as shown on the endoscope.

    Accessing the original guage wiring behind the dash is a pain and the old pcb ribbon circuit is fragile and prone to breaking just by looking at it and a new one is £250 so understandably my son wants to leave well alone.

    As the tank is coming out we can do any wiring needed and presumably the new gauge is simpler and works at 12v.
  2. any help from @Bigherb and others would be welcome.
  3. The tank sender resistances are different for early and late instruments. He's got an early one hasn't he?
  4. thanks for your reply. yes its a 1980 Devon air cooled.
  5. Early senders are 50-55 ohms full. Can't find my note book at the moment but I think I work on 160 ohms for 10l reserve. There is a 4 way connector above the fuse box that the purple/black sender cable goes through.
    Personaly I would try to get the original gauge working.
    Not much to it really
    Check you have 10V at the voltage regulator output to the gauge (ignition switched on), Then check the voltage at the sender terminal it should be around 3v with a full tank, rising to around 9V empty or somewhere in between depending on how much fuel is in the tank.
    Dscn1280 640 Marked.jpg

    1-9 T3 80-82 Fuel Gauge.jpg
    Valveandy, mgbman and paradox like this.
  6. that's very helpful. thanks. I agree about sticking with the original gauge which was working fine. about 18 months ago my son got his mate who has a vw garage and very experienced in splits, bays and t25's. to do some jobs on the van including fitting new fuel tank, all pipes, sender and so on. all worked fine until started to work then not work and now doesn't work at all. The only item reused was the wiring to the new sender.

    we used an endoscope to view across the top of the tank and sender and wiring. all in place but we saw a wire going to the chassis with a very crusty connection, which we thought was the sender earth wire?

    Is it that brown wire in the diagram from sender to front crossmember left?
  7. Yes it is, I always remake them as a matter of course.
    mgbman likes this.
  8. yes that's the one. ours is bad and maybe the cause of the problem.

    we need to lower the tank soon to sort out the balance pipe which is a repro part and looks about 2 inches short so its taut and pops out of the nearside tank grommet, we have a length of 7.9mm fuel hose which we could use to replace that plastic balance pipe. we will make a new wiring connection as you did.

    before all that we will take your advice and test the volts at the blue ribbon end. we have removed the instruments binnacle and don't really want to remove anything else.
  9. You don't have to take the instruments off, just remove the cover and peer in the through the windscreen to see the connections.
    mgbman likes this.
  10. Hi @Bigherb thanks for the help. Well we checked out the T25 fuel gauge today as per your instructions.

    We cleaned up those terminals shown in your photo and put the meter on them one at a time, ignition on and this is what we got,

    Voltage Regulator 10.45 Volts

    Sender terminal 10.45 Volts

    So both readings the same, tank about quarter full, gauge not registering anything.

    Where do we go from here?
  11. There is no circuit through the sender, check wiring/connections, purple/black wire goes from instruments plug via four pin connector above fuse box there is the easiest place to intercept the sender wire and earth it, the gauge should go to full. If it does the sender or sender earth wiring is at fault.
  12. wonderful, many thanks. we will try that next weekend and post results.

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