Fuel gauge trouble

New fuel sender arrived today and after learning how to use the continuity function on my multimeter i confirmed that the old one was knackered and new one was reading correctly.

My problem now is that rather than getting no reading at all on the gauge it reads full as soon as the ignition is switched on.

My 90 was originally a 1985 petrol, do you think the problem may be that the new sender is for a diesel?
I would have thought they would be the same gauges and senders?

cheers, Steve

have you fitted the wires the right way round ie feed from gauge to earth

I think so, i have a green positive to one side of the gauge and it earths out on the sender through the green wire with a black trace

easy enough to check which one is live and which sender terminal its fitted to, if it is fitted right wire either has a short or sender does

i have just noticed different part numbers on ebay for gauges that look identical
My gauge is part number PRC3107 whereas the one i'm looking at on ebay is PRC7313.

I wonder if perhaps the sender i have bought is not compatible with my early fuel gauge

it works through a variable resistance if gauge reads full theres no resistance hardly ,rather than an incorrect read, what sender did you fit

Heres the sender:
http://www.ebay.co.uk/itm/370587794689?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

how early is your truck and are you 100% wires are the right way round

Truck is 1985, a very early 90.
I'm pretty sure the wires are all correct, checked and double checked.
I will check the resistance in the wiring though to make sure its not earthing out between the gauge and the sender

it could be but also try swapping wires round, i often test a gauge works by just touching the live from gauge to earth if gauge starts to move up its the sender fault when trouble shooting