I added an aftermarket auxiliary tank to a Dodge van. It came off a Chevy pickup. This used a mechanical fuel pump, so all I needed for that was a valve. Wired the original gauge so I could switch it between tanks. The OEM gauge/tank display stayed correct, but the aftermarket was backwards and out of range. In other words, the aux tank read something like nearly empty when full, and way above full when it was empty. Different makes (and apparently years) use different schemes (like is low resistance full or empty?) and different resistance ranges as well.