Sender wire should come up to the guage via lower driver seat, up through left cowl. Don't think any fuel guage issues run through the firewall however it is an area that deserves attention. I just spent 4 whole days and about $200 i new parts trying to figure my gauge issue. Would work well if VL was not grounded. Once the cluster was placed into dash. Would rise slightly and go back down. After testing ohms, grounds, etc. I ordered the MeterMatch product. Hasn't arrived yet but we'll see.