We had a workday north of Baltimore the last week in October, and I was lucky enough to have about five sets of hands helping diagnose my fuel sender issue. What we were able to sort out is as follows:
- My wiring loom up to the bulkhead is not original, but contains original green wiring.
- The ground spade on the sender wasn’t connected (it must have come off at some point after we installed it) but it is now.
- The sender is working properly. We tested it for resistance and it works when we slosh fuel around in the tank.
- The PO put in a grounding wire directly to the frame, which I cleaned up with some sandpaper.
- The wire going up to the bulkhead connector works.
- The bulkhead connector is a mess, and has been screwed with quite a bit.
- Everything behind the dash is a mystery.
The service manual says we’re looking for wire 36-16, which checks out behind the dash but the wire going from the sender through the loom looks like 11. Additionally, the 11 loop (the one which appears to ground on a stud welded to the backside of the dashboard) was loose, so I reconnected that.
While I was there, I bought a Thermoquad from Jason H. for tinkering (it’s the one on the left; the one on the right will get rebuilt as my spare).
MIke Carey says:
i hit all my grounds with dialectic grease just for extra insurance/conductivity.
if you want my old thermoquad let me know. :-)
Phil says:
Hi Bill,
If your other gauges are ok, I would do a physical inspection of the wiring, even if it passes tests with an ohmmeter. If the copper is darkened or brittle, it is probably failing under service conditions. You might be better off bypassing the factory harness entirely rather than trying to repair it. My ’75 developed electrical bugs that drove me nuts because the wiring was just good enough to fool the diagnostics. I learned to just replace the whole damned circuit when something started misbehaving.
If any of your other gauges are misbehaving at all, check the gauge voltage regulator (sometimes called a “vibrator”). I think it lives behind the oil pressure gauge in Scout IIs. The originals are often mechanical, and are high-failure items.