Classic/Antique Car Repair: fuel and lights, fuse problems, switch tanks

Question
one of the fuel gauges for my 1984 verden plas  does not work how ever when i switch to the other tank it works fine is there a fuse or relay to look at before i change the sending unit?

when driving the car after about 30 miles when ever you hit the brakes the  brake light comes on like it is indicating a faulty light or circuit but when you stop and check they are all fine turn the key off and restart and all works fine for another 20 or 30 miles.

also where might i accuire a complete head liner for the car.

thanks for any help you may provide
Dave

Answer
Hi Dave,
If one tank reads on the gauge then there are no fuse problems. The problem has to be either the switch, wiring or sending unit in the tank. The tank sending unit is the most likely failed item. However,
First check to see that both return valves and the tank switching valve is operating. The return valves are easy to check. Just open the filler cap on both tanks and with a flashlight look into the filler neck while you hold the flap out of the way. You should see and hear fuel being returned to which ever tank you are running on. But check both tanks when you are using one. This is to see that fuel is being returned to the tank in use and none is being returned to the unused tank. Repeat this on the other tank. If you find a fault check the switching valve in the trunk just to the rear of the spare tire under the long fiber panel and to the left of the fuel pump. Have someone switch tanks while you lay your hand on the valve. You should feel it "Click". If all that is correct than remove the taillight assembly from the side that is not reading on the gauge. (You did not say which that was) check to see if the wires are connected. Two spade connectors. One ground and a sending unit spade. Check the sending unit with a volt meter set on low voltage with the wire disconnected. If you see voltage when the switch is pushed to that tank than that sending unit is bad. Drain that tank by removing the plastic cover on the bottom of the tank and only remove the small inner drain bolt to drain the tank and take the normal fire precautions. Disconnect the battery if the tank unit is to be replaced. If you have a radio that requires a code then make sure you have that code before disconnecting the battery or use one of those small code jumper batteries.
I hope this helps.
On the warning light you may have a brake light failure unit going bad or you may just have resistance in the brake light wiring or even a wrong wattage on one of the bulbs. the failure unit is in the trunk on the fire wall with the Injection ECU behind the carpeted panel.
The headliner material is available at any auto trim shop that does auto head liners. If the fiber board is destroyed or missing your best bet is to contact a local British car specialist or British car club. It is probably a Jag dealer item.
Howard