MG Car Repair: mgb electrical ground points, manual drawings, starter solenoid

Question
Hi, I have a 77B which I recently installed a new clutch and other parts while I had the engine out. Now my probblem is,the car runs ok but I have several electrical problems especially with gauges. When I blew the horn I noticed that it blew with a viberating sound.Not a steady tone at all. when I checked the #3 fuse my test light flashed consistantly with the horn. Fuse #4 was a steady battery indication. It seems as though it has the same frequency as the fuel pump noise.Could this be a ground problem somewhere on the car. I can't find any ground strap from the engine to the chassis. Do you know of any drawing showing where every ground point on the car is located? Not just the shop manual drawings(I have 2 different ones),but the actual placement on the car.   Thanks

Answer
Hi Cecil,
It does sound like a ground problem or a battery terminal problem and since you had the engine out check the power wire connections on the starter solenoid and battery post connections.
Also the ground strap which as I remember on the 77 was at the engine backing plate to bell housing bolts down close to the bottom. The older MGBs had it at the motor mount.
An easy test if it is a ground problem is to connect a battery jumper cable from the engine to the ground post on the battery and look at your test light again.
Howard