Hi unrared
I am (Swiss) German speaking - what does "500 point scoring loop" means ?
The ball hits the target and You get five times hundred points - BUT it does not stop You get another "five times 100 points" and again and again - but always 5 times 100 points ?

You have marked in the picture "switch on the right" - question - when the ball hits on the left: Do You get the same fault ?

IF (if, if) the fault ONLY shows up "on the right": Most likely the playfield switch is no good. In the ipdb-schematics I see two switches mounted parallel - so the 500-Relay gets activated --- when ONLY ONE playfield switch causes the fault - I clue: Must be the playfield switch. Greetings Rolf

Hi unrared
I want for the moment ONLY look at the 500-Relay problem. Here http://mirror2.ipdb.org/files/1072/Williams_1976_Grand_Prix_Manual.pdf on page-32 (ori-30) - the Switch-A on the 500-Relay. This is the (JPG, encircled orange) Self-Hold-Switch. Toggle-off the pin and inspect this switch - OPEN when the relay is not pulling ? A drop of solder fallen at the short stubs with wires soldered-on - a drop of solder - making faulty connection ? short stub bent making faulty contact ?

Maybe the switch --- I believe in: ONE or both of the Playfield-Switches is faulty --- look for wire-color-brown-black / yellow. IF (if) You have mounted new rubbers: You may have bent the switch so it it always closed. Not only at the 500-relay-switch --- also on the playfield switches: Look for drop of solder / bent stub.

question for "troubleshooting Bonus problem": Coil A-22-550 ? Left ? or right ? or both ? Immediately starting or starting when the Outhole-RELAY pulls-in ? Greetings Rolf

P.S.: The Bridge Rectifier and the stuff connected to it: We do not need for the problem "500-Relay".

0Grand-Prix-Work-19 (resized).jpg