The grounds inside the front fender serve to ground items that may not have a mechanical ground on their own, they also help tie the car together - BUT they are not an end all to ground problems.

My '90 744 stalled when I turned the high beams on! I found a lot more grounds than I thought there were.

For instance, the power stage gets some ground through its attachment to the fender and the starter gets some of its ground through the ground cable to the battery and through at least two straps that connect the engine to the body and chassis, I also found that there are also some grounds associated with the mount for the anti-lock brakes that can effect the ignition.

ANY item that only has one wire - a power wire - gets its ground through some mechanical connection to the body or to the engine.

You need to look at just how each item could be grounded.

It would be by a dedicated wire that is not an obvious power wire or some mechanical connection to ground.

For example - take the license plate lights on my 544, when they did not work I found -

There is one wire to the light - it gets its ground by - there is a small metal clip on the rubber housing that must ground to the bumperette, the bumperette must ground to the bumper, the bumper must ground to the bumper bracket, which must ground to the body, and lastly the body must ground to the battery.

If any of these connections are bad = no lights.

At your car's age, there may be a lot of connections to check.
--
'96 855R,'64 PV544 driver, '67 P1800 basket case, '72 Yamaha Rd400, '68 Honda 350-4, '12 XC70, the first 5 are mine, heh, heh, 525,000 miles put on 10 bricks James A Sousa