Date registered: Jan 2006
Vehicle: 73 280SE 4.5, 71 300SEL, 03 BMW Z4, 72 Fiat 850, 80 Triumph TR7, 85 Porsche 911
Location: DC Area
Mentioned: 1 Post(s)
Quoted: 95 Post(s)
I had a similar issue recently. It turned out to be a bad neutral safety switch. I discovered this to be the problem by turning the key to the "crank the starter" position and running the gear shift from park to first, back to park. The starter would crank when the contacts in the neutral safety switch connected in the right way.
Tell me, do the backup lights work/function normally?
I ended up taking mine off and cleaning the guts up, but there are ways of bypassing the switch if you think it warrants a try ...
If your accessories work but without power to the fuse block, you have other challenges to overcome that don't involve relays. For the sake of doing it, pull off the ground straps that connect the engine to the chassis, clean them on both ends and cinch back down (I have a '72 Fiat that wouldn't start after I replaced the engine, and it turned out to be a ground strap that I hadn't put back yet).
Poor grounds are a common issue with these old beasts, and one of the easier ones to locate/fix. Do the same with the battery-to-chassis cable. Take it off the body, clean the mating surfaces, and replace.
You successfully jumping the starter tells me the starter is good but the starting circuit is bad. If it's not the neutral safety switch, it's the ignition, or associated wiring.