do all relays need to be diode isolated?

Cool thanks, hey out of curiosity what is the reason it is preferred in the location you suggest?

Well if you think about it logically, since pin 30 is the pin where current is introduced to the circuit it would be wisest to fuse it here as close to the source as possible as it minimises the risk of possible grounding  and not having a fuse to protect the circuit, if you were to fuse at pin 87 and the wiring grounded out from the side of pin thirty? Catch the drift? I thin you're covered since you already fused within 12 inches of the battery, but hey you could go closer, commit your way to jehovah and he will act in your behalf. psalms 37:5

European Telecom rules mandate the fuse 4" (10cm) from the source; battery, fuse box, ignition, etc.

Interesting. But I assume that does not apply to BIG telecoms batteries... (Australia's telecoms regulating body Austel once mandated fusing for all telecoms-exchange batteries. That requirement was later withdrawn. Bu distance (from source) specs vary greatly with the authority and the application.

MOBILE comms Peter. For years, Orange insisted on both POS (fused) and NEG going to the battery. I used to argue that the spurs on say Mercedes under front passenger floor measured out at 12.6V+ to the nearest ground point but they wouldn't take the chance. Even made us fuse the head unit mute line with a 1amp fuse, a bit like placing a 500amp fuse on a domestic cooker line then wondering why your house just burnt down.

I just saw the "European Telecom". I thought the ignition was strange, but assumed that was the result of the fusing (ha ha), though I wonder what ignition they use in exchanges anyhow aside from diesels. Mobiles tend to be less centralised and use less power than landlines. They also use 24V and -ve earth/ground as opposed to +ve earth/ground in traditional 48V telephony systems. That could account for Orange's philosophy depending on what the common connection is between systems. Though normally the grounds would be commoned, that means a 48+24 = 72VDC system which exceeds LV DC requirements (ie - HV DC Licenses etc are required...) Ah - Mobile as in mobile - not mobiles (cells, GSM etc). Does that mean all vehicles with mobile comms must have fuses within 10cm of the battery? That's put most cars of the road here. (Some might be physically close to 10cm, but not electrically.) I'll have to see what fuse my mobile has (if any), though that will be within 10cm. Or maybe one day I'll read those Rules instead.... A 1A mute fuse - yeah, it's a bit like fusing a voltmeter....

There's a whole British Standard and because the rest of Europe is too lazy to test car products (Thatcham in Berkshire, UK), any British Standard becomes the de facto Euro Standard, and to some extent Oz and NZ.

I think it's called MPT 1900, Google it. It goes into all the obvious bits like mandatory solder joints etc.