I'm hoping for some wisdom from anyone who knows more than me about vehicle electrics... and believe me, that's pretty much everyone 
So with this admission in mind, please work from the premise it's not possible to patronise me too much 
Right, specifically, I have a problem with the electric radiator fan conversion on my FB RX-7. The car originally came with a viscous fan, which has now been deleted. I bought a Kenlowe full kit to replace it because it seemed an all-in-one solution, but with one thing or another it's been an endless PITA. First off, the little control box/thermostat thing blew up almost as soon as it was installed, so we fitted a replacement. This seemed to work fine for a few months, but the car overheated a couple of times because the fan would intermittently stop running and this was traced to what appeared to be a faulty relay... if you pushed down on the top of the relay it would fire, but as soon as pressure was released on the plastic case, it cut out again. I replaced the relay, and it worked OK for a few weeks before the same problem repeated itself. Then the new control box fried itself; not in a "it went bang" way like the first one, but more annoyingly in an intermittent way.
Soooooo, we sacked off the entire Kenlowe control box/temperature probe setup and fitted a solid-state thermo-switch into the waterpump housing. It's from a Nissan Micra, oddly, simply because it had the correct m16x1.5 thread and the right temperature range; on at 90 and off at 85 degrees. This seemed to work fine, except now the fuse blows instead. Not all the time, annoyingly. Only when it gets hot (lol). It's a 25 amp fuse, and I tentatively tried a 30 amp but that blew as well. The irritating thing is, if you bridge the two thermo-switch wires together, the fan will come on and run happily, seemingly as many times as you want. It's only when in the stress situation of long-term stop-start traffic jams (the M25 is a good one) that at some point the fuse blows and the only way I can tell is that the temperature gauge just keeps climbing
so, if anyone's still reading, the wiring goes like this;
switched live to relay 85 terminal (from ignition feed to coils)
+12v direct feed to relay 30 terminal from battery terminal
thermo-switch goes to earth and to the relay 86 terminal
relay terminal 87 goes to the fan motor, and the fan to earth
this leaves me a few variables to ask about;
The relay has the same ratings as the one that came with the fan kit. I kinda understand (a bit) how a relay works; it basically throws when it detects demand so that it feeds battery rather than stepped-down circuit voltage to whatever it's connected to (i.e. the fan). But what effect does the amperage rating on the relay have? This one is a 40 amp, which seems quite rare compared to the common-as-muck 30 amp ones. Surely its purpose is to regulate power, not current, so why the different amp ratings? Surely the fan will draw as much current as it needs irrespective of what the relay "thinks" it should? Is this the problem, should I drop the amp rating on the relay?
Is it the fan that's the problem? Is it a case that when it's all hot, it sooner or later draws a sudden current spike at switch-on point, before the relay can actuate and this blows the fuse? If so, how can you avoid this? Or is it simply faulty? Note that I've never got it to blow the fuse when cold, no matter how many times I fired it
Because the original Kenlowe probe is no longer in the circuit, but the gubbins (fuse, relay and wiring) are all still in the location that it was originally mounted in, there is a really long run of wiring involved... basically it ruins from top/middle of the engine where the waterpump/thermoswitch is, across to the nearside where the battery mounts, then down in front of the radiator along the crossmember to end up on the offside radiator mount. Will all this length of wire have an adverse effect? Also, presumably you want the fuse as near as possible to the battery, also?
Is the thermo-switch the problem? It runs without even a relay on the Micra circuit, far as I can tell, so it's obviously intended to switch some manly voltage... but is this too much for my setup?
Could it be as obvious as am intermittent wiring fault... a chafed bit of insulation or dry joint in a connector somewhere that only shorts when heat and vibration are introduced?
Sorry for the million stupid questions, but I'm running out of ideas with my feeble knowledge of electrics. I've decided to replace the entire wiring setup and try to make it a bit more... well, organised and shorter... in the hope changing the cheap stuff is a better start than the expensive stuff (i.e. the fan) but it'd be annoying to do all that faffing about only to keep the same problem.
Help!
So with this admission in mind, please work from the premise it's not possible to patronise me too much 
Right, specifically, I have a problem with the electric radiator fan conversion on my FB RX-7. The car originally came with a viscous fan, which has now been deleted. I bought a Kenlowe full kit to replace it because it seemed an all-in-one solution, but with one thing or another it's been an endless PITA. First off, the little control box/thermostat thing blew up almost as soon as it was installed, so we fitted a replacement. This seemed to work fine for a few months, but the car overheated a couple of times because the fan would intermittently stop running and this was traced to what appeared to be a faulty relay... if you pushed down on the top of the relay it would fire, but as soon as pressure was released on the plastic case, it cut out again. I replaced the relay, and it worked OK for a few weeks before the same problem repeated itself. Then the new control box fried itself; not in a "it went bang" way like the first one, but more annoyingly in an intermittent way.
Soooooo, we sacked off the entire Kenlowe control box/temperature probe setup and fitted a solid-state thermo-switch into the waterpump housing. It's from a Nissan Micra, oddly, simply because it had the correct m16x1.5 thread and the right temperature range; on at 90 and off at 85 degrees. This seemed to work fine, except now the fuse blows instead. Not all the time, annoyingly. Only when it gets hot (lol). It's a 25 amp fuse, and I tentatively tried a 30 amp but that blew as well. The irritating thing is, if you bridge the two thermo-switch wires together, the fan will come on and run happily, seemingly as many times as you want. It's only when in the stress situation of long-term stop-start traffic jams (the M25 is a good one) that at some point the fuse blows and the only way I can tell is that the temperature gauge just keeps climbing
so, if anyone's still reading, the wiring goes like this;
switched live to relay 85 terminal (from ignition feed to coils)
+12v direct feed to relay 30 terminal from battery terminal
thermo-switch goes to earth and to the relay 86 terminal
relay terminal 87 goes to the fan motor, and the fan to earth
this leaves me a few variables to ask about;
The relay has the same ratings as the one that came with the fan kit. I kinda understand (a bit) how a relay works; it basically throws when it detects demand so that it feeds battery rather than stepped-down circuit voltage to whatever it's connected to (i.e. the fan). But what effect does the amperage rating on the relay have? This one is a 40 amp, which seems quite rare compared to the common-as-muck 30 amp ones. Surely its purpose is to regulate power, not current, so why the different amp ratings? Surely the fan will draw as much current as it needs irrespective of what the relay "thinks" it should? Is this the problem, should I drop the amp rating on the relay?
Is it the fan that's the problem? Is it a case that when it's all hot, it sooner or later draws a sudden current spike at switch-on point, before the relay can actuate and this blows the fuse? If so, how can you avoid this? Or is it simply faulty? Note that I've never got it to blow the fuse when cold, no matter how many times I fired it
Because the original Kenlowe probe is no longer in the circuit, but the gubbins (fuse, relay and wiring) are all still in the location that it was originally mounted in, there is a really long run of wiring involved... basically it ruins from top/middle of the engine where the waterpump/thermoswitch is, across to the nearside where the battery mounts, then down in front of the radiator along the crossmember to end up on the offside radiator mount. Will all this length of wire have an adverse effect? Also, presumably you want the fuse as near as possible to the battery, also?
Is the thermo-switch the problem? It runs without even a relay on the Micra circuit, far as I can tell, so it's obviously intended to switch some manly voltage... but is this too much for my setup?
Could it be as obvious as am intermittent wiring fault... a chafed bit of insulation or dry joint in a connector somewhere that only shorts when heat and vibration are introduced?
Sorry for the million stupid questions, but I'm running out of ideas with my feeble knowledge of electrics. I've decided to replace the entire wiring setup and try to make it a bit more... well, organised and shorter... in the hope changing the cheap stuff is a better start than the expensive stuff (i.e. the fan) but it'd be annoying to do all that faffing about only to keep the same problem.
Help!
It's OK, I managed to not get any blood on the wife's best carpet on my way to the bathroom, and my left ring finger was never my favourite one anyway 
. Pardon my French. Still gonna re-do all the wiring anyway, partly cos I've already stripped it all out and found some bits I'm not impressed with (like, the fuse is the wrong side of the relay, and overall the wiring stretches out longer than the actual car