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MG Midget and Sprite Technical - Frogeye wiring confusion

Help! The car is a Healey Frogeye (Isle of Wight) which uses the Mk1 sprite two-fuse system. My Kenlowe fan stopped running the other day, which in 30 degree heat was a problem. It was fine when I parked, but when I returned to car 10 minutes later and turned on the ignition, no fan. In this weather I keep it on all the time.
I assumed that the 20amp fuse had blown and I could just replace it when I got home. Indeed it had blown (or rather the end cap had become detached) but replacing it made no difference. This is the A1-A2 fuse which protects items such as horn and lights which function whether or not the ignition is on. So the fuse is in (only had a 35amp, but thought it fine just to test the system).
I can connect the fan up direct to the battery and it whirrs away beautifully. So, the fan, heater blower and horn do not work with the new fuse - but the lights do. I thought that these were on the same circuit.
Any ideas what might have happened? There are no scorched wires anywhere.
I hold up my hands to being useless with electrics. It's not, er, my field. I do have a multimeter somewhere but no idea what to do with all the dials, probes and switches. But I do have wire and crocodile clips to bypass bits and pieces.
Any suggestions gratefully received.
C Whiting

Ah. A clue. I have just found that one of the wires from the heater blower is hanging loose. There is a black one coming from the loom to the blower, and this blue one which is unattached and has no spade or bullet, so I assume it should be earthed (car is negative earth). But I tried touching it on battery terminal (Healey Frogs are not metal!) and nothing. Must be a link though, surely? If the heater is part of the circuit, might that stop the Kenlowe, or is a separate circuit. Note: The blower used in IOWs is not standard Frog, but was swiped, I believe, from a speedboat. Tried to upload a photo but file too large. And it only shows my fingers and a bit of blue wire in the engine bay.
C Whiting

Firstly, the lights weren’t fused, originally.

The black wire coming out of the loom to the heater would, I suspect, be the earth. The original heater wouldn’t have had a blue wire. Power to the heater blower would be from a green wire with a coloured trace. I haven’t got access to a wiring diagram at the moment, but I think it may be yellow, from memory.

The fact that the heater blower is disconnected shouldn’t affect the cooling fan, unless you’ve got some weird wiring.

You really need to check that you have 12v at both sides of the fuse. If only on one side, the fuse has blown, or a bad connection/high resistance. If neither side, the power is being lost somewhere else upstream.
Dave O'Neill 2

That is helpful - I assumed (wrongly) that the lights were fused. It is also helpful to know that the heater blower being disconnected should not affect the Kenlowe fan. I need to find a way to see if I do have 12v at either side of fuse. I have a multimeter but it may as well be marked in Swahili.
C Whiting

If, because of the fibreglass body, the fan and heater share a common earth wire, then if the heater earth was disconnected, then the kenlow would not work either.
GuyW

It seems that it's the live that's loose off the heater, and they do not share an earth. Much scratching of heads at East Kent MASC meet on Sunday but it's looking like it may be a switch issue. I am about to contact the club expert in auto electrics and will let people know what the result is. Many thanks for the suggestions.
C Whiting

Right. Off on Thursday (with Kenlowe wired direct to battery) to see Steve, the Kent MASC electrics expert, who will no doubt work out what is going on, or rather not going on. Will report back with results.
C Whiting

There must be an open circuit somewhere between the fuse and the heater/ fan/ horn which seem to be fed with a common link.
Bill Bretherton

Or there's more than one fault or point of fault.

Was the Kenlowe a factory fit or a PO add in, if later then it's wiring might be non-conventional.
Nigel Atkins

Right. Really grateful to Steve, a Kent MASC member who just happens to be an auto-electrician. Took the car round to him this afternoon and off he went with his test bulb and deep knowledge of what he describes as an extremely simple two-fuse system. Yes indeed, there was a series of coincidences (Nigel) which gave the impression that the pre-ignition part of the circuit was dead, ie the blower and horn were not working. He quickly established that there was 12 volts coming in to both sides of both fuses. The blower wasn't working because of a stray wire wrongly connected when the engine was put back in by the builder and the horn wasn't working because the brass strip in the push had slipped/bent slightly at some stage. But the main issue was that the fuse box is getting a little tired, and although there was current at both ends, for some reason, possibly heat at some stage, the brass fuse holders on the pre-ignition circuit didn't have the grip they should. I'll be looking for new two-fuse box but in the meantime, it's all up and running as it should. Many thanks to everyone for their help and suggestions - much appreciated.
C Whiting

Well done on sorting it.

Whilst all electric wires, leads, switches and connections want to be in good condition and all clean, secure and protected often the fusebox is forgotten about with the connections and underside getting dirty and the connections getting loose, even the fuses can get dirty.

Cleaning, making secure and protecting all connections from the battery posts through each joint/connection to the end items, including all earths, can make a noticeable or big difference especially to items like the starter and lights. A chain as strong as it's weakest link type thing.

I don't know about the two fuse fusebox but be careful about the quality of new parts.

Whether it's original or not I'd always have a cover on a fusebox, I don't even like the thought of the spare exposed external spade connectors on the (4)fusebox.
Nigel Atkins

During the recent re-commissioning of my B, I had all sorts of problems caused by oxidisation in the fusebox. I boiled it in a citric acid solution for 20 minutes, then washed it off and all was well when refitted.
Dave O'Neill 2

For various reasons I have replaced the twin fuse fusebox in my MGA with the Lucas SF4 four fuse box. It mounts with the same mounting holes, takes the same fuses and also has a cover. The the extra fuses are used to fuse the lighting circuit and other accessories.

As the MGA is fundamentally the same schematic as the Frogeye, this may be an option for you too.

If you want a good original two-fuse block, drop me an email
Dominic Clancy

here's a picture

Dominic Clancy

Thanks for all that - there seem to be two versions of the Lucas two-fuse box, one costing about twice as much as the other. I think I'll be best off forking out the extra tenner for what appears to be better built. Although that SF4 does look interesting...
C Whiting

This thread was discussed between 09/08/2018 and 27/08/2018

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