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MG Midget and Sprite Technical - electric fan/horn wireing

I have a conversions, one of the old ones now.1974 US car with Datsun A15 engine & 5 speed. People have long moved on from that one I think. Point is, I have an electric fan.

The problem.

What I've been thinking is a loose connection in the electric fan/horn circut, now has me more confuesd than before. I've looked and tugged and prodded everything in the dashboard. If it's loose, it should have come looser. Then, afte too many hours, for unknown reason the fan runs. When the fan does manage to run, pushing the horn button can starve the circut into opening up. So no fan and no horn. But then it's all OK.... for the moment. Horn draws some juice as it is an air horn with it's own compressor.

Electric fan runs off the unused switch in the wiper switch. Pull back to turn on, forward to trun off. Also have the amber light in the circut to remind me when the fan is running. Can't remember what that light was originally for.

Recently had a speedometer shop try to fit up a cable to the Datsun tranny. He had is hands in there and knocked some things loose/failed to reconnect some ground wires. May or may not be related to the problem. After all my prodding and tugging, I'm thinking it's not.

I will admit that my wireing is mostly original. Not pretty. It's a forever porject car. Someday it will all be done right.

Hope somebody out there has seen this before.

Thanx.




Don Anderson

Nice car, nice weather. I hate you!
Q is, where does the power come from? Normally the horn is from the fusebox browN > Purple, off the P side. If the fan is running off that fuse, then a bad connection at the fusebox is prime suspect. Dirty fuse contacts or bad riveted connection in the box.
The extra switch in the wiper is for overdrive on (probably) MGB, so I think you have a changed switch. I hope the fan is working off a relay, because that wiper switch is not designed for that kind of load.
I would replace the fusebox with a modern blade fuse type or two, and run both the fan and horn off relays separately fused. Of course, I'd also rework it so the headlamps were on relays with fuses too.

FRM
FR Millmore

or you could perhaps run a seperate fresh new supply from the battery through it's own fuse to a thermo switch, comes with relay, and let the thermostat do the work

something like this http://www.revotec.com/EFC25-38.htm

that way you can take the present switch and light out and remove the old fan wiring off the the horn curcuit

(nice looking car, not sure about those wheels this side of the pond tho')
Nigel Atkins

Thanks for the responses, and the compliments.

Since I first suspected a compromised ground connection behind the dash due to the ones I found left open, my battle last night was focused there. But when it started working with my hands not on anything AND demonstrated horn was also involved, then my suspicion has moved from under the dash.

Yes, the fan is on a relay. I was looking for a factoy relay for the horn as well. Is there one?

Whether I go back with another thermal switch or not, I like haveing the light to tell me the fan is running.

Back to the attack mode in real daylight. Thanx again.
Don Anderson

Sorry I don't know if your model did have a horn relay, one could have been added if not

the US car are a bit more complicated that the UK models

having the horns and fan wired together doesn't sound a great idea to me tho'

>>I like haveing the light to tell me the fan is running<< I'm sure a thermswitch could be wired so that happens, I know it's for reassurance but I'm not sure it's needed as you probably don't have it on your modern car and don't worry or even think about it plus you can hear the fan operating at lower speeds which is when you need it

Even though your car isn't standard a (US) owners handbook would still be very useful to you

good luck

Nigel Atkins

if wired correctly, there should be no downside to using the horn power supply to also supply the fan, as the purple feed to the horns is a fused, +12V source that is always on (ideal for a fan). Just make sure the total current draw does not exceed the wire's size.

That same purple wire, by the way, makes a handy place to connect a battery trickle charger (it avoids having to run any new wires through the engine bay, as that wire is right up front).

Good luck in your search to find the bad connection. Be systematic, and follow each circuit (with a volt meter) all the way from the battery to the switch to the device, to the ground and you are sure to find the fault.

There is nothing as frustrating than a ham-fisted mechanic that messes something else up when trying to fix one thing!



Norm
Norm Kerr

No factory horn relay on US car.
You might want to check Rick Bastedo's thread "78 midget & ignition trouble" on the general board.
Kindred spirits and such!

FRM
FR Millmore

Hunting down to kill the issues,(horn & fan were just a couple of them)I got tired of all the gime on my hands. So I did a pressure wash, knowing that it could make things worse electrically. Well, it didn't. The fuel gauge started working, the turn singnals started working, fan and horn are happy. Rest assured that the rats nest will still get cleaned up. But nice the know that it will be OK. And I also got to see the source of the grime. One valve cover screw has apparently dimpled it's hole.

So aside from the rats nest that will go away, here are the remaining items.

Tach.
My Hanes manual shows a white wire from the tach to the coil (on one diagram it's going to the positive side) The it changes to a white with black strip from coil to distrubtor. What I have is a white/black all the way. And there is a second connector on the tach with no wire. Is that supposed to get 12 volts?

Fuel gauge.
Half tank and above shows a full tank. Half tank and below starts to drop until what is indicated as half tank is actually empty. I remember something about an adjustment pot on the firewall. 2 similar looking.... things... next to each other on the firewall with what looks like the same green/brown wires, and neither has adjuster pots.

Where to find a better diagram? It only takes one inaccuracy to make my head implode.

Thx
Don Anderson

Hi Don,

glad to hear that you are making progress.

Here is a link to the diagram for a US spec 1974. Unfortunately, 1974 is the "worst" year for complicated wiring diagrams because of the seat belt interlock that one year.

http://www.spridget-tech.com/service_manual/Appendix.pdf

see page 377.

One nice thing is that many of the other parts of the car not related to that interlock system are the same on previous year cars, so you can look at their simpler diagrams from those years to get familiar with things. Doing this helps make it less overwhelming at first.


For your tach question: your Haynes manual has a typo. The wire from the coil to your tach SHOULD be white / black!

The white wire that supplies the other side of the coil (+) is +12V when the key is "on".


For your fuel gage question: there is an adjustment on the back of the fuel gage. But from your description, it could be that the wrong year sender unit was installed in your fuel tank. I had that problem and simply painted a new "empty" mark on my gage glass until I got around to taking the tank out and fixing it.

here is a link to some articles that show the inner workings of the fuel gage system (these are written for the MGA, but almost all of it applies equally).

http://mgaguru.com/mgtech/fuel/fuel.htm


hope this helps,
Norm
Norm Kerr

second thought about the fuel gage: could a bad voltage stabilizer cause symptoms like you describe?

The voltage stabilizer is a small metal "box" mounted behind the dash board, and you mentioned it in your post above, there are two similar "things" nearby each other, back there. One is the flasher for the turn signals and the other is this thing for the fuel gage. You can tell them apart by the color of the wires going into them:

voltage stabilizer: light green / green, and green

turn signal flasher: light green / brown, and green

the other way to be sure you've got the right one is to unplug one wire of the one you think it is, and check to see if your turn signals still work!

If you want, you can get another voltage stabilizer and try it to see if it makes any difference. This would be, by far, the simplest solution, and if your gage was working correctly up until just recently, then it would be my first guess (the other possibilities, a gage out of adjustment, or a wrongly installed sender unit, are not likely to change suddenly).


Norm
Norm Kerr

First thing that can to my mind was voltage stabiliser - you can replace it with modern versions see -

http://classicstabilizers.webs.com/information.htm

make 1 - (as above)
http://cgi.ebay.co.uk/Semiconductor-Voltage-Stabilizer-MG-Midget-MGB-MGC-/280648813149?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4157f90a5d

make 2 –
http://cgi.ebay.co.uk/SOLID-STATE-VOLTAGE-STABILIZER-GT6-Spitfire-Stag-2500-/130502035934?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item1e628709de
Nigel Atkins

This is mega giga help guys. Thanx.

Remaining question one the tach. One spade connection with nothing on it. Right next to the bullet type connector for the white/black wire. This connection appears to be isolated from the ground and the w/b conneotor. I see on the diagram a green wire going to the emergency flasher. Am I seeing it right, and is this supposed to become a hot to the tach?

By the way, I'm not in Indonesia now. Tried to change that to California/Mexico, but it didn't take.
Don Anderson

You are correct, there should be a green wire attached.

(green is fused, switched power, and is also used to power the instrument and turn signal lighting)

Norm
Norm Kerr

OK,Thanks. I'll put it all together tomorrow... I hope.
Don Anderson

update

Got everything working. Thanx a mill.

Tucked all the harness/rats nest up behind the dash, fuel gauge and turn signals quit. Not much left to quit now is there?

Key switch is bad. Whatever else will be revealed as I muddle thru. Starting with the key switch, since the thing unplugs, best to just replace everything between key and plug. There are mechanical bits in there that seem to make the mechanism reluctant to give me back my key sometimes.

On the key switch harness, there is one lone, loose purple wire that has a male spade connector on it. Can't find a home for it. All the other wires coming out of the plug are soldered to the key switch. Any ideas?
Don Anderson

Nevermind. I see it now (purple wire). Ignition/door alarm switch. Gotta have one of those. One thing about removing devices. Remember to take their leads back to a nub if they are never going to be used again. Less head scratching later.
Don Anderson

Well done

>>mechanism reluctant to give me back my key sometimes.<< mine’s like that sometimes I think it’s the ant-theft locking device on my mine

fuel gauge might just be earth wire loose/bad connection (?)

Your cars are a bit more complicated than UK cars, mine has female Lucar connectors on the wires to switch

I think you should start at the battery and work your way to the fuse box and then each individual circuit and components one at a time checking connections and wiring are clean, secure, protected and going to the right places

I’d also suggest taking your time and have plenty of tea or beer breaks if you’re getting frustrated

Sounds like a previous owner has used your wiring for knitting practice so any wiring take as possibly incorrect check it with the original wiring diagram
Nigel Atkins

Key switch seperated from key mechanism. I can see the potential for the problem to be in the mechanism rather than the switch. Anybody else chase the worng problem here before?

As far as the PO's wireing goes, what I'm calling rats nest, Lucas called harnesses. Much of the debris is from my removing devices that were required when it was a new US car in 1974. I really should have cut wires back to the nub. But I didn't "just in case". I'll be correcting that this time. But the famous Lucas bullet connectors are just living up to their reputation.

So key switch. What yer experience when they go bad? Switch or mechanism?

Don Anderson

Ign/steering lock is completely separate from the switch, except that the switch is driven off the lock. Trouble with the key/lock is the result of bits of die casting floating around in the works, take it apart and clean and lube everything. Check that the key correctly retracts the tumblers while it is apart, new key if needed. Replacement ones are far worse than worn originals, frequently take a lot of work with jeweler's files and such to make them work at all, so try to clean up the old one. Lot of info in the MGB archives about this.


From previously posted by me info:
"I have just completed a major cleanup of a 73 MGB with all sorts of electrical troubles involving bad connectors. This car has had no proper maintenance in its life; everything worked, but not well. With one exception, EVERY double connector sleeve on this car was broken! Furthermore, after I used up all my new ones, I went to my extensive good used supply, and found that 90% of those broke when I checked them. There is a well known tendency for hard temper brass to crack as a result of age, 30 years appears to be the critical age! I formerly found 1 or 2 bad ones when going over a car. I am now doing a 74 Midget, and it looks like the same story as the B.
The single sleeve connectors on the same cars are much better, I’ve only found a few bad ones. This reinforces the idea that the failures are aggravated by heat.
The Lucas sleeve connectors are pretty good until they get this old, and if you change them for something else, you make subsequent service a nuisance. They should be very tight if they are good; if assembled with new sleeves and OxGard they should last another 30 years or more.
The soldered on bullet connectors only give trouble when they are corroded or torn off because they are seized; OxGard prevents both. It can be difficult to solder new ends on old wire; if possible when reworking a harness, preserve the existing end connectors and splice/solder the wire several inches from the end; insulate with shrink tubing."

FRM
FR Millmore

FRM post plus as FRM points out Lucas are not that bad - your car is 36 years old so they've not done bad

I'm not sure just >>cut wires back to the nub<< best to leave them and terninate them all correctly with some sort of insulted end caps, unless that's what you meant

My only experience, on another car, was ignition switch gone faulty probably because (as possibly with your case) of wiring problems elsewhere

If a lot of the wiring or connections are suspect then best you don't look for for quick solutions better that you take your time and go through the whole lot, it could save more time, potential and actual problems later and give you confidence in the wiring

Nigel Atkins

Yes, the key switch is seperate, but driven off of the lock. Hence the question. Is the lock driving the switch far enough, or is it too worn to do the job?

I can see the contacts make and break instantly with the ignition warning lamp, and both lock and switch are very suspect. Takes a little wiggleing of the key, let go and the circut can open. Going well past (to start)does nothing to make a better contact. But then, for no easialy visable reason it can all work just fine.

Removing the key lock is not so clear a process on the Haynes manual. I'm not too excited to do that.

Last week everything was working and I was driving the car. I went to tuck the harness up a little better under the dash and.... This week the steering wheel is off and the dashoard is pulled back to clean things up. Gauges are all cleaned up and operable. Time to replace ratty switches and clean up/dress wireing.
Don Anderson

This thread was discussed between 26/03/2011 and 02/04/2011

MG Midget and Sprite Technical index

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