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MG Midget and Sprite Technical - fuel gauge and wiper motor wiring

Rewiring my '63 midget. Despite going slow and being anal I messed up somewhere and melted some wires. Now I want to be sure I'm putting the correct wires in the correct places.
I need to verify which wire goes to which terminal on both the fuel gauge and the wiper motor.
First, here is the fuel gauge, three spades three wires, GB, B, and G. Disregard how they are pictured. Also the light holder is made from on old ignition warning light so ignore the white and the brown/yellow.
Looking down from the top of it.


J Van Dyke

And the wiper motor.
G, GB, B, which one where?


J Van Dyke

Wiper motor

if I remember it at all the moulded connection with an external vertical tab on it fits the slotted connector on the motor, seen at the top of the moulded pair.
the black one fits the uninsulated earth connector on the casing.
and the other fits the other...

I'll try for a picture this afternoon

You need Haynes for the fuel gauge


A clue to help

Black is earth/ground
green is ignition switched
green/black is ignition fed (green!)- but running to earth (the black trace, so off to the tank sender unit to measure then earth out)

back later if possible with a wiper motor picture
Bill sdgpm

I have Haynes and factory and wiring diagrams but so far I can't ID the terminals on the devices themselves, they're not labeled on the devices. Logic says the unprotected terminal on the wiper motor gets the earth, the harness connections don't have the "tab" on the insulator to fit the slot so can't use that to figure which is G and which is GB. The diagram has E(earth) 1 and 2 but of course they are not labeled that way on the wiper motor itself so, I guess what I need is someone to tell me: top terminal=black, middle terminal(with slot)=GB and bottom terminal(with what looks like a - next to it)=G. Or whatever. Same deal on the fuel gauge. Outboard terminal gets G, inboard gets B and the GB goes to the one next to the G but since those two are physically connected tabs, well. I don't know and am sick of guessing. The fuel gauge is not labeled which terminal is B and which is T and which ground.


J Van Dyke

J(?)

I took a look at mine for you (wiper motor only 'cos all my gauges are in the dash and hidden deep above a console for stereo/CD etc)

Black alone is as I thought the plain earth/ground
Green alone is the slotted socket central terminal
Black wih a green trace is the next insulated (bottom-most on the car) unslotted socket

The picture is as close as I can get to it with the heater box in place but shows fairly well the fitting sequence (black uppermost Green centrally and BlackGreen bottom)

which makes sense (sort of...) in that wiper mootors are wired weirdly to account for the live earh switching that allows the system to park

Green is live IN black always provides an EARTH return and in the case of the black/green this is via the powered PARKING circuit inside [I think]

It seems the numbers would be
EARTH/GROUND none
2 green
3 black/green
onthe motor connection

And on your photograph the slot has the number 2 cast on the connector and the unslotted one has the number 1 cast on it

problem solved, these numbers correspond to the Haynes manual ones exactly

Haynes often gets treated as less than good when it isnt too bad at all

HTH


Bill sdgpm

Holy cow you're right? The terminals are labeled! Couldn't see with the naked eye but can in the picture! Now I feel stupid(er)! So that explains my problem The wiring diagram show E 1 2 but reality is E 2 1 top to bottom.
Lesson is don't use wiring diagrams for the physical location of anything.
Cool, thanks for pointing that out.
Closer inspection of the fuel gauge is next.
J Van Dyke

I'll try to help with the gauge

the earth is NOT for the gauge to operate, that earths at the tank unit.

The earth must be to allow the internal bulb to light up.

That is the BLACK wire.

Fuel gauges (mine at least) have an IN wire and an OUT wire

GREEN will be in from the power source, early cars had live only and later ones have a voltage stabiliser with its output from the "I" terminal via a LIGHT GREEN/GREEN wire.

Your '63 should have an unstabilised voltage (basically as page 197 in Haynes)

The gauge ought to have terminals marked "B" and "T"

"B" receives power from the ignition circuit off the fusebox in a GREEN wire

It then sends the voltage along the "T" outlet to the tank via a GREEN wire with the BLACK trace line that indicates it will earth at the end of its journey, on the tank.

The gauge reads the resistance in the circuit and then indicates how high the float is from the indication it receives as it earths.

The earth is usually apparent as it isn't usually insulated on the gauge body, and is usually offset whilst the two "OPERATING" terminals are usually spaced symmetrically across the gauge, somewhere on these two there should be visible even if only vaguely impressed, the letters "B" and "T"

Even if you get them marked back to front no harm will occur but the gauge wont "turn on", a simple matter of swapping them round ought to get it working again then.

good luck
Bill sdgpm

J

Jwho?
Looking at the picture again of your gauge, it seeems there are two connectors on one terminal and one on another.

I would NOT add a black wire to either of the two together ones, at best you would be liable to blow the fuse every time you turn on the ignition.

As I say above the gauge should be marked "B" and "T"

I would assume (with NO evidence) that the twin connection might be in order for the Green wire to use as a spur if it is needed at some time, this I would expect to be the missing "B" terminal. The other insulated terminal is likely to be the output to the tank, i.e. the "T" terminal

What there is a black wire there for beats me as the interior illumination operates off the shell of the instrument casing.

Unless you can find that this black is not earthed/grounded I advise missing it off and looking later to see if anything seems to need powering or grounding

AND NOW MY HEAD HURTS!

and I hope to have a quiet time relaxing...

good luck
Bill sdgpm

Thanks for the input. I did find B and T on the gauge (I need to get reading glasses, hate to admit it at 41 but I can't see anything close anymore).
Tried Green to B and Green/Black to T case is grounded (for the bulb) Gauge does not work, the needle flicks as I turn the ignition on but it stay on E. Oh well. I'll tackle that one down the road. I think you're right about the extra spade for the G, as a jumper to another device if needed, threw me off though. It makes sense other than it doesn't work anymore but we'll see, at least I'm convinced it's wired correctly.
J Van Dyke

Maybe the switch to negative earth is what the gauge doesn't like. I read it isn't supposed to matter but then I read others lost their fuel gauge after the conversion so, maybe that's the issue? Then I wonder if I can swap in a later model gauge without swapping out the sending unit?
J Van Dyke

Quick update. Green wire to B, and GB wire to T, "extra" black ground wire not used (in my case as ground is run from tach/speedo to fuel gauge mounting lug).
Don't know why pulling of the GB wire and putting it right back and it reads 1/2. Might be accurate, don't know what's in the tank anymore. Maybe a flaky ground somewhere yet. "seems" to be working.
J Van Dyke

It's possible that pulling the connection off and then refitting it cut through a film of copper corrosion along the tag and allowed a clean metal to metal contact thus letting the resistance measure as needed

I hope that works it for you

fingers (figuratively!!!) crossed

What's next?

:-)
Bill sdgpm

What's next? you ask?
Get the heater box back from the loser powder coating guy, who has had it for 2 months. Rig heater box valve cable. Button up the dash (for the last time for a while I hope). Install the XR700. Time ignition. Set valves. Tweak the Weber, install and play with the HS2s. Try out a Harley exhaust (Monza too loud for me). Install MKI trim (bonnet and side moldings). Redo rear speakers, play with some fronts. Put on fender mounted mirrors.....Drive the rubber off it.
Oh, I forgot, the ammeter freaked out, needle got stuck (physically I think on the edge of case, way way out on the + side, no idea why). I ordered up a cheap volt meter instead, so have to wire that in and break the things I fix in the process.
Oh, yeah only one headlight circuit works yet, for some reason, one of the relays is freaky or my wiring job stinks or something. Got to get passenger front parking light to go on again....They are brighter than before the relay though, and safer too I hope (providing the guy who did the wiring didn't do it stupidly).
Oh yeah, go after the oil leak on the spin on filter adapter.....it never ends does it?
J Van Dyke

not much then

:0

The voltmeter is dead easy to wire in...live power off the solenoid feed and earth(ground) the meter output wire, all it does is tell you the available voltage at the battery, and I would rather have that than an ammeter

(Opinions vary wildly about that though)

Nothing we won't be collectively able to help you with

J what does the J stand for? (and no gags about honour integrity and apple pie, perlease!)

We really do like to know this stuff

I'm not B I'm Bill

:-)
Bill sdgpm

J is for Jeff, or Geoff if I'm feeling British.
Yeah, the volt meter, found one on ebay, black face, white number, white needle, chrome ring right size, bought it. Dummy me it's at harbor freight up the street at 1/3 the price. Oh well.
I'll get it all sorted soon enough. Love to tinker so no frustration....yet.
J Van Dyke

This thread was discussed between 20/03/2009 and 24/03/2009

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