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MG TD TF 1500 - OK, Who let the smoke out of the Lucas wiring?

So, was driving the TD today and saying to myself that it seemed to be running well. Got the leaky float valve sorted out and no more rough running.

"What's that smell?"

then

Crap! Smoke coming out from under the dash! Quick pull over, turn off the key and the engine doesn't stop. Quickly look under dash and start pulling melting wires apart and engine quits.

Was able to sort out the shorting wires and the MELTED choke cable and get home.

On the way home I noticed that the ammeter was acting like a tachometer. At idle it would read very low near zero and as the RPM went up so did the readings, peaking around +15-16 ish amps at around 45 MPH. It previously would flicker at idle and go to around +10 while driving

So, I have a bunch of wiring to repair but I also probably need to test the voltage regulator. It is a solid state unit my dad had installed by Wilton around Jan 2010. Should probably check the generator as well.

How do I go about checking this? I have a pretty good digital automotive multi-meter I just got. This one has the RPM and Dwell functions (the main reasons I got this one).

I'll have to figure a better way to corral the wiring. It had been zip tied to the frame in some places and zip tied to the starter and choke cables. It has always been a bit of a mess since, well, who knows?

As always, any help is greatly appreciated.

Stuart



S Grimm

Another Pic of the carnage.

S Grimm

First off you need to try to figure out if it was the wiring that shorted out or a device.

Those two wires besides the choke cable look suspect. Is it possible they rubbed on it and got exposed?

They look to be different gauges so if the short was somewhere else you would not think it would burn through in the same place but I am speculating.

And of course where they attach to would be the first devices to look over and isolate.

Did you find any other burnt areas?

And once you are sure you have fixed the offending part(s) if not the wiring, you need to make a hard decision if it's time to bite the bullet and replace the entire loom. But not until you are sure all the devices ar OK. You can even patch what you have and run it that way for awhile as a test case.
Christopher Couper

The shorting wires may have drained your battery and the generator and regulator were working overtime to recharge it thus the +15-16 amps showing. How long did it stay in this position? I check generators by disconnecting both leads running a jumper wire from the large terminal to the small terminal (the field terminal) and then a volt meter from the jumper wire to ground. Start engine at an idle and watch the voltage. It should rise slowly as you increase engine speed but not not exceed about 17 volts. If you get a rising voltage with engine speed your generator is likely OK and any charging issue is more likely with the regulator or the wiring.
John Quilter (TD8986)

OK

Got all of the wires repaired. Looks like the culprit was one of the windshield wiper wires that got exposed and grounded on the choke cable. My son was with me. I picked him up from school and he had his book bag on his lap. I think that's what pushed the exposed wire to ground.

Other wires near or on the cable got melted and shorted as well. The wires from the two little connectors on the dash for the trouble light were already long enough to connect but there was about a foot of extra wire connected with wire nuts that then went to their respective locations. Pulled out all the extra melted wire and cleaned it up a bit as well.

Started up the car and initially the ammeter showed about 15 amps at 2500 RPM. After a few minutes it dropped to around 10 and hung out there even running the RPM to 3000. John, I think you are right about the battery being drained. That choke cable was so hot it melted and separated. Probably full amps from the battery acting like a welder. I think I lucked out.

Well, gotta go order a new choke cable and cable stop (the one on the car is wearing through where it passes through the jet lever).

Stuart
S Grimm

Replaced my single wire choke cable a year or so ago with the stranded type which is much more flexible and works much more smoothly.

Once heard of someone (not me) whose engine ground cable went open circuit and the full amperage of the starter motor went through the choke cable and melted it. A new phenomena, letting the smoke out of the choke cable.
John Quilter (TD8986)

I'd check your ground connections. It looks to me like the choke cable was acting as the ground source and when they do they get glowing red hot. I think that was the source of the melting wires.
L E D LaVerne

I second LaVerne. Not sure the tiny wiper wire could alone flow enough current to melt the cable. The ground strap from the chassis to the engine is on the left side at the base of the frame to bulkhead bracket, and to a tranny bellhousing bolt. I have removed them using an engine hoist... so some are missing! George
George Butz III

A short search has turned up no sign of the ground strap. I looked on the right and left side of the engine where the transmission connects. Is it hidden out of view? Someplace obvious?

Can someone post a picture of where this thing is and also give some recommendations for an alternate location of the strap. I'd rather not spend a month taking the car apart just to put a new grounding strap in.

Thanks

S Grimm

I went ahead an ordered a new grounding strap. If there is one somewhere else, it won't hurt to have a second one.

My plan is to attach it to the bolt just to the right of the plastic wire cover (bolt is vertical) at the black of the block. I think I can get at it from underneath the car without any problems. The other end will go on the bolt just right of the yellow butt connector diagonally up a bit.

Good thing I'm going to work for a week. All the parts should be here before I get home.

Stuart


S Grimm

Here's a pic of the ground strap attached to the bellhousing not yet attached to the bulk head bracket also not installed.

The strap was usually installed on the bolt tucked under the toe board.

two pics

Frank

TF1414

Frank Cronin

pic 2

The ground strap in this pic is "in your face" but you can see somewhat where it is attached .

Frank Cronin

View of original ground strap shooting straight down with body off of the car. Bellhousing bolt at the top, rear "tower" mount bolt edge at bottom of strap. Not exactly easy to get to with the car assembled.

George Butz III

Good call on the missing ground strap.
Christopher Couper

All fixed. Got the new choke cable fitted. Works way better than the old one. The choke return springs actually work now ;). Also installed the new ground strap. Still not sure if there is one already, couldn't find it, but a second won't hurt anything. The ammeter also reads about 6-8 amps regardless of RPM once everything settles down after start.

Now on to the next issue. See the new thread.

Thanks

Stuart
S Grimm

Photo of my ground earth strap from bell housing to tower mount. Cheers John

J.K. Chester-Freeman

install a battery cut off switch !!! Mine is attached to the hoop under the dash,, easy to reach as soon as you think there is trouble,, The battery is cut off before the car even stops!
Steve
SPW Wincze

Steve, you extended the cables into the car?

I am thinking of doing that with the ground cable.

Peter
P G Gilvarry

This thread was discussed between 05/09/2019 and 28/09/2019

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