Sprint not starting

[John Larkin]

Further to my Sprint dying in traffic, I still have not been able to get it to start through the loom (but it does on jury-rigged wiring).

I removed the ignition switch yesterday. The wiring does not match the workshop manual (fewer wires, some different colours), although they look original. There was one broken brown wire connected to one of the ignition feed terminals with no insulating shroud on its spade connector, and I suspect it is not part of the original wiring.

There should have been two white wires instead of just one on these two ignition feed terminals --- one feeding one of the two fuses, and the other feeding the ignition coil via the tachometer. Instead the single white wire goes to a four-way bullet connector from which a feed goes to the tachometer and connects to one of three connectors on a recessed brown plastic thingy (voltage stabiliser??) at the rear of the tacho. Another white wire leaves that same brown plastic thing and goes to the coil, and it has seriously overheated --- it melted its insulating shroud. The melted plastic cemented the electrical connections together.

My wiring diagram shows four green wires connecting to the voltage stabiliser in the tachometer. I have found three wires --- two white and one green --- connected to the recessed brown plastic thing.

Is this the voltage stabiliser? Why does the feed to the ignition coil come from it? What happen when it fails? Any ideas why the output to the ignition coil should overheat?

I have cut two fingers on my left hand, and badly grazed my right wrist investigating this problem, and I'm feeling very sorry for myself.

Can some enlightened soul please help?

John Larkin

[types26/36]

a recessed brown plastic thingy (voltage stabiliser??) Is this the voltage stabiliser?John Larkin

John,
Search the recent threads as a pic of a v/stabilizer was posted recently, it is usually attached on the speedo holding bracket but I have seen them elsewhere. Lucas used a standard code for their wireing colours but a prevous owner could have changed things, the link below shows the code.
http://www.mgexperience.net/article/lucas-colours.html
Just to throw another factor in, Sprints have a factory fitted imobilizer switch in the glove box, I have heard of them giving problems with people disconnecting/by passing them although I have not had a problem.

Just found the pic.

[ppnelan]

John,

I think the 'recessed brown plastic thingy' is an insulating board that is part of the tachometer. The white wire from the ignition switch & bullet connector is the feed that passes through the tachometer. The other white wire that goes out to the coil is the 'other side' of this feed. It is the impulses from the coil in this loop that is sensed by the tachometer.

Not sure about the green wire - check the wiring diagrams, for earlier & later cars too if necessary.

The voltage stabiliser is a separate little unit that is (ususally) screwed to the back of the tachometer. See eBay item no. 130032682198 for a photo of something similar.

I would guess that the extra brown wire on the ignition switch is a live feed for a radio perhaps ?

If the coil wire has only overheated at the connector, it may just be that it was either broken here or it was not well attached to the connector. If the rest of the wire looks OK, I would cut it back by an inch or so (if you still have enough length to reach the coil!) and check if there are any signs of overheating there. If not, you can fit a new connector and try again. Otherwise there must be something else causing the overheating...

Good luck!
Matthew

[John Larkin]

Today at lunchtime I ran a temporary cable from the terminal on the tachometer to the coil, and I the car started and ran without a problem. The tachometer works just fine. So the culprit was the low tension "output" from the tacho --- the one with the melted insulating shroud. I'll have to trace the old cable and see what the problem was, as there must be an electrical discontinuity somewhere.

I'm still trying to reconcile the actual wiring with the diagram in the manual, although I suspect that this may prove to be a futile occupation. The Lotus wiring diagram seems to be more of a draft design intent instead of an as-installed drawing.

I appreciate very much the support and advice I have received on this forum.

Thanks again!

John Larkin

[ppnelan]

John,

I have found the Workshop Manual wiring diagrams to be quite accurate - it is usually home-made 'modifications' that cause confusion, especially if they have been done well and look like part of the original loom. I have also come across non-standard loom sections that look very professional but do not follow the Lotus wiring diagrams at all...

Good to hear you've solved it - finding out what's wrong is more than half the battle!

Best wishes,
Matthew

[Frank Howard]

John,

The white wire does not go directly from the tach to the coil. After it leaves the tach, it goes through the anti theft switch in the glove box, then it goes to the ballast resistor. A white/black wire jumps from the other side of the ballast resistor to the positive side of the coil. I'll bet your problem has something to do with that notoriously unreliable switch. Let us know.

Frank Howard
'71 S4 SE
Minnesota

[archigator]

Where does the white wire from the tach attach to the coil? Is this a white wire with a black tracer? (My '71 Sprint has no anti-theft switch; I think someone stole it... )

Gary
'71 Elan Sprint
Miami, FL

[Frank Howard]

Gary,

You are correct sir. After leaving the anti-theft switch, the white wire does not go to the coil. It goes to the ballast resistor. I have edited my previous post to incorporate your correction. Sorry for the confusion.

Frank Howard
'71 S4 SE
Minnesota