Se5a Rolling rejuvenation project

If you have a long-term project and would like to share/document progress, this is for you.

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Re: Se5a Rolling rejuvenation project

Post by AnotherTim » Mon Jul 17, 2017 1:29 pm

Advice needed, welcomed....

A new development on my bouncing rev counter. Just went for a bit of a cobweb blaster and noticed something new about my bouncing rev counter. When I have either indicator on, it bounces more.

I know somebody recently referred to a part of the electrical system that is essential to the rev counter, but I've just been searching the forum and I can't find it. It seems pretty obvious to me now that the problem with my rev counter is not mechanical (I was assuming it was a worn cable end or a worn 'hole in the back of the clock'... now I am of a mind to think it could well be the electrical doo-dad that somebody mentioned on here in the last few weeks.

Would somebody mind reminding me what it is called, and if possible... whereabouts I will locate it on my car? (73 SE5a)

Much appreciated, ta very much etc etc.


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Re: Se5a Rolling rejuvenation project

Post by scimjim » Mon Jul 17, 2017 2:07 pm

Without going into the bowels of the monostable (because I don't know enough about it :-)) the tachometer senses the contact breaker opening and closing. There's a power supply from the ignition switch and an output to the coil (with the eureka wire to drop the voltage), then there's a power supply from the "ignition control" fuse which feeds lots of things like reverse lights, voltage stabiliser, rad fan, volts gauge, front wiper parking, overdrive, brake lights, indicators/hazards, HRW.


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Re: Se5a Rolling rejuvenation project

Post by rebel alliance » Mon Jul 17, 2017 2:15 pm

E mailed you tim



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Re: Se5a Rolling rejuvenation project

Post by philhoward » Mon Jul 17, 2017 2:19 pm

Check you've got an earth wire onto the tacho... can't remember if it's a ring terminal under one of the knurled nuts on the securing fingers (think so) or a separate spade terminal.


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Re: Se5a Rolling rejuvenation project

Post by scimjim » Mon Jul 17, 2017 2:21 pm

Separate spade to body - I think the ring terminal under the knurled nut is supposed to be the illumination earth but can't remember if the bulb holder is insulated against the tachometer body?


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Re: Se5a Rolling rejuvenation project

Post by AnotherTim » Mon Jul 17, 2017 4:00 pm

Thanks for these replies. I need to read them carefully as they currently leave me feeling a bit jibbery. In the interim I went and pressed home as many terminals and spade connectors as I could, and off on a tangent I found myself looking at my ancient fuse box again. I then had a look at the fuses in case I had a rattling connection. I discovered I had a few cracked fuses, and some at an ampage I don't have, so I went off to but a box of fuses from Clifford's. Unfortunately they don't have any 50amp fuses and apparently I need two. One was an odd one like a 50amp for the washer wiper (leading me to suspect I may have the wrong diagrammatic cap on my fuse box. So I have replaced one 50amp (the not-so-important one) with a 35 and have left the best 50amp in the (I think) ignition control.

But where this anecdote possibly overlaps is after replacing all the fuses (which were much looser between the terminals) I discovered my electric windows were dead, and nothing controlled by a dashboard switch worked anymore (lights, washers, wipers etc).

So all the fuses came back out, all the clips were sandpapered and squeezed together with my hammers, and then they all came back to life.

But now I've also discovered I have headlight problems, but that's a different story.

So it seems I'm going to have to tackle the spew of horror electrics under my dashboard, and try figure out what needs to be replaced to get my rev counter working, and maybe my speedo will come back to life too.

I might need to find somebody locally who's good with old car electrics. I really really don't have much of any chance of sorting this out.


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Re: Se5a Rolling rejuvenation project

Post by AnotherTim » Mon Jul 17, 2017 4:10 pm

My big problem with electrics is I can't be intuitive. I can look at a mechanical component and deduce some sense of function or purpose from the form. With electrics, its all wires that go into holes. Thousands of identical wires, hundreds of anonymous terminal or relay units. so when anyone says "You need to replace the bingbong bypass, its the red wire that goes into the flancase", I then have to look at all of the 1000 red wires and make a random guess about which one is the one going into the flancase. There is nothing to define them. You have to know before you start, where as with mechanical stuff you can venture in to it with the assurance that the components will tell you what they do and what condition they are in.

Electrics is all wires, and a hundred little plastic boxes that never say what they are.


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Re: Se5a Rolling rejuvenation project

Post by AnotherTim » Mon Jul 17, 2017 4:43 pm

Ehhhh, I just did a google search for a reliant scimitar monostable in the hope I might get to see what one looks like. All I got was Land rover washerwiper delay switches.

I don't suppose anyone happens to have a picture of a scimitar monostable kicking around that they could post?... I want to see what one looks like so I can look for it.


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Re: Se5a Rolling rejuvenation project

Post by philhoward » Mon Jul 17, 2017 4:51 pm

I thought is was a rough (it's 60's Automotive Electronics) integrator to be honest inside the tacho? The components inside though are from a bygone age - to the point you can't get modern equivalents (let alone originals) that behave exactly the same - or at least enough to work.

2 choices if you think the tacho is actually duff - a second hand replacement, or a Spiyda conversion board but that involves running a new sense wire from the coil -ve to the tacho (and joining the two existing wires together).


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Re: Se5a Rolling rejuvenation project

Post by scimjim » Mon Jul 17, 2017 5:43 pm

I thought 5a was RVC but is still an RVI?

Quick Google: RVI

Quite an informative page here


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Re: Se5a Rolling rejuvenation project

Post by AnotherTim » Mon Jul 17, 2017 5:51 pm

See, Idon't actually know if it's the tacho mechanism or the cable or an electrics fault. What I do know is...

1. Since a few months back the tacho bounces a lot at idle, but then seems to settle more at 3000-4000rpm. This to me suggested a weakening element where the cable and clock mate up. At lower revs the two mating parts, if worn, can slip and miss, making the clock bounce. At higher revs and therefore a greater rotational speed it gets some inertia so the bounce becomes less pronounced. Conclusion1: It's a clock or cable mechanical wear related problem.

except that

2. Today, by pure chance, I happened to notice that even at higher revs, if I indicate left or right, the needle bounces in a much more pronounced way, even at 3000-4000rpm. Switch the indicators on... off it goes. Switch them off... it settles again. So this reminded me of a chat I was either in, or that I read on here where the role ofthe electrical circuit was discussed in relation to the tacho... in that it then suggests it's an electrical signal fault. In that chat there was talk of some kind of control doo-dad somewhere that is responsible for a number of things including the ability of the rev counter to relay an accurate reading. Jim just referred to it as a monostable, but I have no idea what one looks like or where it is,and google is throwing up absolutely no links to follow, or images of one, to help me identify it.

Also, it's gone back to feeling a bit grotty and weak when I tried to start it when warm/hot again today. Not as bad as before, and it generally started first time but it took a bit longer to kick in to action and was certainly weaker at starting once warm. That leads me back to the mythical eureka bypass wire, which I tried to identify last time but was wrong... (or it was inconclusive as to whether the thing I showed on here was the eureka wire or something else).

That absolute lack of any ability on my part to discern between any given wire and any given electrical component really tells me I need to find a professional car electrician... otherwise I'm just going to be shooting in the dark and will spend weeks fiddling about and making lawdy-knows-what-else stop working in the meantime. I already seem to have lost my headlights with even a tentative fiddle today.

The problem with finding a 'general' car electrician...even one that claims to specialise in classic cars, is that I'll pay a small fortune and whilst s/he might be able to get my headlights working again, s/he'll probably have never heard of a eureka wire, and will just confidently tell me I don't need one then hand me a bill, leaving me back where I started, but possible with some headlights once more.

So I just need to spend a lot of time searching out a likely candidate local to me who I can give the car to and be confident they know what all this stuff is and does, and can say conclusively whether my tacho is electrics related, even whether my dead speedo is electrics related, and give it a really proper looking at to determine what, if anything is wrong, or what, if anything, is right.

I just really really REALLY really really hate electrics. I honestly can't even make any sense out of the advice offered so far. It's like handing me a bucket of wet spaghetti and telling me to rescue the spaghetti noodle called Steven without snapping it. All I see is a big bucket of spaghetti, wrapped around numerous meatballs, and my brain short circuits. :D


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Re: Se5a Rolling rejuvenation project

Post by scimjim » Mon Jul 17, 2017 6:37 pm

There is no cable to the tacho.


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Re: Se5a Rolling rejuvenation project

Post by AJL Electronics » Mon Jul 17, 2017 6:39 pm

scimjim wrote:There is no cable to the tacho.
Au contraire, there are many. ;-)


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Re: Se5a Rolling rejuvenation project

Post by scimjim » Mon Jul 17, 2017 6:40 pm

Start with earth points, remove, clean and refit (black wires bolted to metal parts of the chassis/car).

Then lift the fuse box to check the rear for signs of overheating (you've already cleaned the contacts and fuses).


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Current: SE5 (8Ball), TI SS1 (snotty), 1600 SS1 (G97), 1600 SS1 (C686CCR), 2.5TD SE5a (diesel 5a), 6 x random other SS1s.
Previous: SE5, 3 x SE5a, 2 x SE6a, 3 x SE6b, GTC, 2.9i GTC, 3 x 1600 SS1, 1300 SS1, Mk1 Ti Sabre, Mk1.5 CVH Sabre
Chief mechanic for: 1400 K series SS1 (Megan3), 1400 CVH EFi SS1 (Grawpy), Sabre/MX5 auto (The Flying Broomstick),
1300 SS1 (Number One) & Sarah's coupe.
CURE THE FAULT - NOT THE SYMPTOMS

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Re: Se5a Rolling rejuvenation project

Post by scimjim » Mon Jul 17, 2017 6:40 pm

AJL Electronics wrote:
scimjim wrote:There is no cable to the tacho.
Au contraire, there are many. ;-)
In the context of the preceding post :?


Jim King

Current: SE5 (8Ball), TI SS1 (snotty), 1600 SS1 (G97), 1600 SS1 (C686CCR), 2.5TD SE5a (diesel 5a), 6 x random other SS1s.
Previous: SE5, 3 x SE5a, 2 x SE6a, 3 x SE6b, GTC, 2.9i GTC, 3 x 1600 SS1, 1300 SS1, Mk1 Ti Sabre, Mk1.5 CVH Sabre
Chief mechanic for: 1400 K series SS1 (Megan3), 1400 CVH EFi SS1 (Grawpy), Sabre/MX5 auto (The Flying Broomstick),
1300 SS1 (Number One) & Sarah's coupe.
CURE THE FAULT - NOT THE SYMPTOMS

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