Rev-Counter/Ammeter Installation.

The Rovering Member

The Rovering Member

Well-Known Member
When I bought the Bruiser it had an after-market tachometer (& still does) as the guy I bought it from said that the original (S1) tacho had stopped working when they had installed electronic ignition. I've tried it too & it won't work. I have a spare but the wiring is different. The original has the white/black & white/yellow wires which plug in the back of the tacho & my spare has just the white/black wire which loops around the back of the unit. Can I just connect this in between the black & yellow wires & mores to the point can you use the S1 tachos with electronic ignition to start with?
Also, where would I take the wires from for an ammeter feed on a '69 S1?
 
The Series 1 tacho (with the loop behind) will work just fine with electronic ignition if it is for negative earth connection. At the moment i don't remember any wiring colours, but the idea is that the wire that leaves the dizzy to connect to the negative terminal on the coil, should go though that tacho loop first instead of going straight on. If you play a little with a multimeter and identify the wires it will be dead easy.

As for the ammeter it is a little tricky on a Series 1 car, because you actually have to run a rather heavy wire into the car to the ammeter. In series 2 cars this is avoided by using the famous "ammeter shunt" that actually senses the current and feeds the gauge you see.
Anyway, with the series 1 the idea is to connect the ammeter in line between the battery and pretty much all electrical consumption, bar the starter for obvious reasons! If i remember correctly the battery feeds the rest of the electrics through the starter solenoid. So it is a matter of connecting the ammeter between the starter solenoid and the feed to the rest of the wiring.
Also if you have a wiring diagram from a series 2 car handy you can chech how the ammeter shunt is wired and get an idea.

I hope that this helps...
 
Thanks Demitris. Of course I should also have mentioned that the car is now fitted with an alternator too. You are right that the main battery feed goes to the solenoid & I should also mention that an inertia starter is also fitted so AFAIK the old seperate solenoid is just acting as a junction now.
 
Sorry, I meant she's fitted with a pre-engaged starter motor, as you'd probably guessed. :oops:
Also, I can't see the tacho included in the workshop manual (1967) circuit diagrams though it is listed in the timed tasks. Is it possible my spare is a positive earth?
 
The rev counter has been introduced simultaneusly or after the change to negative earth, so if it's genuine it cannot be positive aerth. And in any case Smiths rev counters write on their face somewhere their polarity.
I found too also that for some strange reason rev counters are not mentioned in wiring diagrams for series 1 cars. However, they are connected as i told you, so you should have no problem with this.
My car is also converted to an alternator and pre-engaged starter (yes, i guessed you meant this :wink: ) and i have also retained the separate solenoid. However, this does not change the ammeter connection principles that i wrote above. In my case i connected the ammeter wires to the separate starter solenoid as i did not change anything to the wiring at the time that i converted to the pre engaged starter. I just pulled an extra wire from the separate solenoid to the solenoid on the starter.
 
No, they're not mentioned in the circuit diagrams at all are they? Strange. I got my spare tacho working though. It wouldn't when I connected it between the existing white/black & white/yellow wires but did when put just to the w/b one (the loop on the rear was the same wire) & another that I ran back from the -ve side of the coil (I tried the original one on this set-up too & it was still dead). It over-reads by about 1000rpm according to the other one which is still connected & I'm inclined to believe the aftermarket one as my P5B's rev-counter also ludicrously over-estimates the engine speed. I'm not too bothered, I just like it working & I'll keep the other one in there too as it's only a 2 inch one so will nestle in with the other gauges I plan to install.
I bought some 35amp wire today for the ammeter, is that a sufficient rating?
 
Glad that you had it working. You know with old cars you can never be sure when the previous owner made changes to the wiring. However, i am puzzled with the overreading issue. Mine seems to be fairly accurate. Do you think that it shows 1000 rpm more across the entire rev range? Then somebody could have messed with the needle. And you can rectify this. I do not remember offhand, but perhaps there is an adjustment srew or something at the back, have a look.

I am afraid that the 36A rated wire is not enough. Just think that this is the standard output of the standard 16 ACR alternator. If it has something newer it will be more. For a safery margin you should double that, avoiding also losses, because the wire will be rather long. Be careful on the routing of the wire, using rubber grommets and sleeves when necessary, because this is going to be permanently live and unfused (although you could include a 70A fuse in line). Also take care to solder properly all terminals and be sure that they fit tight.
You cannot be too careful with electricity.
 
Yes, I'll find out where the W/Y wire goes one day. It's roughly 1000rpm out but does fluctuate across the range so I don't think it's a straight indication problem. Apparently the P5B tacho's can be unreliable so I'm assuming the P6 ones being of the same period & manufacturer are the same. As for the ammeter the guy had some 60 amp wire but it looked too thick to me. Shows what I know. :)
 
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