15 replies to this topic

[Basseyy]

Hey all, first time posting here so go easy on me  . (Vehicle Make and year: Leyland Mini S 1978.)

 

I've spent the last few weekends creating a dash and attempting to install a SAAS Tachometer into my 1978 Leyland mini S with no luck, I'm hoping someone here has any clue or ideas that I might not have thought of going forward with what seems to be an oddly strange phenomenon.

Following the wiring instructions to a tee the RPM gauge will sit on the maximum (9000RPM) or flicker up and then down sporadically I have wired in a 10k OHM 1/2 Resistor in attempts to lower the "spike" but that also seemed to do nothing.

I've had the gauge work correctly only when using a separate battery (not the vehicles own power) using jumper leads connected directly to the Pos (+), and Neg (-) terminals of a spare motorcycle battery i had lying around with this setup the RPM gauge shows happily up on the tachometer using the -VE coil signal wire, however I cannot get it to operate using the vehicles own battery I'm honestly not sure how this is any different to the above how or why this would be the case. (I'm hoping someone smarter than me has dealt with or knows what the issue may potentially be)

 

I have the correct output from the negative side of the coil and the other connections are also correct as far as I am aware to add I am running a Lucas DLB101 coil with electronic ignition ( I believe it is a power spark system but am unsure as it was installed by the previous owner) any help on how to move forward what to test, change or check would be kindly appreciated.

 

[timmy850]

Where have you connected the tacho 12V power and ground on the mini?

[Basseyy]

I will attach some photos/schematics of the wiring for both setups with just the starting system only if that is of any help.

 

What has me stumped is I have tried jumper wires directly from the mini's own battery both  +VE and -VE were used to power the tachometer aswell as the black and white signal wire again now the tacometer just bounces around from 9000RPM up and down like crazy.

 

I also tried grounding the tacho to the mini's body earth point below the brake cylinder and using power from the solenoid hot side again the same situation a bouncing tacho that just max's out. 

 

I also tested the ground strap and points in the vehicle and the ground is around 0.07 on the lowest OHMs setting.

 

I did take some voltage (DC) readings on the signal wire coming from the -VE coil with the seperate external battery, I have 0.35v showing on my multimeter, whereas with the mini's own battery the voltage is higher jumping up and down from 2v - 10v range.

 

Being electronic ignition the Distributor black wire returns to the -ve side of the coil which is where im suspecting interference noise or something is happening but im not sure? 

[Basseyy]

Mind the rudimentary drawings hopefully they make sense.

Diagram one is the separate battery power and ground to the tacometer and seems to work.

Diagram 2 is the minis own power to a fuse box wired off the key and grounded to the body which doesn't seem to work

And the wiring diagram most relevant to what's in my mini currently

It has me stumped, unless it's electrical noise of some sort that needs to be filtered.

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[Lplus]

Not sure why you show body ground anywhere near the fusebox.  The "downstream" side of a fusebox is connected to items that need power, so any earthing effect is through the circuits of the items that need power, not direct to earth.

[Basseyy]

I get you, it's not the factory fuse box I'm simply just drawing how I've grounded it with jumpers in an attempt to understand why one circuit will work and the other does not?

[gazza82]

Most SAAS installation instructions say it only works with standard ignition systems but you said you did get it to work with the electronic ignition?

That would suggest a possible wiring issue on the car. Have you tried it with + & - jumpers direct from car battery rather than separate battery or fuse box?

[viz139]

You don't state which model of tacho your using but I had a quick look at a SAAS tacho wiring diagram and it showed  permanent  battery positive and an ignition positive. Your diagram only shows an ignition positive connected, you probably need both.

[timmy850]

I’ve got a SAAS volt gauge. The extra positive wire is so that the memory doesn’t forget which colour backlight you switched it to. There’s also the backlight which is supposed to have switched 12v

From memory I just crimped all 3 of these positive wires together, I disconnect my battery when I park it up so the memory function isn’t important and I don’t mind having the backlight on during the day

[Basseyy]

That is correct, for the sake of troubleshooting I have all 3 coloured wires connected to 12v the ground grounded and the black and white signal wire until the gauge signal wire being the black and white from the coils -ve.

I have heard back from the SAAS rep (Rob) who was super helpful and fired off a few things to test and try before giving him a ring back.

We have established that the signal wire is receiving interference in the circuit now it's just a matter of isolating where it's from and suppressing/filtering it out

The alternator has been isolated with no change, so that leaves the electronic ignition and coil, my assumption is the gauge is picking up the collapse from the coil where it can spike to +-400v I just need to find a way to suppress/filter it if anyone has any ideas I'm all ears

[Basseyy]

This is how the (DIS) is installed, I'm going to attempt to wire in a condenser in parallel with the -ve circuit and see if that makes any changes, aswell as try it on the signal wire also if need be it cant hurt.

This is the gauge being ran also to clear up any confusion:

https://www.shopsaas...-muscle-sg31632

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[Spider]

Can I suggest Testing the Tacho ?

If you have a 9 to 15 V AC Plugpack, or similar AC supply available, disconnect the Signal Wire from the Coil, and connect the AC Supply to Earth and the Signal Wire. Turn the key ON and the AC Power Supply, the Tacho should read bang on 3000 RPM.

If that's OK, then try another coil.

[Basseyy]

Tacho tested okay, might order a new coil and try that cant hurt to have a spare.

[viz139]

I find it strange that it worked at all from an independent battery as there was no return path for the signal current. I would have thought the two negatives would have to be joined on the two batteries used. To me it seems like there may be  a polarity or voltage problem and just to check that the car is indeed negative earth.  Next thing I would check is actual voltage at the gauge connections with everything connected first with the engine off and than with it running. connect the negative of the voltmeter directly to the car battery negative as a reference point and also measure the voltage at the gauge negative.

[Basseyy]

I'm just as confused as everyone else seems to be aha, I believe the coil -ve and (DIS) Ignition negative are connected and grounds through the engine to the body so I know the issue isn't the earth.

 

I can confirm it is negative earthed, I suppose I get to enjoy more time probing around i might have a play with a diode in the signal wires and maybe crack the oscilloscope out aswell.