[DINGBAT]

Hello again Gentlemen,
This might be one for the electric boffin,s
The 72 Rallye has an aftermarket Tacho with shift light etc installed.
Recently it has started to bounce around the dial with a mind of its own with no compatability to the engine revolutions.
I assumed the unit was faulty so disconnected it & connected the in dash one back. This is doing the same thing so the fault appears to lie elsewhere.
I changed the coil this made no difference so I refit the origional. I checked the grounding of the voltage regulator this was ok but still no joy.
The voltage to the battery when started cold this morning was 15.5 this went to 14.7 when the car was ran & warmed up so I would think all is well in that department.
Any ideas would be appreciated.
Best Regards
Pat.
Incidently if Dave sees this post I was at the Nats last year with the AMCI lads. I rambled around a lot in the company of Wayne AKA RedRaven.
I seen your car up close on a couple of occasions & must compliment you on same. Its really is a work of art & engineering.

[dave-r]

Hello!

First question is what kind of ignition system have you got?

The coil fires the spark plugs every time the negative side of the coil looses its connection to ground by the points (or transistor if electronic ignition) opening.

The tach is connected to the same side of the coil and so gets its signal in the same way i.e. it is counting how many times the circuit to ground is broken.

Now that is how it should work but you would get this same thing even if the positive side was going off and on as well.

So if you are getting an erratic signal the coil circuit must be erratic at some point. i.e. the negative or positive side has a bad connection.

If you are using a multiple spark type electronic ignition you will have the same problem if the tach is not designed to be used with such a system.

[DINGBAT]

Thank,s for the reply Dave.
I am near certain the ignition system is the standard electronic type as origional.
There are no red MSD type modules mounted anywhere in the car.
There is one ballast resister mounted onto the coil retaining bracket and connected into the coil circuitry.
However there is another ballast resister mounted onto the bukhead with some connected wires running into the system and a couple of wires blanked of.
Not sure if these would help cause the problem.
The system did work fine untill recently so I would assume the ign type and tacho were compatable.
I will take a couple of photos tomorrow of the bits & bobs and post them it may help.
I know that to diagnose & pinpoint the cause of the problem over the net may be nigh on impossible as in reality with your experience if the car was beside you the fault would be found and remedied post haste.
Thank,s again for your help.

[dave-r]

I am near certain the ignition system is the standard electronic type as origional.

Electronic ignition was not standard until the 1973 model year.

There is one ballast resister mounted onto the coil retaining bracket and connected into the coil circuitry.

Not the standard location for a resistor.

However there is another ballast resister mounted onto the bukhead with some connected wires running into the system and a couple of wires blanked of.

That is the standard location.

Not sure if these would help cause the problem.

Well probably yes. The wiring has been chopped about and now you have a bad connection somewhere. It sounds to me that you need to pull off all those wires and resistors and start again from scratch. I bet there are lots of crimped or twisted connections and bits of odd wire added in. You just need to start from basics and put it right.

A lot of these cars are like this. The wiring can be terrible after years and years of have-a-go cowboys "fixing" and modifying the original wiring. Plus the original wires themselves will be old and corroded.

If the car is a "keeper" it is probably worth getting a new engine wiring harness for it.

[DINGBAT]

I will strip back some of the wiring covering and trace the ballast wires during the week.
I believe the elec ign is a Mopar aftermarket jobby.
Silver unit on bulkhead to the right of voltage reg ?
Cheers
Pat

[dave-r]

Where is the coil? I thought you said there was a resistor on the coil?

I can see the bulkhead in your photo. On there from left to right you have;
An extra ballast resistor for some reason, the Electronic Ignition unit, the voltage regulator (polished) and a stock ballast resistor in the correct position.

[DINGBAT]

The coil is behind the ballast resister on the L/H side.
It is black in colour so hard to make out but you can see the h/t lead exiting from the R/H side.

[Jon]

Nice looking engine bay. For what it's worth my FBO ignition caused a double fire at idle problem. The tach reads twice the engine speed at idle then fine anywhere after 2000 RPMs.

[dave-r]

Nice looking engine bay. For what it's worth my FBO ignition caused a double fire at idle problem. The tach reads twice the engine speed at idle then fine anywhere after 2000 RPMs.

My FBO system is fine at idle. But the first ECU failed and I had to get a replacement.

[dave-r]

The coil is behind the ballast resister on the L/H side.
It is black in colour so hard to make out but you can see the h/t lead exiting from the R/H side.

Well it looks like that is the correct resistor for that coil. But why the nugget that fitted it did not just replace the original resistor with that one I cannot imagine.

Make sure there is nothing going through the original resistor because you do not want the current going through both. You may not have enough voltage at the coil.

However this is not your problem. If you cannot find a bad electrical connection I would be at a loss to explain what is causing the fault.

[DINGBAT]

Greeting,s.
I striped back the covering on all the engine bay ignition wiring earlier and can only assume it was wired ad hoc.
It appears to have been using 2 no ballast resistors in series with botchy wiring.

One ballast resistor is a dual pole the other an origional 4 pole.
The ECU has 4 wire running out with the 5th having been cut tight which I understand may be the norm.

The alternator / VR has 1 wire running out to the immediate area.

From the bulkhead there are two wires to the immediate area.
1 Brown/Blue which stays dead with the ignition on.
1 Orange which goes live with the ignition on.

I have checked 2 drawings in relation to wiring either of the resistors and both of them conflict.

I would prefer to utilise the origional 4 pole unit but the Dodge Service manual shows the need for 5 wires coming from the ECU.

The drawing for the dual pole resistor does not show the V/R wiring, and shows 2 wires from the bulkhead going live with the ign on.

Stumpted.

[dave-r]

Start from scratch.

Use the two pole ballast resister that most likely came with the coil.

Find out which wire is from IGN 1 and which from IGN2. The former (IGN1) is on when the car is running normally and is usually blue in colour. The latter (IGN2) is live when you crank the engine and is usually brown.

Connect the coil +ve to one side of the resistor. Also connect IGN2 to that same side.

Connect IGN1 to the other end of the resistor along with the blue wire from your ECU and the blue wire from your voltage regulator.

The black wire from the ECU you connect to the coil -ve along with the wire for the tach if you have one. the two other wires on the ECu are for the dizzy sensor. the 5th wire you do not need. just make sure the ECU body has a good ground to the sheet metal.

The green wire on the voltage regulator needs to go to one of the field connections on your alternator. The other field on the alternator can just go to ground.

This diagram should help.

[dave-r]

Hope I got that right because i get confused easily these days. I used to know this stuff off by heart.

[ianandjess]

thats a good diagram dave thanks for posting it im sure it will help simplify things for us
cheers ian

[DINGBAT]

Cheer,s Thank you.

[dave-r]

The black wire from the ECU you connect to the coil -ve along with the wire for the tach if you have one.

That was a stupid thing to say in a thread about the tach not working.

Told you I was a bit slow these days.

[DINGBAT]

Dave,
Apologies for the extended thread in relation to a problem many would find a simple fix.
I started fom scratch and scrapped the 4 pole resistor.
The 2 wires from the firewall
The blue with browntracer turns live on cranking
The Orange (Brown?) is live with the ign on.
Connected all as drawing & info and all seems well i.e no bouncing tacho.
The eng was only idling for approx 3 minutes and the ballast resistor got fairly hot.
If this is the norm then all is well.
Regards
Pat.

[dave-r]

Yes the resistor gets hot which is why it is in a ceramic case. As it heats its resistance goes up and so limits the current to the coil as coils are not usually designed to run on 12-14 volts. You only want the full voltage to the coil when cranking as cranking the starter puts a high load on the battery and pulls the voltage down anyway.

[DINGBAT]

Jeez these Mop,s are more fun than a barrell full of drunk monkeys.
After sorting out the ballast & tacho problem I took the car for a run yesterday only for it to cut out miles from nowhere.
No power at ignition switch, no cranking, zippo.
After checking all the usual suspects I found a wee brass element on the drivers floor, 1/4 spade one end & 1/2 moon loop the other end.
On checking some other posts in the electrical end of the forum I see 2 of these boyo,s in the photo shown, as part of the switch set up.
Would any member know.
What is their function
Can they be refit without stripping out the column similar to the changing the ign barrell thread.
To get home I ran a wire from the + coil to the + battery and cranked via the fender solonoid connections.
Not sure if this is method is recommended but it done the trick.

[dave-r]

If you are refering to the two spare wires in that photo I think they are for the optional "key in" buzzer. So nothing to do with your problem.

You need to find where you have lost the battery feed to the ignition switch. That is one of the thick wires on that connector. I can't remember the colour offhand. See if you have volts on the feed side of that connector. If not you need to look at the wiring diagram to see where it is fed from.

[dave-r]

One very weak spot is the feed from the starter relay (via fusable link) to the bulkhead connector and then to the ammeter in the dash. I think everything electrical in the car runs from that feed. So a bad connection at the bulkhead connector (which is very common) or a faulty ammeter can cause you big problems. It is the only bad thing about Mopar electrics.

The common cure is to wire around the connector. I also run a fused wire direct from the output on the alternator to the starter relay.

http://www.madelectrical.com/electrical ... uges.shtml

[DINGBAT]

I also run a fused wire direct from the output on the alternator to the starter relay.

Dave, Would this relief bypass be fused in relation to the output of the alternator.?
Cheers.

[dave-r]

Can you re-phrase? I don't get your meaning.

[DINGBAT]

Can you re-phrase? I don't get your meaning.

The additional wire ran from the alt batt terminal to the starter relay to help divert the full current from running directly through the bulkhead / alt guage etc. What rated fuse would be used on this.

[dave-r]

Gotcha. 30 amp will probably do it but higher would probably be better. It depends on what your normal load is.

I would modify the original wire (which has a fused link) to run through the bulkhead and by-pass the ammeter too. Then also run the other wire direct from the Alt to the starter realay with a 30 amp fuse. That way you are using two wires and each wire only carries half the load. So no worries about overloading one.

[DINGBAT]

I had a chance to check the ignition main Red wire feed today.
Okay from the battery via fuse link to bulkhead.
Okay running from bulkhead up to the underside of the dash.
Coming out into the 8 pin ignition plug was ok, but exiting the other side was dead with visible heat damage on the plastic connector.
Giving the connector a good wriggle restored the power Eureka.
The plastic plug appears to be fused together from the heat over a period of years, so the only way to sort the problem was to cut the mains on both sides of the connector and insert & splice a section of wire of similar dimension between the 2.
To bypass the Alt guage looks like a dash pull which I am not to confident about tackling. Murphy,s law I,ll fix one thing and break something else.
So I pulled all the bulkhead connectors & checked & cleaned same.
In appearance they looked clean and solid.
I ran a piece of 30amp fused wire from the Alt Bat terminal to the starter relay to help with the dispersal of the current per another thread.
I also replaced the Ballast resistor with a new one.
With the car well warmed and running at 1500rpm the following showed on the test meter.
Battery showed 14.7 volts
Alt output 14.7 volts
+ on coil 10.6 volts.
I hope these are within the safe operating range.
Incidentley the tacho stayed perfect with this alt to battery addition when taken out the bugger started bouncing again. So in it stays.

Cheers

[dave-r]

Sounds like you have got it well sussed out now.

I have been having problems with my ignition system recently. It decided to just stop working one night. However it has been working fine since. If it plays up again anytime I am going to fit a Chevy HEI module instead. They work better anyway.