Before I crawl under the dash

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str12-340

str12-340

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I am just getting my 70 Dart GT running. While it was apart I rebuilt the entire dash and gauges, assuming it's a lot easier to do out of the car, and because I had a bunch of non-stock wiring to accommodate and I wanted it to tuck up and be wired properly. I bought new temp and gas gauges from Hoffmans. There is a completely new wiring harness through out the car (M&H), and the sending units for gas and temp are new, as is a transistorized voltage limiter. Neither the gas or temp gauge move at all. What are the potential problems that I should be looking for when I crawl under the dash?
DSC01499.JPG


DSC01506.JPG
 
Check for a ground from cluster to car body. Alligator clips on a 18 gauge wire for testing is a friend.
 
How does the cluster and dash usually ground? There's new hardware for all the spots where the dash bolts on to the frame. The cluster screws to the dash through the plastic Bezel, is there a ground wire somewhere?

I've got my jumper wires ready!

Can I just clip to the studs at the back of the gauge, hook up another gauge and see if it works?
 
If you can pretest every single gauge prior to locking the dash back in place that is a win (Captain Obvious here) Plus you just can’t have to much light under there. Have your flashlights set up and tools within arms reach. Long needle nose pliers are also your friends! And plenty of zip ties to keep it routed how you want it. Does not hurt to have a helper handy. They can fetch whatever you forgot or need so you don’t have to unfold and climb back out! Good grounding is key key key. I typically sketch out a schematic prior to going under then take it with me, as I think I will remember this or that and invariably I forget. Good luck, working under dash is miserable unless you are a elf!
 
Unfortunately the dash is now in place (and the windshield installed). Fortunately there are no seats in it at this point so I can lie down all the way through. I'll second the lighting comment - there's a reason that I painted in inside of my black dash, gloss white...
 
str12-340 said:
How does the cluster and dash usually ground? There's new hardware for all the spots where the dash bolts on to the frame. The cluster screws to the dash through the plastic Bezel, is there a ground wire somewhere
Click to expand...
67 cluster is grounded by the screws that hold it to the metal dash. I believe later models (don't know when) changed that.

Technically you could just take a volt meter and clip to the 5-6 volt side a gauge post and look for a fluctuating voltage around 5-6 volts.


You can VERY temporarily like 1 to 2 seconds, ground the temp sender wire and look for guage movement.


In all reality if you rewired the car there are too many posible points of failure to count.

Basically you need to trace out the wires from end to end.



ALL THAT BEING SAID...


If both gauges fail it is either.

1. input voltage to the IVR
2. Output voltage from the IVR
3. Grounds
4. miswiring
5. 2 bad gauges (not likely)
6 2 bad senders (not likely)



Lastly.


If you have to crawl under the dash remove the front seat / seats 4 to 8 nuts and you will thank me!
 
I've been really happy with the M&H wiring in my other two Darts, so while it's possible, it isn't likely. A faulty IVR seems like a possibility. Is it OK to momentarily jump the IVR to see if the gauges jump? I assume I can ground the unit to the frame and if that works install a permanent ground wire. I'll try stuff tomorrow and let you know what happens. Thanks for your time and expertise.
 
I WOULD NOT jumper the IVR. NO!!! The gauges work (originally) off 5-6V "equivalent" AKA "pulsed" 12V at about 50% duty cycle.

Not trying to make fun but MAN I don't know why you would not have tested circuit by circuit as you wired them up

Something to tuck away............

When troubleshooting and there is the danger of either an unfused short (wiring smoke/ melt/ damage) or damage such as you are dealing with here (gauges) Wire an APPROPRIATE sized / wattage lamp in series with the battery ground.

The IVR by the way has a ground point (3 terminal) so screwing around bypassing it is a bit dangerous.

If you cannot get a gauge reading by grounding the sender terminal, then check if there is power (As Dana said) in and out of the IVR

Also I WOULD NOT use an OEM style (electro / mechanical) IVR. Buy one such as RTE. They used to be around 50 bucks, but may have gone up
 
Another issue(s) with all Mopar dash clusters "in general"

1...Grounding. As mentioned, the cluster is "accidently grounded" via the mounting screws. Attach a pigtail ground wire to a common point on the cluster (some of the PC board mounting screws are the ground trace) and ground that wire to the dash frame or better, the column mounting frame

2....IVR socket/ contacts. The IVR finger contacts can lose contact with the pc board traces. Solder jumpers across

3....Gauge terminals---these can corrode, and originally had those stupid "speed nuts." Apply "real" nuts and loosen/ tighten a few times to "scrub" the contact area and stud

4....Harness connector pins. These are rivet/ swedged to the board traces, and can come loose/ corrode. Clean and solder around them

When soldering older wiring/ terminals especially, use extra liquid flux. Be careful NOT to use anything for plumbing, which is acid core. Search "rosin flux" on ebay, there are folks selling small bottles. This is because Kester only has two options that I'm aware of---larger containers like gallons, or the "flux pens" which don't work too bad. But the pens have a felt tip like a marker and can become "frazzled" and contaminated with use on old wire/ terminals.

I like and still use older Kester "radio" designed solder "Kester 44"
 
67Dart273 said:
Another issue(s) with all Mopar dash clusters "in general"

1...Grounding. As mentioned, the cluster is "accidently grounded" via the mounting screws. Attach a pigtail ground wire to a common point on the cluster (some of the PC board mounting screws are the ground trace) and ground that wire to the dash frame or better, the column mounting frame

2....IVR socket/ contacts. The IVR finger contacts can lose contact with the pc board traces. Solder jumpers across

3....Gauge terminals---these can corrode, and originally had those stupid "speed nuts." Apply "real" nuts and loosen/ tighten a few times to "scrub" the contact area and stud

4....Harness connector pins. These are rivet/ swedged to the board traces, and can come loose/ corrode. Clean and solder around them

When soldering older wiring/ terminals especially, use extra liquid flux. Be careful NOT to use anything for plumbing, which is acid core. Search "rosin flux" on ebay, there are folks selling small bottles. This is because Kester only has two options that I'm aware of---larger containers like gallons, or the "flux pens" which don't work too bad. But the pens have a felt tip like a marker and can become "frazzled" and contaminated with use on old wire/ terminals.

I like and still use older Kester "radio" designed solder "Kester 44"
Click to expand...

Hey 67Dart273,

I'm pretty sure the dash is also grounded by a black wire in the harness that goes to the body on the passenger side foot well just behind the kick panel. At least that's where it is in my 68 Barracuda.
 
AAndrews said:
Hey 67Dart273,

I'm pretty sure the dash is also grounded by a black wire in the harness that goes to the body on the passenger side foot well just behind the kick panel. At least that's where it is in my 68 Barracuda.
Click to expand...
The ground wire you speak of grounds nothing but the heater core.
 
So here's the next installment. With the seat out, I crawled under the dash and with my faithful assistant (wife) watching the gauges, the engine up to temp, key in "run", while I wiggled and jiggled the dash unit plug, the IVR, played with the studs and nuts behind the gauges and neither needle even jiggled a bit. So here's my plan of action. Please yell if I'm doing something bad. I won't be able to get back to this for a week.

Here's the wiring diagram for that area:
70 Dart gauge wiring.jpeg

Question: Do these gauges operate by varying the ground at the sender? If I ground the gauge at the side of the gauge that goes to the sender, or at the wire connection at either sender should the gauge react? As long as this is on the voltage limited (5v) side of the equation, can I fry the gauges? I know how the fuel sender is grounded through the output tube and have installed a nice fat wire from it to the body, but how does the temp sender ground?

Check for 12v to the IVR

Check for 5v coming out of the IVR

Check for 5V at the feed side of the Fuel Gauge (at the post)

Check for 5V in and out of the multiwire plug behind the kick panel

Check for 5v at the plug that connects to the fuel sender

Then:
Check 5v to the feed side of the temp gauge

Check 5v at the plug on the sender

Check 5v at the input and output at the bulkhead connector


Remember all this stuff is new, so no corroded connectors. I assume if there is 12v into the IVR and nothing out, the IVR is bad. If something fails after that, either the new circuit board is toast, or a wire is broken. If there was a grounded wire that shouldn't be, I assume the gauge would be 'up' not 'down'? In the diagram the IVR has a ground but it must ground to the circuit board and I still don't understand how the circuit board grounds, or how the dash unit metal housing is grounded to the body.

Thanks for any further help that you can offer!
 
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