Electrical Gremlin?

-
belmateo

belmateo

Well-Known Member
Joined
Mar 29, 2008
Messages
2,343
Reaction score
413
Location
Belmont, California
I have a 68 Dart Convertible that has two concerns at the moment regarding electrical. First is the top switch....here is the scenario, the car is running fine and I jiggle the top switch because I notice the amp meter is not charging and the car suddenly dies with no power going to anything at all, not even the dome lights. After some time or if I disconnect the battery and reconnect it, everything works again. Second issue is the fuel gauge has been replaced with several good working gauges but still does not read correctly (always shows overfill) Can this be caused by the in tank sending unit?
I appreciate any help you can give!
Thanks
 
The loss of power sounds like a major connection.

1 What do you have for wiring diagrams / shop manual? If you don't have a genuine Chrysler shop manual (I don't mean Haynes, Chilton, etc) get one, either an original, reprint, or "on CD"

2 The closest diagram I found was 68 Barracuda for the 'vert. top. It shows the top control switch power comes off the ammeter, through a breaker on the vert switch

The loss of power is most likely either in the bulkhead connector, or the ammeter itself, IE connections, or the molded wire ends may be broken/ corroded internally

Please read this article which details the problems with Mopar bulkhead connectors and which also shows (down the page) a simplified diagram of how the main power comes in/ out the bulkhead

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

If you don't have a shop manual, (until you get one) you might be able to download some useful info here: Scroll down, some of the earlier posted links are broke, and have been reposted down the thread

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual%2C+download

Here's a 69 service manual from that page

[ame="http://www.abodyjoe.com/pictures/Misc.%20car%20info/69%20dodge%20service%20manual.pdf"]http://www.abodyjoe.com/pictures/Mis...e%20manual.pdf[/ame]

If you look at page 8-85, it shows a detail of the vert switch, but I don't think the switch itself is the trouble, most likely at the ammeter. The red from the switch/ breaker comes right off the ammeter.

Page 8-96 gives you the list for the complete wiring diagrams and the Dart instrument panel wiring is 8-102 and 103

Another problem with Mopar ammeters is not the actual stud connections but the ammeter ITSELF.

The ammeter is a simple device just a piece of brass for a shunt which generates a magnetic field. But this brass is NOT brazed or soldered to the studs, merely sort of "pressed", and it can work loose. In other words, the pressure of the nuts against the soft insulator of the PC board is supposed to hold it all together. If this mess gets loose, and then hot, which will make things MORE loose, you will have this sort of problem

A typical Mopar ammeter:

http://www.bradsnosparts.com/yahoo pics/120408 001b.jpg

Many of us have "thrown in the towel" done some form of ammeter bypass, and coverted to a voltmeter:

(This thread is long, but there's a LOT of good info in there of about 3 different styles of clusters)

http://www.forabodiesonly.com/mopar/showthread.php?t=119480&highlight=ammeter+conversion


3 The fuel gauge:

First thing to determine is "is it the gauge, wiring, the voltage limiter, or the sender?"

The voltage limiter gets power from the ignition switch, sends power to both fuel and temp gauges, and back through the sender wires to the senders (temp and fuel)

Probably the best way to check the gauge end of things is to buy some resistors at Radio shack. For example, you can buy 4 100 ohm, 1/2 watt resistors and put all 4 in parallel. Hook this from EITHER temp or fuel gauge sender wire to ground, and turn on the key. After about a minute, if everything is OK, you should get close to 1/2 scale, or mid scale, on the gauge.

The test resistances are:

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

Some info is a little different, but those are close enough.

It is a well known fact that typical modern "repop" fuel senders are horrendous for accuracy.
 
Everything going off is most likely the service disconnect ( male/female connector ) at the firewall.
The top switch wasn't so inadiquate when the car was new. Age , use, increased amp draw caused by a top frame that doesn't move as easy as it one did, all this takes its toll on the original electrical components.
If that wiggling the top switch makes a difference, that switch may be partialy closed and bleeding a small amount of current. Not enough to run the pump motor, just enough to keep it nice and warm. Warms the forementioned connector also.
To replace everything with new OEM components will likely work for a long time.
Adding realys, larger, wiring,etc.. to the top circuit might be a good plan but relays and everything else under the sun will fail eventually.
 
Thanks for the article about the bulkhead, I will check that first. I have used several different amp meters and even bypassed at one point so I will make the connection permanent and bypass the amp meter (already have a gauge for voltage). Can I use the standard fuseable link?
 
A fuel gauge that goes rapidly to the maximum position suggests the signal is shorted to ground somewhere. Short could be inside the sender. Disconnect the sender and turn the switch on. If the gauge moves at all the short is in the wiring. That signal wire is exposed in the trunk. I've seen them shorted to ground in there.
 
I don't think it's the wiring because it does not rise quickly, just slow and steady. How can I test the in tank sending unit?
 
belmateo said:
I don't think it's the wiring because it does not rise quickly, just slow and steady. How can I test the in tank sending unit?
Click to expand...

With an ohm meter. At full the sender should show 10 ohms resistance.
If you know there is a lot less than a full tank of fuel there higher ohms would be shown. 1/2 tank is 23 ohms. empty is 73 ohms. 80 ohms or more should equal no gauge responce.
 
RedFish said:
Everything going off is most likely the service disconnect ( male/female connector ) at the firewall.
.
Click to expand...

I agree and intended to emphasize that. This would be the one feeding in from the fuse link to the ammeter (red)
 
Several years ago I rewired the top motor circuits using relays. Keeping the original dash switch after internally cleaning and relubricating it with dielectric grease it is now the trigger for two relays, one up & one down. That old switch has to handle up to 30 amps when direct wired from factory and is rather hard to find an original replacement that is any good. By using relays to activate the top motor, a large electrical load is removed from the dash switch.

As for electrical power cutting out, the above folks have addressed that. My car had severe bulkhead connector problems causing similar electrical problems as yours requiring its replacement, and replacing the main power supply conductors (large red & black) from under hood to amp gage, and fuse block. I also have rewired the engine compartment, and some circuits under dash.

Once you repair or replace the wiring harness your car will become reliable once again. For now I would install a battery cutoff switch to use when car is parked, and hope the fire gods don’t visit your car before fixing its wiring.
 
Thanks for the help and advise FABO, will get on this early next week. I also forgot to mention no dash lights at night. Is that related?
 
I just looked under the hood and I can see copper on the fuseable link (copper is corroded) so I think it has been like that for some time. Anybody know what gauge link I need as I can't seem to find the factory one?
 
belmateo said:
Thanks for the help and advise FABO, will get on this early next week. I also forgot to mention no dash lights at night. Is that related?
Click to expand...

Here's how the dash lights work.

The headlight switch has TWO power sources. Headlight ONLY power comes from what is called the "in harness splice" which comes from the black wire on the ammeter

The tail/ park/ dash power comes to the switch from the tail fuse in the panel.

When the switch is in park or head, power is supplied to the dash light dimmer control (rheostat). This power is fed OUT of the dimmer on a tan wire to a separate fuse in the panel labeled "inst" The OUTput of this fuse, on several orange wires, feeds off to all dimmer controlled dash lamps

SO the first thing to do is turn the headlight switch to park or head, and make sure the park and tail lamps work.

Then twist the dimmer control to the left, which is maximum brightness

Next, put your meter/ test lamp on BOTH sides of the INST fuse in the panel (normally on one end of the panel) and this should now have power on both sides of the fuse.
 
belmateo said:
I just looked under the hood and I can see copper on the fuseable link (copper is corroded) so I think it has been like that for some time. Anybody know what gauge link I need as I can't seem to find the factory one?
Click to expand...

I think its 14 gauge. Check Year One if you want a replacement complete with the connector.
 
I had a few minutes late yesterday to look under the hood and tried to take the fusible link out for replacement. Problem is that I can't get it out of the connecter (multiple) that plugs into the bulkhead, also there is a heavy black wire that someone passed through the bulkhead but I didn't make note of what position it is. Any advise on how to remove the fusible link without destroying the connector? Can I get just a connector somewhere to replace this one?
 
Do you mean that you cannot get the plastic connector out of the mate in the firewall, or you can't get the individual terminal out of the connector?

It MIGHT have suffered enough heat damage that the connector is melted together.

The heavy black is most likely a repair from damage

Read this for ideas:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml
 
I can't get the terminal out of the connector. I looked at that link so that heavy black wire is probably from the Alternator. I used some needle nose pliers and pinched the end of the terminal to unlock it and was only able to move it about 1/8" then it stopped and there is heat damage on the backside of the that particular connection.
 
Dad replaced his fusible link in the bulkhead and I am pretty sure they squeeze together and it should pull out. Make sure you unplug the "block" of 8 connectors, it would probably make it easier to work on.
 
Thanks Steve,
I just finished reading the entire article about the weak wiring in these cars and will do what they suggest from the website:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

heading to the parts store now to get some fusible links and crimp and solder connectors. After I get this resolved I can move forward to see what is going on with the fuel gauge and dash lights.
Thanks to all!
 
Nah, I am not intimadated by it at all. But I have to admit it is getting harder to follow the wiring diagrams. Need stronger glasses I think!
 
belmateo said:
Nah, I am not intimadated by it at all. But I have to admit it is getting harder to follow the wiring diagrams. Need stronger glasses I think!
Click to expand...

What has helped me is my digital camera. My 67 manual is on CD, so it's not an issue, but for paper books, I simply get out the tripod and take a good clean shot of the page. Then I can blow it up on the computor, reprint larger, etc.

Here's an example. Now I admit to using a pretty good camera, but you don't NEED to use one that good. Any setup that will allow you to select the full resolution of the camera, and position it such that you can get the page to pretty much fill the frame will get you a great shot. Take care to get the page flat, use a small aperture for depth of field.

The original was taken with my Canon 7D, with a 17-55 2.8 lens, at f14.5. Depth of field is very short with closeups, and even a "wrinkle" on a page can defocus that part of the shot I also admit this is pretty his res. Even after initial crop, the shot was still over nearly 4600 X 4800 pixels or thereabouts

The first shot is a scaled down photo of the original crop, to show what the one photo looks like. The crop is a "full size" crop out of the original, to show how large it can be made.
 

Attachments

  • _MG_5852s.JPG
    117.9 KB · Views: 220
  • _MG_5852c.JPG
    83.3 KB · Views: 217
Pull the instrument cluster out and make sure that the wires are ok. I had a 69 valiant where the insulation somehow got melted off of the main wire from the battery feed of the alternator that feeds into the alt gage. The wire would then short out to the dash frame when going over bumps/ets. I was putting alternators and voltage regulators on it every six months until I found this and replaced the bad wires. Then never put another one on again after I got it fixed. It would not always short out, just here and there...
 
Okay, I have replaced the front harness and found that the previous owner bypassed the neutral safety switch ( what a moron). Anyway, got the fusible links installed and bypassed the amp gauge. Will work on the neutral switch next. I have checked the orange wire from the harness to the fuse box and it is good, will deal with dash lights once I get the battery connected. Put an ohm meter on the fuel sending unit and it read about 22 ohms. Is that correct for about a 3/4 full tank?
 
Wow RedFish, You are right. After I read your post, had to think back as to how much gas I put in. It ran out of gas and I put somewhere between 7-8 gallons in. So that would be correct? I also replaced all the gauges with new Equis that I took apart and expoxied to the original faces for a factory look. The hardest part was lining up the voltmeter to just show on the "C" side of the alt gauge at 13.8 volts. Equis has a fuel gauge made for Mopar so that was not an issue. The only requirement I had was 90 degree sweeps so they would match the dash in the Dart. Once I get the neutral switch wired I can check the dash lights.
 
You must log in or register to reply here.
-

Back
Top