Factory gauges bouncing

[JHyneman]

I have a 1984 crewcab with a 1993 wiring harness in the truck and drivetrain. Driving down the road the water temp gauge starts bouncing, the volt meter bounces and the radio light flickers, if the radio is on it gets really bad static when this happens. At night the headlights will also surge. At idle every thing acts normal. Now before you all start telling me to check my grounds in the engine bay, I have replaced all my grounds and even tried an external voltage regulator. The problem has to exist under the dash because I even tried a spare engine, engine bay harness and a different computer and I also replaced the cps. Now under the dash I checked the grounds athe emergency brake, headlights, and the ground on the dash frame on the right side if the column. All those grounds check good after cleaning them and ohming them out. HELP

 

[JLEONARD]

Check your grounds. Only kidding.
I had an old Chevy truck that used to do that. It had an old adjustable mechanical style voltage regulator with a weak spring and the contacts would open/close at certain rpm. Since you change
d voltage regulators I would suggest testing the alternator.

 

[DVolk]

Were the connections all clean ? i use Electric terminal cleaner all the time . Are you shure you dont have a water leak getting wires wet and causeing a short also that there is no corosion in the firewall block , i had a gas rig that had one bad spade one that i had to bi pass once

 

[JHyneman]

Check your grounds. Only kidding.
I had an old Chevy truck that used to do that. It had an old adjustable mechanical style voltage regulator with a weak spring and the contacts would open/close at certain rpm. Since you change
d voltage regulators I would suggest testing the alternator.

I could see a diode in the alternator going bad giving a bouncing voltage all the time but why would it only be bouncing when accelerating under engine load, and would it affect the water temp and radio and lights? I will have it checked but I am just confused.
When the drivetrain was in the 93 I didn't have this problem. Since the swap 4 months ago is has been garaged so water would not have gotten in the wires. When I swapped the engine harness yesterday to check it out I cleaned all connectors on computer and bulkhead connector then applied a thin coat of dielectric grease.

 

[JHyneman]

Ok so I had a chance to check the diodes in the alternator and they both check good. Autozone testers said my regulator was bad. I don't think so. Put 2 different external regulators in and tested the factory regulator and all charge at the same voltage. Even had the battery checked too.

 

[JHyneman]

I had to use the truck for a tow last friday and the problem appears to be getting worse. I have noticed that the problem gets worse as the truck warms up. Bouncy roads cause the gauges to bounce worse. The radio time and memory reset several times over the 3 hour trip and the oil pressure gauge would peg out, when all the the gauges and radio lost power the speedo would slow down. My gps said I was doing 65 but the speedo was saying 45, but when the gauges smoothed out the speedo was dead on. It appears to be a loss of voltage instead of a surge of voltage. I pulled the fuse panel and found that the fuse in my a/c slot was melted but now blown. I don't know if this has anything to do with this issue. HELP PLEASE

 

[DVolk]

If fuses are getting melted you have a serious issue , some place either a bad harness or something .
Do you have the cab grounded to the engine or frame or both . , you might think about going to aftermarket guages or back to the 84 wiring harness as the engine dont need the 93 one to run

 

[JHyneman]

If fuses are getting melted you have a serious issue , some place either a bad harness or something .
Do you have the cab grounded to the engine or frame or both . , you might think about going to aftermarket guages or back to the 84 wiring harness as the engine dont need the 93 one to run

I think the fuses melting is due to the incorrect fuse being installed.
The dash, cab, frame,fenders, and engine are all grounded together and then to the engine.
The 84 wiring harness was tossed. It had over 2 dosen wire nuts holding it together.

Could the ignition switch be out of alignment causing a intermittent power failure in the run position?

 

[DVolk]

Its possible one test for that or rather two i know of on the colom take off the switch its self , get a nail or small screw driver
and insert it in the hole and start and run the truck and if you like drive it if its a alinemet problem it should act if all is normal
How ever if t acts up then id try this one take a jumper wire and go from the positive of the batt to the fuel shut off , it wont shut off until you pull the jumper off unless you have some huge electrile issue or you have a bad fuel shut off sylinoid .

 

[JHyneman]

Ok so I have finally fixed my problem and tested my fix. Put on 80 miles trouble free. My gauge cluster was the culprit. My cluster came out of a 91.5 automatic. The speedometer is different than the 93. My 93 speedo has more circuit board than the 91.5 which appears to be more mechanical. However they work swapping the speedometer did the trick and fixed my problems.

 

[RSchwarzli]

So the non IC clusters are different. Interesting. Nice find. That would have taken me a while! Lol

 

[JHyneman]

Yes they are different but even with the inter cooled clusters between 91.5 and 92 are different than 93. I found it by looking at things that I replaced in the '93. That was the gauge cluster, I replaces it because the cas was all cracked.

 

[RSchwarzli]

Oh good lord. That is not very Dodge like to make that many changes! lol