merchauser

not fully comprehending the volt gauge resistor: does the resistor effect both the gauge and the warning lamp, or only the lamp?

I would like to correct my dash gauge faulty reading and wonder in a new resistor could be the remedy? getting prepared to remove pod
and start my cleaning.

i have cleaned grounds, jump post, and 12+ at CE.

my multi meter readings at jump post, ABS, and top of CE read the same with car off 12.48, and with car running 13.71. not sure if it matters,
but at pin #1 (blue exciter wire) with car running i get a little more voltage: 13.88. next, I checked resistance from jump post to CE and got 0.1.

also to note, even though the dash gauge reading is inaccurate and lower, the gauge and the MM both show a .25 voltage difference between
a no load and load (AC, lights on, etc.) situation.

finally, is a resistor a binary pass or fail component, or is there grey area in between?



Gauge at idle is 12.25 which is approximately 1.5 volts lower

dr bob

Inspect/clean the ground point for the cluster at MPIV on the firewall. A weak connection will affect the voltmeter readings. Ground your DMM here for the voltage readings.


The low voltage reading at the cluster deserves a DMM reading at the CE panel 30 connection from the jump post to see how the voltage there compares with the cluster voltmeter reading. Clean those CE panel feeder connections. Always-on voltage to the cluster is via CE panel connection E11 and also connect to E12 (to pin 12 in the diagnostic connector only), fed by fuse 24 (always hot) from the CE panel 30 bus. Key-on voltage to the cluster is via CE panel connection B21 unfused, and at A25 via fuse 10. These are fed from the 15 bus (key in run or start position) from the ignition switch. Check voltage at all of those points, particularly the 15 circuit via B21 with engine running, to see how they match the voltmeter in the cluster.

IIRC there's a way to display system voltage on the digital display as part of a diagnostic sequence. I don't have the specifics of the diagnostic steps handy, unfortunately. They are in the WSM though, and I think in a supplemental tech pub.

merchauser

great info...thank you Dr. Bob! I will put the exciter lead in my rear view mirror.

using the MPIV ground for my mm, and on cold start, mm reads 13.75 at the CE, and dash gauge read 13.0 with no accessories on. however, within 5 minutes, the gauge goes down to 12.25. (this is the normal pattern, although most often, the dash reading drops to 12.25 by the time I leave my street) voltage at CE remained at 13.75.

at the points you suggested to check, most all read at 13.69 with very minor differences; gauge remained at 12.25, and when cooling fans came on, dropped to 12 or just a hair below.

there are times when for no significant reason, the dash gauge will float to 13, hold for 15 seconds, and then drop back to the 12 to 12.25 mark. there are also times when revving to 6k, the volt gauge will again rise to 13, and then settle back down...but not every time. i can sit at a light for 5 minutes, and upon take off, gauge may rise to 13, and then float down again....??? it appears i have a floater (lol) the gauge NEVER reads above 13 even though I always have 13.75 or so at CE, jump post, etc.

no matter, it seems I have a leak of voltage between .75, and 1.50 volts?

does any of what I describe have anything to do with the gauge resistor? any other areas to check? or perhaps I need to calibrate the gauge with my MM?

dr bob

Grab sheet 4 of the wiring diagrams and verify that the cluster-end connections have the same voltage as the CE connector ends. It's a Good Idea to clean the cluster connector with Deoxit too. There's nothing that's heat sensitive enough to offer the readings you share, so it's back to dirty connections.

The cooling fan feeders go through fuses 28 and 29 and right back out to the fan final-stages module at the front apron. Your gauge reading should not respond to fans running or not without seeing a change in the voltage at the points I listed; fan power is separate from the power for the CE panel unless there are wires crossed. Refresh my memory on whether you've been into the CE panel or the cluster for anything. If the wiring has been disturbed, it makes for more "fun" possibilities for the diagnosis effort.

merchauser

i was able to obtain better and more accurate readings at CE points you suggested. I took readings with key on, run, sequentially adding fan #4, AC, and high beams. not possible to post data chart properly, so i will consolidate my findings. With car running. B21, E11, E12, and top of CE all measure nearly similar at 13.6. A25 was reading 12.96, and within a few minutes, drifted down to 12.46. hmmmm. dash gauge would also drift down from initial 13 to 12.0. gauge seems to mirror A25 in drifting down, but to greater degree. A25 reading compared to dash gauge difference can range between .25 and .75. all the other points had a larger differential more often closer to 1.50.

additional testing reveals that A25 is consistently 1 full volt below all the other check points in both engine off and engine on modes.

dr bob

A25 is the voltage from the 15 bus through fuse 10. It's worthwhile testing voltage on fuse 10 with the fuse in place undisturbed, probing through the little test holes with a needle probe on your meter lead. OK to use a paper clip for this duty if you need to order a better probe and test leads kit for your meter. You are looking for both the voltage readings, and specifically for a difference between the two ends of the fuse that would point to a poor fuse connection in the panel.

The fuse sits electrically between B21 (straight 15 bus feed) and A25. Since you report that B21 does not drop and A25 does, the drop is in the fuse, the fuse holder, or the connecting wiring behind the CE panel. The 15 bus is a bridge behind the fuses, narrowing the possibility to the wire from bottom of fuse 10 and A25 --IF-- you don't see voltage difference across the installed fuse. Note that the actual current flow through fuse 10 and A25 is nominal, so any resistance at the fuse and fuseholder or at the connection at A25 will show up as a more significant voltage drop.

--OR--

Grab your DMM, Deoxit and fuse puller. Remove fuse 10 and carefully clean the fuse terminals and the fuse-holder terminals. Then lift connector A (after properly releasing the connector lock mechanism) and clean both the CE panel pins and the harness connector itself. Battery disconnected of course. These terminals are generally considered "self-wiping" so you get a little bit of cleaning through oxide layers when you merely remove and reinstall the fuse and connectors. A soft brass detailer's toothbrush is one of my favorite weapons for this doodie.


If the A connector and/or the fuse and fuseholder terminals look any less than clean and bright, consider cleaning ALL the fuses, holders and harness connections all at once. Do the grounds and feeders at the same time WYAIT. Most are amazed at all the little gremlins and symptoms that just go away with a good cleaning. It's certainly one of the more rewarding exercises. It's probably worth just lifting the CE panel to the bench for the fuse and socket work, unless you just really love working with your head in the footwell. You'll do a much better job with it sitting on the bench.

------

For those playing along at home, remember that the descriptions here are specific to the subject 1989 car. Other years may have similar terminals and connections, but there's no guarantee. Invest time studying the diagrams for your specific year, and make a similar diagnostic test plan based on your year if it doesn't happen to be a 1989 car you are diagnosing.

merchauser

DING DING DING....we have a winner...sort of......not sure what this means

When I pulled fuse 10, my flasher relay was rapidly clicking, along with my dash turn signal lamp; no exterior lamps were flashing. I pulled the flasher relay, and my reading at A25 is now matching the other check points at 13.6 AND my volt gauge is also reading correctly........what did i learn? not sure. is it simply a bad flasher relay? (A25 is also reading the same as other points with engine off and key on at about 12.5)

dr bob

Clean The MP-IV Ground Point.

merchauser

^^^^^I thoroughly cleaned MPIV yesterday.

Cleaned the flasher relay and receptacles with Deoxit, reinserted relay, and everything is great! DVM at A25 and dash gauge are matching each other at 13.6. I guess i should wait a few days to pop the cork, but after cleaning the flasher, the gauge is working properly. It also reads at 12v with key on, prior to start

I am still curious to know what exactly happened. removing fuse 10, disengaging that circuit, transfered power to the flasher relay? and enough power to trigger the dash turn signal lamp, but not the exterior lamps?

dr bob

The terminals for the fuse are "self-wiping". The terminals are beryllium copper, so they slowly build a layer of normally self-protecting oxide or salt that isn't a great conductor. The fuse has tinned blades so it also builds its own protective layer. When you remove and replace the fuse, sliding the fuse blade out and back into the beryllium copper, it scrubs off the 'protective' oxide layers if they aren't too thick and particularly aren't salty. So real bare metal on bare metal low-resistance junctions, and things suddenly pass current correctly again.

The hint on the ground point cleaning again considers that the flasher might be leaking some current internally, enough to show a drop across the fuse and fuse terminals. I've seen ground points that were supposedly "cleaned" where someone had just dragged a brush across the bolt and called it good. Meanwhile... the eye terminals are brass or maybe tin plated brass or copper, so they gather that same protective layer of corrosion, especially when you add moisture/humidity to the mix. The bolts are originally cadmium plated, designed to sacrifice the cad before the steel underneath start corroding. Three different metals in a sandwich, with moisture and electric currents passing through. What could possibly go wrong? Mr Galvanni, did you have a comment? Anyway, the ground points get disassembled, all the metal bits brightened with a soft metal brush, it all gets reassembled and snugged, with a smear of Vaseline over the top to buy a few more years of service before you get to do it all again.

Maybe the best lesson learned from this is how a very slight bit of oxidation, in what otherwise looks like a "clean" connection at the fuse, ends up being the cause of a funky dash reading and all this fun talking about it. A really great illustration about why we should be bolstering the value of Stan's DeOxit stock holdings, and cleaning the fuse and harness connector terminals in the CE panel. On some regular basis, before the more serious symptoms screw up our rides.


Have a safe holiday weekend!



dr bob

khalloudy

Sorry to sound a little uninformed what is the flasher relay and where is it exactly in the CE? My VM gauge always runs at 12V or below. When all is running it shows almost 10V while the reading in the engine and battery are about 12.9V on a hot day with AC and all lights and radio.

Speedtoys

Catching up...the pod contacts/plugs/etc have all been cleaned as well, and the gauge pins?

Rules of thumb...and all thumbs are different..but...remember that as you measure down the path the wire path stays long, and the wires themselves get thinner..it all starts adding up.Although resistance-free connections, wires and cables would be ideal, most of them will contain at least some voltage drop. If your manuals do not list voltage drop values, use the following as maximum limits:

• 0.00V across a connection
• 0.20V across a wire or cable
• 0.30V across a switch
• 0.10V at a ground
  
  
  I calibrate the resistor in the gauge with the gauge out, to a bench power supply. Then its 'accurate' to the health of the path current takes to it.
  
  As the alternator warms up right under the exhaust manifold the voltage regulator inside it is meant to lower output voltage with temp at the same time.
  

merchauser

the flasher relay referred to is the green relay that controls your turn signals and emergency flasher circuit.

strongly suggest you start at the beginning of this thread and carefully read dr bob's recommendations. sounds like you are experiencing a similar issue, but it could be for a completely different reason. it took me a while to go thru all the connectors/connections, but it was well worth it.

this has been a real thorn in my side for a long time and I am not sure I am acting like a child, or an old man: bottom line is that i am very happy camper. thank you dr bob (again)

Speedtoys

Yarp.

30-40yr old wires, dirt, corrosion....

Old car fun stuff.

khalloudy

Some days I feel like i should replace all the wiring on the car and start new I did put in a new CE panel a few years ago but the rest short of the injector harness is factory install on my 87 so it has a good 33 years on them. Never cleaned the GP or most contacts. Too little time unfortunately.