WallyP

Easy solution would be to just leave the standard bulb in the alternator warning light. There are an amazing number of connections in the circuit between the cluster and the alternator - a little resistance build-up in those connections can cause the alternator to be slow in coming on-line.

tmpusfugit

Going back many years in my electronics education this is how I recollect this works: The alternator is "excited" by current flow through the sensor wire and the light bulb/resistor. As Wally mentions there are several connections that can become more resistive via corrosion and lower the current flow to the alternator resulting in non-charging. In this case by replacing the bulb with an LED (LED will draw far less current than does an incandescent bulb) less current will flow which may also result in not charging. As designed after current flow occurs in the sensor the alternator then puts out 14 vdc +/- and current flow then ceases in the sensor circuit and the light goes out. The alternator is "self-exciting" after once energized. Using an LED leads to needing to change the value of the current resistor, as if I recall correctly the circuit needs to "draw" about 175-200 ma's to function correctly. It can certainly be made to work with LED's but I am not certain the results would be worth the effort.

One other thought comes to mind, the light bulb in the circuit varies in resistance with current flow, as does the brightness. This property does not exist in resistors nor in LED's. I am not certain if that behavior has anything to do with our circuit or not.....if it does we definitely need leave it alone...we used to call it the "rubber band effect" and used it in the design of early stepper motor control circuits, a couple of light years ago...

bronto

Yes. Possibly with different bulb/sockets for the back of the panel, but plugging directly into the factory harness at the side of the cluster.

My experience with these is minimal but it wasn't encouraging. I attempted to fix my speedometer, realized it wasn't simply a connection issue and put it all back together as carefully as I could. Yet the dash lights and high beam indicator no longer worked. When I took it to my wrench for another attempt at the speedo, he just rolled his eyes at the connection problems. When he put it back together the lights and high beams worked, but the alternator gauge is flaky. He's told me before that these things are really touchy back there. I seem to remember that the bulb sockets had to be tight for the connection to be made, but could easily be stripped if over tightened.

Seems to me this could be fixed. Bulb sockets with a more certain connection to ground for example, or a harness like you are doing with firm connections and real wire connectors. And the solder and circuits wouldn't crack on a printed circuit.

Needs to be plug & play though. If it isn't simpler and easier it isn't an improvement.

Opelotus

Agreed, the harness I made is not all that simple or easy to work with, although it is easier to diagnose because the wiring is all easily visible. I think the best method would be to make one harness for the gauges and another for the bulbs. Either way the plastic foil and stock connectors would need to be replaced.

Opelotus

Here's a question for all of you. 6 months ago when my alternator died, the charge lamp didn't light when the engine was running. Instead, ALL the warning lamps would flicker on and off once in awhile. I found out later that the reason all the lights came on was because the Central Informer computer takes a signal from the alternator to disable the bulb check. Alternator dies - no signal - CI does bulb check. When I pulled the alternator completely and ran the engine - all the warning lights stayed lit with engine running. So my question is what is the point of the charge lamp in this case?

I suppose it would still warn you if there is an overcharge situation, but as far as no/low charge, all the lights come on, and then the charge lamp has no significance because it doesn't "stand out" (for a lack of a better way to explain it).

jmartins

You inspired me... Mine is so bad, someone did some dirty job previously and US$ 300 plus international shipping and taxes (100% in my case) in a new one is too much. I'm pretty confident that I can do this job.

Opelotus

Go for it! It is a bit daunting at first, but once you study the wiring diagrams and become familiar with the circuits, the whole layout will make more sense.

jmartins

can someone help me on 1978 MT Euro Dash diagram ? I did some searching here, but only old posts with PM.

Thanks

jmartins

Do you have pics from the finished job ? Thanks !

Opelotus

Sorry for the late response, I missed the update to this thread. Here is a photo of the completed rewire. I have since added plastic connector covers to facilitate easier removal/reinstallation (see second photo). The cluster may look like spagetti, but the colored wires make power, ground, and signal identification alot easier. It's been about a year since the modification and everything still works perfectly!

z driver 88t

Wow! Definitely impressive. I had no idea the printed boards were NLA for 82-84. Thanks for this update - I missed this thread the first time through.

txhokie4life

I just picked up a 79 Instrument panel from a pick and pull.

It has a perfect mylar, but the connector tabs have been broken off.

I pulled it thinking that I would pay $100-150 for it ... $26.95 with a $2.50 core.
My poker face was severely stressed -- I paid as quickly as I could.
I think I did let out they probably wouldn't be seeing a core anytime soon.
Apparently they have fixed prices for all cars!

Still trying to determine the best way to fix the connector. (i've seen the posting here, just need to find a plastic donor pair).

My existing instrument cluster -- is a cluster F. The connector traces are pealing back
and some of the mylar is cracking causing delamination.

I have been able to get it to 100% work (at times) so I at least I know everything is working.

I haven't tested the pick and pull one yet.

Mike

Opelotus

IIRC it is possible to solder wires onto the tracings. Could be a quick fix if it works.

WallyP

Looking at the photos suggests that using good two-conductor speaker wire for the light hook-ups might make a neater installation.

Opelotus

I would agree with that. There are plenty of changes that could be made to this design, especially with the lighting portion. Furthermore, soldering onto the sides of the bulbs is a PITA to say the least.