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This beast is giving me a headache. I have power from the instrument fuse to the connector in the back of the instrument panel-DVOM shows 8.60 volts, with the engine off, on the instrument connector on the chassis side. (All contacts are clean and zero corrosion) The wire is light blue with a red tracer. Oddly enough the turn indicator lights work as does the seat belt warning light. I cannot find any burned out tracks in the printed circuit or burns of any sort. All bulbs are good. Truck sat for 6 years and now this. Dash ground is clean and tight. Is there some way to test the printed circuit for continuity?
If not, maybe the rheostat on the headlight switch isn't passing enough current to light the lamps but is passing just enough to get a voltage reading with a high input impedance DVM
No Michael they do not illuminate.However the lamp for the headlight switch and wiper motor does as it is not connected to the printed circuit. It also turns up and down with the rheostat, however it is not real bright. I haven't checked it with the meter however but can in the AM. It would seem to me the dash lights would get full voltage not what I measured at the connector at the back of the cluster of 8.6 volts. Was using a Fluke 88 if it matters. I still cannot understand why the seat belt light works as do the turn indicator lights which all work off the printed circuit. One other light I need to test is the high beam indicator. Anyway full day and need rest. Thank you for the quick response.
I think I have a clue, maybe. The headlight and wiper switches get power directly from the dash light fuse. All other lights go through a plug or 2. But what confuses me is that you are getting some voltage at the printed circuit plug. The diagram doesn't show it clearly but the lights that do work may have a different ground from the dash lights.
You won't get full battery voltage unless the rheostat is cranked fully clockwise, just before the dome lamp comes on, and then only if the wiper and contact are really clean.
Here is a snip of the diagram. I don't know if the point where wire 19 splits up to the dash lights, PRNDL and heater is really a 3 pin socket or not.
Thanks again Michael for the assist. The wipers do not work either. Nor does the heater blower unless I manually press the contacts in the relay together then the blower works in all speed ranges fine. ( I took the cover off the relay itself). What is odd is the relay is powered with the key off or on. Been pulling my hair out on that problem as well with the onset of Winter coming on.
With respect to the dash light problem I am going to clean all contacts with alcohol and see if that stirs up anything.
There are only two bulbs to illuminate the gauges, so maybe they burned out. Also check your cluster back for cracking and disintegration, which could cause contacts to no longer be in contact.
Thanks meangreen. I replaced all the bulbs then cleaned all the contacts and I got one of the two actual gauge lights working but soon as I wiggled the bulb connector it went off. So cleaned the copper contacts on the printed circuit and have never been able to get it lit again. Seems as though there is a crack affecting the two dash lights in the printed circuit. I even lightly cleaned the copper with 500 grit wet/dry sandpaper. Simply no power coming through when I checked with the DVOM at both gauge lights on the printed copper circuit. That film is my main suspect.
I just fought this problem on my 1974 f350 SCS. IT too had sat for a long time in damp weather. My fan issue turned out to be the fuse itself had an intermittent failure. Replace and cleaned the contacts and got fan/defrost etc. fought the lights. Had dim heat panel PRNDL and Light/wiper but no dash. Chased to headlight switch. Replaced switch and got right half of gauges to light up and got more brightness from other bulbs. Still hasn't figures why only left half of dash is not lit but everything else is. It can be very frustrating but corrosion on the fuse block and corrosion in the switches can do funny things. Good Luck!!!
garry
You can bend the little copper contacts on the bulb holders so that they make a more positive (read heavy) contact with the IP PCB. I had to do this to a few on my truck.
Also make sure that the blue/red gauge light circuit wire's terminal is making good contact where the harness connector plugs into the cluster back/IC PCB.
Rich, do you have a diagram showing a pre-'78 printed circuit? I've had mine apart enough to know what's what, but your Mitchell diagram is a handy reference.
Rich, do you have a diagram showing a pre-'78 printed circuit? I've had mine (1977 F250) apart enough to know what's what, but your Mitchell diagram is a handy reference.
Update, I have the dash lights fixed and still have some hair left on my head. What I ended up doing is bending up to a 45 degree angle the + and - tabs on the lamp holders so when I installed them the contacts had far better pressure and contact to the copper tracks. All lights are working but leaving the dash apart till I resolve the blower motor operation which is goofy at best. Will not run unless I hold the relay contacts closed then all 4 speeds run peachy. Maybe the relay is shot but have no idea how to bench test it, so may replace it and see what happens. What is weird it has power coming to the relay when the key is off or on. I thought relays got excited with current flow and then closed completing the circuit. Since this has flow at all times and never closes leads me to believe it is shot. So if my theory is correct and the new one excites and closes the contacts then they will stay closed and create a parasitic draw. Yeah I am baffled how this will go. I just find it strange that relay has power to it with the key off. Hope someone can tell me it should not be powered with the key off.
11-23-2017, 12:09 AM
