I just brought home a 38k original mile 70 Coronet 440 with a 383. Everything checks out ok BUT....when you turn on the parking lights the left inst. cluster turn signal light glows dim and the fuel gauge pegs. Turn on the left signal and same thing happens but the signal functions. Hit the brakes again same thing. Right signal no effect.

I have not had much time with it so far I pulled the forward harness at the bulkhead and checked connections and they are ok. Checked both front and rear left side bulbs and sockets..ok.

I will start the trouble shooting this weekend. I figured before I did I would throw it out there. Maybe someone here has had a similar odd ball issue and could save me some time.

The fact the T/S & brake light both effect it kinda eliminates the forward harness IMO, sounds like a bad ground on the left taillight, it feeds back throught the dash light circut which causes that bulb to glow then a marginal dash ground (probably the ground lead going to the steering column) so some of the current feeds through the fuel gauge pegging it...

Check the grounds, everywhere. Does the car have the right negative battery cable? It needs to be grounded to the body with the smaller wire, or have a ground strap from the block to the body, the steering column needs that ground wire to the mounting stud under the dash, the turn signal lights and taillight housings need to be bolted down securely to ground them. The insturment cluster needs to be screwed to the dash fram to ground it.

Thanks...I was leaning towards a ground problem. I will check it out this weekend and post up what I find.

I had really weird light problems on our 70 RR when we first got it. I had made a new rear wire harness to replace the hacked up one. I finally had everything hooked up and it had been working perfectly a couple of days before. I brought Michelle down to show her the now finally working lights and I had very similar problems. With advice from on here I realized it was a ground problems, as has been suggested for you (and I agree). I ran a ground wire from each taillight housing to the trunk latch support and at least THAT part of the electrical system has worked fine ever since. Yes, I know it is red not black wire but that is what I had. Good quality tinned marine wire with heat shrink ring connectors.

Your LF or LR running lamp bulb has a bad ground. The current flow is looking for ground. The current flows through the stop lamp filiment back to the dash cluster through the turn signal indicator bulb. It is finding ground at the dash cluster. Check your running lamp bulbs,sockets, and socket grounds. It could be any one of the three.
Doug

Well here is the deal as best I can figure it out. The rf filter attached to the voltage regulator on the back of the panel came loose from the screw that holds it to the panel. It made contact with the positive stud to the ammeter. At the same time it was touching the circuit board. A part of the board is showing damage. Mainly the upper left corner. It seems the fuel gauge goes haywire only when the instrument lamps are on or the left turn signal. If I remove the dash bulb for the turn signal the fuel gauge is fine.

Anyone know where I could find a schematic to the circuit board on a non rallye dash car?

I disagree on the bad cluster ground. Only 2 items are working improperly. A bad cluster ground would affect many cluster items. It is posible that there is a breach in the circut board (I just repaired this exact problem in a 64 Fury). But I still think the running light circut is seeking ground in the cluster. Perhaps thru the fuel gauge sender circut as well. I don't have a diagram in front of me right now, but if the cicut bard looks ok I would go with my original diagnosis. A bad ground is by far the most likly culpret.
Doug
Dou8g

I would still double-check the cluster grounds. Some clusters have multiple grounds, as some clusters have two circuit boards (left side, right side).

So if the Ammeter and Oil light work, but the fuel, temp and turn signals do not, I suggest checking that side. It never hurts to have more grounds than necessary.

Also, if things work fine when the lights are off, and things go screwy when lights are on, that is also an indication of a poor ground. Basically, you're overloading whatever ground circuit is still functioning, due to resistance, corrosion, etc.

I still say, check grounds on the cluster. Add one or two new ones just in case. All the clusters in all my cars work.

Well I checked thru everything and the circuit board is damaged no question. One area has lifted from the board and was burned. When you push on it or move the bulb at that area the fuel gauge goes crazy the left signal lights up or the high beam indicator lights. Or all or some. The temp gauge looks like it was damaged long ago as I have continuity to the gauge but it does not move even when I put voltage to it. I am guessing the circuit board is a lot worse off than what I can see.

I got an NOS temp gauge and figured I might as well get a new circuit board and tear it apart and fix everything at once. Anyone know of a vendor on here that sells the boards for the standard 120 mph panel?

You are looking at used for the board as far as I know .