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RE: Dash Lights and Turn Signals

To: <>
Subject: RE: Dash Lights and Turn Signals
From: "James Fischer" <>
Date: Sat, 30 Sep 2006 23:41:37 -0400
> My dash lights are not functional. I have power to the
> dash light reostat, so I suspect the reostat itself as the culprit.
> Can it be bypassed by simply connecting the 3 red wires attached to it
> to the red-white dash light wires?

Dad and I just completed the installation of a new wiring harness
into an 1952 MG-TD (a multi-day process), so this subject is very
fresh in my mind.  I am not sure that '53s are wired exactly the
same as the '52s, but I will assume they are.

Yes, you can simply move the red/white wire from one of the posts
on the driveshaft tunnel side to the unused post directly under
(or over) where the solid red wire connects.  Then your lights
are "full on" at all times when switched on.

But you have THREE red wires to the rheostat?  That's unusual.
There is only one going there on a '52.  We have three red wires
to the ignition switch, and only one red wire (part of the tiny
wiring harness that handles all the "details" on the dashboard)
to the dash light rheostat.  Maybe someone re-wired your dash.
Maybe 53's are different.

The dash lights are all daisy-chained on the red/white wire and the
ground for the bulbs is obtained through the rusty tube into which
one inserts the rusty tab, which connects to the bulb.  Gauges are
grounded with black wires, while the lights on the dash itself are
grounded through the metal plate to which they are attached.

Before blaming an innocent rheostat that never carried much current
at all, try looking for voltage on the output side of the rheostat
(the pair of lugs towards the drive shaft tunnel where your red/white
wire connects now.  Or just pull out a bulb socket, and check the
voltage at a bulb, connecting the ground lead on your meter
to a "known good ground", such as the handbrake lever, or a
bolt on the firewall.

If you have voltage at either the rheostat or a bulb (and you
may have to twiddle the knob a bit to get one) then the rheostat
is fine, and your problem can be either a mass bulb death
(possible, but improbable) or bad grounds (more likely).

> Also, my turn signals have never functioned. I installed a new flasher
> unit. The turn signal switch must be held in the left or right position.
> Is it supposed to hold itself for a few seconds or must it be held
> manually?

Ours is the same way.  One must hold it over to one side or the
other, but if one does, the turn signals work just fine.
Anyone got one that stays put for a while before turning itself

> How prone to failure is the turn signal relay box? Any
> suggestions for tracing the problem.

Oh wow, in an MG-TD, the turn signal wires are at least half of
the wires in the car!

I'd suspect the flasher, the common power connection to it, or the
"feed" connection to the switch, rather than the relay box, as the
relay box is very over-engineered, and could handle the current from
much larger loads with ease.

If jumpering across the flasher terminals do not make
the appropriate sidelights go "on" when the turn signal lever
is pushed to one side, get out the shop manual and re-draw the diagram,
starting at the fuse where the wire from the 3-terminal flasher connects.
Just "trust" the relay box, and check all the wires with a longer
wire attached to one of the probes on your ohm meter (pulling the fuse
or pulling a battery cable is a good idea before your start trying
to check connections with the ohm meter.

If all checks out, then you may have a bad relay box.


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