[Healeys] Ballast resistor wiring question

Bob Spidell bspidell at comcast.net
Thu Dec 26 10:12:55 MST 2019

The Moss catalog states 'You will need one [resistor] for each side of 
the car,' so I don't think it matters where you put them, as long as 
they are in parallel in the circuit.  50W resistors are pretty large, so 
I wouldn't want them in the engine bay; in the boot near the lights 
would be my preference.

Resistor ratings are typically given in the load the resistor can 
withstand without letting the smoke out, not how much power it will 
pull--since voltage of the circuit the resistor is to be installed in 
often isn't known--but Moss isn't specific about this.  The turn signal 
circuits are separate--although Moss implies they can somehow bleed 
through--so the power draw isn't additive*.  The Moss catalog mentions 
the 'application data in the schematic section of this catalog' but I'll 
be damned if I can find said section and the search function on the 
website yields no useful results; anybody know the page# in the current 

The catalog is confusing as it states you'll need an electronic flasher 
if you install LEDs, then gives the option to install load resistors; 
presumably, if you don't want to replace your old-school flasher.


* theoretically, since the flasher operates both sides of the signals 
you could put a single resistor on the 'signal' terminal of the flasher 
(IIRC, the flashers have GND, power and 'signal' terminals).

On 12/26/2019 7:05 AM, Michael Salter wrote:
> After due consideration I've come to realize that there is a problem 
> with the planed resistor installation.
> The original Lucas "thermal " type flasher unit is rated at 42 watts.
> The resistors that are shown on the Moss web site are 50 watt.
> If you were to install such a resistor, to simulate the load, on each 
> turn signal bulb the load through the flasher unit, when the signals 
> were selected, would be 100 watts PLUS whatever the LED lamps drew. 
> This would result in 8.3 amps flowing through the flasher unit  ... 
> probably enough to burn it out!!
> I would think that a far better solution would be to install two 50 
> watt resistors.
> On the turn signal relay (that mysterious metal box mounted on the 
> left front inner fender). One 50 watt resistor would be installed 
> between terminal 2 and ground and the other between terminal 6 and ground.
> Those original flasher units are becoming VERY hard to find so it 
> would be a pity to cook any more of them.
> M
> On Tue, Dec 24, 2019, 10:30 AM Michael Oritt, <michael.oritt at gmail.com 
> <mailto:michael.oritt at gmail.com>> wrote:
>     Thanks all.  What Kees says flies in the face of both Moss's
>     (slightly inarticulate) instructions as well as the consensus of
>     the group.  I will install ONE resistor in the flasher lead of
>     each lamp, two--not four--resistors total.
>     Best--Michael Oritt
>     On Tue, Dec 24, 2019 at 10:22 AM Bob Haskell
>     <rchaskell at earthlink.net <mailto:rchaskell at earthlink.net>> wrote:
>         Per the Moss video, you're creating a new ground path to
>         prevent all
>         lights blinking when you turn on the left or right turn
>         signal.  So
>         connect the ballast resistors to the turn signal circuit.
>         Cheers,
>         Bob Haskell
>         Austin Healey 3000 BN7/BT7 registrar
>         On 12/24/19 9:22 AM, Michael Oritt wrote:
>         > I purchased two of the Moss 170-941 red LED bulbs to use as
>         > tail-lights/brake-lights to replace the standard 1157 dual
>         filament
>         > bulbs on my 100 (I have the reflector pods electrified and
>         wired for
>         > turn signals).  In addition to the bulbs I also purchased,
>         at Moss's
>         > suggestion, two 170-965 Load Resistors.
>         >
>         > The instructions for installation of the resistors simply
>         talk about the
>         > resistor's being installed between the power and ground
>         leads to each
>         > fixture but it does not specify which power lead.  My
>         question is:  do I
>         > connect the ground lead to the tail light power lead or the
>         turn signal
>         > power lead or does it matter?  I cannot envision connecting
>         it to both
>         > as that would defeat their separate function.
>         >
>         > TIA....Michael Oritt
>         > 

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