Dash lights dim, only 9.6 volts at light sockets.

7173Mustangs.com

Help Support 7173Mustangs.com:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

dogbiscuit

Well-known member
Joined
May 23, 2022
Messages
53
Reaction score
3
Location
Ogden, UT
My Car
1971 Mach1 429SCJ Ram Air Drag Pak
My dash lights remain dim/underpowered when the light switch rheostat is fully turned up. Any ideas?
 
Make sure you have a good chassis ground. The original negative battery cable grounded to the right inner fender panel and the engine block.
You can try pulling the headlight switch and cleaning the rheostat coil and contact.
You may want to try a separate relay setup for your headlights. @TheRktmn makes them, and they are available from other sources.
 
The single best thing you can do is add a relay. Right now all the headlight power goes through he switch. By adding a relay the headlights are powered by the relay and the dash lights by the headlight switch. It takes a tremendous amount of work (amperage) off of the old wiring. The dash lights will brighten up and the headlights will see alt voltage 13.5
 
While you're at it change the bulbs (except the ALT bulb if idiot lights) to HiPoParts.com Elite Series II LED's. That alone will make a huge difference. I recommend HiPoParts as all LED's are NOT created equal.
Relays for the headlights will also make a huge improvement regardless of type used.
There has been lots posted on this subject.
 
If you do install LED lights to replace the old incandescent bulbs, be aware the LED lights are polarity sensitive. If an LED is not working turn it 180 degrees and try again.
 
While you're at it change the bulbs (except the ALT bulb if idiot lights) to HiPoParts.com Elite Series II LED's. That alone will make a huge difference. I recommend HiPoParts as all LED's are NOT created equal.
Relays for the headlights will also make a huge improvement regardless of type used.
There has been lots posted on this subject.
I purchased ny light relays from RocketMan at:

https://www.rccinnovations.com/index.php?show=menu-hrk-all

Easy installation, no wires to cut or splice. High quality product. Be sure to order the correct on for you year model.
 
The single best thing you can do is add a relay. Right now all the headlight power goes through he switch. By adding a relay the headlights are powered by the relay and the dash lights by the headlight switch. It takes a tremendous amount of work (amperage) off of the old wiring. The dash lights will brighten up and the headlights will see alt voltage 13.5
Do you happen to have a wiring diagram for this, or even a simple drawing?
 
Do you happen to have a wiring diagram for this, or even a simple drawing?
If I recall correctly, Rocketman has a drawing of how the relay is installed. I found this drawing online at:

https://www.rccinnovations.com/Instructions/RelayPac-Single.pdf


There are other similar drawings for various kits and applications. To see all of the instructions for his various solutions see:

https://www.rccinnovations.com/index.php?show=wiring


Realistically, the drawing may make the installation look more difficult than it actually is, but it is definitely a useful drawing. The mini-relay kit was very easy to install. And, no vehicle wires need to be cut. It is the kind of enhancement any Ford enthusiast ought to get and install on their vintage vehicle.

The full-relay kit is a little more complex as it uses two relays, one for each side. In my opinion the full-relay kit is overkill for most folks, But for someone with really high amperage demand due to their selection of illumination products, the full-relay kit provides for much higher amperage draw for the relevant lighting. YMMV...

In short, whether you purchase the mini-relay or full-relay kit, you really can't go wrong. The result is a system modified in a manner Ford should have used to begin with, IMHO...
 

Latest posts

Back
Top