Lights dim

[Mrturner1]

Well I have been driving my truck EVERYWHERE lately because this puppy is finally road worthy and safe (relatively of course) and I've been noticing that when I come to a stop light and it idles down, when I take off the lights get a little bit brighter. Also, when I hit the manual electric fan switch, the gauges all get a shade or two dimmer. It's not an emergency but after all the time and money I've put in I want it tip top ya know? It's got a bran new Powermaster 105A alternator, and all I have for amperage draw is my dual electric fans, the MSD Pro Billet HEI, the factory gauge cluster with 3 Autometer 2 1/16" ultra light gauges, and a 6" Autometer tachometer. When I installed the new alternator a few weeks back, I used good heavy gauge wire, good connections, and everything is wired correctly now that I've scoured through the nightmare that was my wiring.

[bow-tie-bandit]

Talk to Mark at Mad electric. http://www.madelectrical.com He can help you out. Phone number is on his web page and be prepared to be on the phone for awhile. Tell him what your electrical gremlins are and he can give you the answers. He is out of California also.

[firedemon]

did you use relays for your fans and headlights?

[leftybass209]

Are you still running a stock harness that you've cleaned up, or are you running an aftermarket harness?

Even some of the newest vehicles have the small lighting issues you're describing. Electric fans draw a lot of current, and high current alternators demand a lot from an engine; so much so that many vehicles have a noticeable temporary drop in RPMS just because the alternator kicked on. Much of it comes down to engineering, and it's not easily diagnosed in a forum by saying, upgrade this wire to 12ga, this wire to 8ga, and you're good to go.

Ideally, you'll want to over ground the vehicle. I typically go overboard, and do both sides of a vehicle. Whatever I do to the right, I do to the left. 2 core supports, 2 engine to frame, 2 engine to firewall, 2 body to frame, 2 bed to frame. Then I'll look at the battery to alternator connections.

Do you have a headlight relay system? It pulls current directly from the battery, instead of routing it through the headlight switch. This helps maintain a more consistent power source to your lighting, and extends the longevity of your light switch by removing the high current running through it as wired stock.

I could also recommend you setting up LED lighting in those gauges. They require hardly any voltage or current, and provide a brighter more consistent backlight.

I hope that helps. Best of luck!

[Mrturner1]

Originally Posted by firedemon

did you use relays for your fans and headlights?

I have the relay that came from Flexalite wired up for the fans, but the headlights are still wired up stock

[Mrturner1]

Originally Posted by leftybass209

Are you still running a stock harness that you've cleaned up, or are you running an aftermarket harness?

Even some of the newest vehicles have the small lighting issues you're describing. Electric fans draw a lot of current, and high current alternators demand a lot from an engine; so much so that many vehicles have a noticeable temporary drop in RPMS just because the alternator kicked on. Much of it comes down to engineering, and it's not easily diagnosed in a forum by saying, upgrade this wire to 12ga, this wire to 8ga, and you're good to go.

Ideally, you'll want to over ground the vehicle. I typically go overboard, and do both sides of a vehicle. Whatever I do to the right, I do to the left. 2 core supports, 2 engine to frame, 2 engine to firewall, 2 body to frame, 2 bed to frame. Then I'll look at the battery to alternator connections.

Do you have a headlight relay system? It pulls current directly from the battery, instead of routing it through the headlight switch. This helps maintain a more consistent power source to your lighting, and extends the longevity of your light switch by removing the high current running through it as wired stock.

I could also recommend you setting up LED lighting in those gauges. They require hardly any voltage or current, and provide a brighter more consistent backlight.

I hope that helps. Best of luck!

I wondered about the stock harness. I haven't upgraded to an aftermarket wire harness yet but I've been thinking about going that route lately. Do aftermarket harnesses have oversized wire?

[firedemon]

its worth doing headlights even with a new harness

[Andy4639]

Head lights electric fans AC wipers electric windows any electric that really put a amp draw on the system should have relays installed. That being said doesn't matter if new are old wiring harness is installed either.

Check the belt tension also first thing. The belt could be a little loose. Connections on lights could need cleaning up also.

[midniteblues]

You replaced the alt with a higher output one.but are you still running the oe or replacement mech. Voltage regulator?

Just asking cause they are set too only let so much juice through the system. So your higher output alt really isnt doing anything more.

I've had the same symptoms your describing with a bad alt.

I notice in my car when the elec. Fans kick on the electric system takes a big hit and just for a split second i'll kinda get a blink but it recovers almost instantly and the lights go rite back too full power.....but this alt is internally regulated.

Do the easy stuff first check and clean all the grounds.
there is one on each side of the back of your headlites i would start there.

Yes on relays they make a world of differance.
also your headlite switch could be getting worn out. Ive seen them get hot allready so i would check that out also.

[Andy4639]

The reason for relays.

#1 reason it takes the load off the system no matter if you have a 30 year old system are brand new wiring system.

System load:

Power comes from battery to alternator to horn relay feeder on fire wall to headlight switch them down to dimmer switch then to headlights. All of the amp load is on the whole system. (basic wiring)

When relays are used:
The amp draw is straight from battery are alternator to relay to head lights.

This will insure your head light and dimmer switches will last a lot longer than before.