First Truck Electrical Issues Help!

[Oliver.G]

Hello, I am 17 years old and bought a 1969 GMC long bed, two wheel drive about two months ago. Her 350 runs well. Lately as it has started raining more and more in my city the truck has been having electrical issues. The turn signals work sometimes and then stop completely until i jiggle the fuse boxand then they work again. However the hazards work always. Also, the front left headlight (quad headlight truck) is the only one that works on low beam of the four and then on high beam the other three light up but then left one stays on low beam. This is ofcourse very frustrating as it forces me to drive the truck during the day only at the moment. I have read that this may be an issue with the headlight dimmer on the floor. Please advise me how to diagnose and fix this problem. I want to fix her myself.

Some other info on the truck: 4 speed manual, 8 lug hubs, 3/4 ton springs in the bed, updated radio, auxilary flood lights on rear bumper, trailer brake kit, 2 extra fuel tanks under the bed


I am new to this forum so if this is the wrong place to post please direct me elsewhere. Thank you very much to all who read this and offer their opinion.

[70LonghornCST]

I moved this to "Electrical" for you. Hoping some of our resident experts will chime in for you.

[Oliver.G]

Thank you

[_Ogre]

turn signals work sometimes and then stop completely until i jiggle the fuse boxand then they work again. However the hazards work always

wiggling the fuse box is never a good idea, it could break wires or connections
if your hazards work your wiring is good, i suspect the turn signal flasher is loose or poor connections
pull both flashers the connections should look alike, if not take a pic and post it up

the front left headlight (quad headlight truck) is the only one that works on low beam of the four and then on high beam the other three light up but then left one stays on low beam

it sounds like you lost the ground on one headlight or the bulb is disconnected
what have you tried to get it working?

[Tron Man]

Oliver, glad to see you want to resolve your electrical problems yourself. Your turn signal problem sounds like a loose or defective flasher. Make sure that the flasher is seated. If your turn signal problem persists, replace the flasher. Note that your turn signal flasher is a different design than your hazard flasher. For your '69 GMC you will need a two bulb turn signal flasher like a Turn-Sol brand. A hazard flasher will work but you loose the burnt out bulb indication feature a turn signal flasher has.

For the headlight problem, check the grounds on each of the outer head lamp connectors. You should see a black wire from the head lamp connector that terminates to a ground on the radiator support structure. Undo each ground and check for corrosion. If there is corrosion use a small wire brush to clean the connections. Note that on GM products your inner bulbs light on bright only. If the grounds are OK you'll need to make voltage measurement on the outer head lamp connectors. Post back and let me know how you made out on the turn signal an head lamp ground issues. Also, do you have a multi-meter or 12 volt test lamp.

Tron Man,
Reno,NV

[Oliver.G]

I have already checked one of the grounds and it seemed to be in fair shape. However I will wire brush both of the grounds to be on the safe side. If the inner bulbs only light on bright is it possible that the right side headlight (which only works on bright) is just a burnt out low beam filament?

With regard to the flashers, it is most definitely a problem with seating as the flasher is very loosely connected to the fuse box and when they stop working it is due to it being out of place. Would a new flasher solve this problem? Or would you recommend I tape the flasher in place somehow to secure it better?

I do not own a volt meter, but I do have access to one.

Thank you very much for the quick and detailed reply to both of you (Tron Man and Ogre).

Oliver

[_Ogre]

both flashers are the same, try to swap the haz for the turn flasher
not owning a multimeter is no excuse; harbor fright gives them away and sears has them for $10
i see you a canuck, how boat going to canadian tire and see what they have for cheap?

cheap and free multimeters work fine for checking continuity and voltage
i owned a fluke for many years until i let the smoke out of it
now all i use is the freebies from harbor fright, i have 3 of them

[Tron Man]

Oliver, let's address the head lamp problem first. Since your grounds look OK remove the RH head lamp and examine the connector for corrosion. If the connector is clean the lamp is most likely has a open low beam filament. To make sure the lamp is defective you can check for voltage at the connector. Your head lamp low/high beam connector has three wires. Black=ground, Tan=low beam and Light Green=high beam. With the head lamp switch on and the dimmer switch on low beam, measure the voltage at the Tan wire connection to ground. If you measure 12 volts, then replace the head lamp. If you don't see 12 volts, then you'll have to find out why.

If your turn signal flasher is loose on the fuse panel, the female spade connectors located in the fuse panel may be spread out (loose) or broken. With the ignition switch off, probe each spade connector carefully and gently with a blade tip jeweler's screw driver and see if you can slightly bend each side of the female spade connectors toward the center. Again be very careful here. If this process doesn't work you may have to shim one or both flasher spade terminals with thin metal strips to tighten the connection.

As far as flashers go, there is a difference between turn signal flashers and hazard flashers. Turn signal flashers are wired in series within the flasher can and hazard flashers are wired in parallel in the flasher can. Again the reason for the difference is the series wired turn signal flasher will only flash if the front and rear turn signal bulbs are working. If one of the turn signal bulbs is burnt out, there is not enough current drawn through the flasher's heater element to activate the bi-metallic strip inside the flasher can. In this condition the driver will see a constantly lighted turn indicator on the dash indicating the a front or rear bulb is not working. A hazard flasher will work with burnt out bulbs or not due to the parallel wiring arrangement within the hazard flasher can. In summary a hazard flasher will work for turn signals, but the burnt out bulb indicator feature won't be available.

Let me know how you make out with the head lamps and turn signals. We'll keep pushing on these issues if need be.

Tron Man,
Reno Nevada

[Oliver.G]

The problematic flasher that was in use was a hazard flasher as it never gave me the burnt out indication. I swapped the two flashers and the problem seems to be fixed now.

I will check with a voltmeter the wires at the light housing and then replace the light if that is the problem.

I will update you as I do this.

I cannot thank you guys enough for the help. This is a newbie problem and seems very simple, but as I am new to all this your advice is very apreciated.

[Oliver.G]

I replaced the headlight and all is good now. Thank you for your help. I realize that it wasnt even a problem and only the light needed replacement. However my knowledge of multimeters and such has improved and I have you guys to thank.