Electrical current flowing to the headlamp bulb, and resistance to that flow of electrical current are the Number 1 and Number 2 creators of heat in that area. Nothing else even comes close. 

► The first question is: What is the Wattage of your head lamp bulb ? In years gone by, it was a popular "upgrade" to install bulbs of up to 100W. The OEM 65W bulb draws about ~4.6A, the 100W about ~7.2A... almost double. 

► The second question is: Did you coat the terminals of the present HL bulb with an anti-oxidation compound ? Corrosion on the HL connector will be the most probable source of resistance which causes the heat. Corrosion on electrical connectors can only be controlled long-term by anti-oxidation compounds. This corrosion is ALREADY present on your 40 year-old motorcycle. 

I highly suggest you use the SEARCH function on this board to find posts related to selection of an LED HL bulb to replace your H4 incandescent bulb. We cannot recommend an exact bulb PN because the development of LED bulbs is changing too fast. But basically you are searching for:
• H4 dual beam replacement bulb
• 3000L (lumens) or higher
• 5000K (color of the light) or higher  [5000K is white, 6000K is that piercing blue-white]
• If you have zero "user experience" with LED headlamp bulbs, then the slightly more expensive 3-sided central column seems to give a fuller, better light pattern for motorcycles, than the cheaper 2-sided construction intended for cars. 

Using an LED bulb will typically reduce your current draw to less than 25W (1.7A) while the light output is about double. This reduces the stress on the rectifier board, adds charging capability to your battery, AND increases your on-the-road visibility/safety with on-coming drivers.

When adding the LED bulb, we also suggest that you remove the 3-prong sub-reflector inside the main headlamp reflector. Additionally, for increased riding safety consider riding with the Hi-beam ON during the day.

Hope this helps.

@wobbly Richard, many thanks. I do have the recommended OEM bulb but have yet to try LEDs. Now's the time. I am in the process of checking all my contacts and yes- finding corrosion so time to add anti ox compound throughout. 

Thanks for your time and advise.

✦ I just looked on Amazon and they have a $19 LED bulb that looks like it will do the job. CLICK HERE. You might find something with a higher Lumen output, but at least the pictures and specs describe a bulb with the correct physical construction and pretty good illumination stats. Five years ago I paid $55 for a bulb like this.

✦ When these bikes were new in the 1970's and 80's, riders like my parents repeatedly criss-crossed the country by the thousands in all sorts of weather on Airheads. All those day-long rain storms allowed water into the connectors, which years later has led to the corrosion you now see. If not the rain, then 40 years of bike washing. So it's not just the touring RT's that need help, I estimate that well over 90% of the Airheads still on the road have this issue in some form or another. 

When you hear your horn get louder or see your turn signals operating better after the treatments... then you start to wonder what improved in your charging system and ignition system that you can't hear or see.

Hope this helps.

Well I'm still at it. Learned to check relays this weekend- the headlight and starter relays test out fine. I'm cleaning all my connections and adding anti-ox compound. I've checked the starter motor (visually only) and see no corrosion at all- looks great. I have run into another stumper. My new headlight socket and wire arrived with a black, gray, and yellow wire.  There is a red wire from the original headlight socket that goes to a switch (?) inside the upper right part of headlight with a toggle on the outside of the headlight. I'm operating from a Haynes workshop manual and see no indication of this switch on the electrical schematic? The starter is still operating intermittently. 

That switch is obviously an owner-added option. From the sound of it, it's most likely to turn OFF the headlamp during the day. Besides being totally unsafe in the era of car operators too busy texting to "drive", in this day of low-current LED lighting is also totally unnecessary.

The 3 wires from your headlamp plug should all plug directly into the multi-color circuit board. The OEM color pattern is White (hi-beam), Yellow (low-beam), and Brown (DC return). This may not be the colors on your new HL socket, but the functions are still there. Look very closely at the hard plastic part of the socket and some of them have tiny text telling the function of each wire position. That may help you.

On the stock wiring system there is NO headlamp relay. That was also a probable owner add-on to add reliability when using the 100W HL bulbs that were all the rage in the 1980's. As previously discussed, these days the common LED replacement bulb can easily surpass that lumen output using 1/4 the current. Using an LED bulb moves the presence of a HL relay and all its extra wiring into the negative reliability column. If this was my bike, in keeping with the KISS principle, the wiring would be simplified and returned to its original factory condition.

Hope this helps.

I eliminated the above mentioned switch and have a nice bright stock bulb. Out of curiosity I checked my '81 RT and found a similar switch which I will also remove when I'm in that headlight next.

I will order and try the LED option- very much looking forward to the difference. 

Unfortunately I still have an intermittent starter button. I've checked all connections, and thought I may have a problem with the starter button itself which I have to press numerous times before the motor (starter) engages. I lightly scratched up the spring loaded connection in the button which worked last night, but today I'm back with nothing. 

Might this be a starter solenoid issue? 

Thank you!!!!

Posted by: @8477

Unfortunately I still have an intermittent starter button. I've checked all connections, and thought I may have a problem with the starter button itself which I have to press numerous times before the motor (starter) engages. I lightly scratched up the spring loaded connection in the button which worked last night, but today I'm back with nothing. 

Might this be a starter solenoid issue? 

A) The starter circuit is special in that it contains not one, but two relays... and both should be checked. But there is a sequence to the testing....

✦ Step 1: The button on the handlebar controls the "Starter Relay". This is a small cubical relay package on the LH side of the frame, under the fuel tank, opposite the voltage regulator. If you don't know how old this relay is, then REPLACE IT !! Treat the male contacts on the new relay with anti-oxidation compound (like No-Ox-Id) BEFORE plugging it into the relay socket. This usually fixes about 80% of all "starter button issues". (And believe me when I say that treating the new relay contacts is VERY important.)

✦ Step 2: In turn, the Starter Relay energizes the Starter Solenoid. This is nothing but a high current relay, and this relay closes the contacts that actually energize the starter motor proper. After the Starter Motor Cover is removed, you can test the solenoid in place by touching a wire from the Battery + Terminal directly to the small 1/4" terminal (the smallest contact) on the solenoid. This test bypasses the Ignition Switch, Handlebar Button, the Starter Relay and all the interconnection wiring. 

B) The use of the electric starter also depends upon the reliability of 2 other small switches which are also prone to failure....

✦ The Gear Box Neutral Switch acts as a safety so that the bike is not started "in gear". If your green Neutral Lamp is working OK, then this switch is probably OK. 

✦ The Clutch Lever Switch is very prone to failure since it is actuated with every single gear shift. It is a simple ON/OFF switch you can test in-situ after disconnecting the 2 leads inside the headlamp shell from the multi-color circuit board. Simply take the 2 disconnected leads and connect them to your Ohm Meter. You should see definitive "make/break" readings as the lever is pulled in and released.

As reliability goes... Items 1, 3 and 4 are much more likely to fail than the Starter Solenoid, which is not only far more robust, but also much better protected from the weather and wash water.

Hope this helps.

PS. While the Starter Motor Cover is removed for inspection is an excellent time to check the condition of the high current battery cable coming from the Battery + Terminal. On the OEM battery cable, battery acid is known to wick under the jacket, all the way from the battery to the solenoid !! This destroys the connection at both ends of the cable. And that cable not only carries all the current for engine starting, but also 100% of the battery charging current from the alternator and rectifier. So the condition of the cable AND its 2 terminals can't be overstated. If you see ANY green coloration or white corrosion on that cable at the Starter Motor end, then the cable MUST be replaced.

OEM battery cable showing presence of wicked battery acid

Posted by: @wobbly

On the stock wiring system there is NO headlamp relay. That was also a probable owner add-on to add reliability when using the 100W HL bulbs that were all the rage in the 1980's. 

I don't want to mislead you or make things worse. There IS a headlamp relay on the stock wiring system. This relay turns the headlamp OFF during use of the electric starter. This is necessary because, as previously stated, the headlamp bulb is a very large user of electrical power, second only to the starter itself.

The headlamp socket plugs into the multi-color circuit board. Then wires from that board jump over to a rectangular relay located at the 5 o'clock position as you face rearward, looking into the headlamp shell. 

Just want to make sure that relay stays in place.

I may have located the issue- replaced the starter relay with a new one. The starter solenoid works fine. All connections are clean (freshly lubed now) and tight. The gear box neutral light has been out since early summer but starting the bike easily with the clutch pulled in- will replace it today. 

However pulled the two brown yellow wires from terminal 85B and ohm tested- no on/off reading. I have further discovered that if I press the ignition button and pull clutch in and out I get intermittent starter engagement. 

I'm totally befuddled as to where this on/off switch is? 

I'll replace the gear box neutral switch next. 

Leaning lots! Thanks!!

Posted by: @8477

I have further discovered that if I press the ignition button and pull clutch in and out I get intermittent starter engagement. 

I think you mean "the starter button". 

Please test the clutch lever switch for consistent operation. If there is any doubt, then replace it. It's probably done several million make/break connections during its long life. 

I'll replace the gear box neutral switch next. 

Neutral light not working could be the g/b switch, the bulb, or the interconnecting wiring.  Srart with some testing.

Leaning lots! Thanks!!

I had the same problem. Then I cut back on the beer while working on the bikes. 🤣